Search

In the spring and summer, high rates of primary production occur in the California Current Ecosystem (CCE) when nutrients are supplied to the euphotic zone. During periods of intense coastal upwelling, a flux of the micronutrient iron comes from nearshore sedimentary sources. In this upwelling region, mesoscale filament features distribute iron laterally, leading to distinct iron‐influenced ecological zones. This study is the first to focus on the biogeochemical links between iron, the macronutrients, and particulates in coastal upwelling filaments. Broad spatial patterns of iron and biogenic silica concentrations, and proxies of iron‐stress of diatoms, support results from microcosm amendment studies conducted during CCE Long Term Ecological Research process cruises in the summers of 2017 and 2019. We found that the benthic boundary layer and shoreward filament endmember supply dissolved and total dissolvable iron to this feature, but rapid assimilation and sinking by biogenic particles (e.g., diatoms) depletes the surface concentrations. Subsequently, diatom blooms which form in recently upwelled water masses become iron limited over time, thereby affecting the ratios of surface macronutrient reservoirs and biogeochemical advective fluxes. The development of Fe‐limitation during lateral advection may lead to efficient carbon export downstream and offshore of the region with the highest phytoplankton growth rates and productivity. Plain Language Summary: Along the western continental margin of the United States, seasonal upwelling filaments appear as fast‐flowing waters with high concentrations of nutrients (e.g., nitrate, silicic acid, iron) and phytoplankton. Diatoms dominate the phytoplankton communities in filaments, and they accumulate particulate matter as organic carbon and dense biogenic silica. During transport offshore, diatoms quickly deplete the surface of the critical micronutrient iron (Fe) and become Fe‐limited. Using shipboard incubation experiments, we show that Fe‐stressed diatom communities become more heavily silicified, and thus denser. Iron‐stress indicators consistently correspond with these phytoplankton community biochemical reconfigurations in two separate studies of filaments, thereby demonstrating a mechanism for enhanced diatom community export out of the surface ocean in later stages of filaments. Key Points: Upwelling filaments become Fe‐limited features in the ocean, as sinking diatoms deplete surface dFe concentrations and are advected offshoreIron‐limitation of diatom blooms is evidenced by in situ geochemical proxies (e.g., negative Siex) and deckboard Fe amendment experimentsGreater biogenic silica‐to‐particulate organic carbon ratios among diatom communities make filaments hotspots of particulate matter export [ABSTRACT FROM AUTHOR]

Changing temperatures will impact food webs in ways we yet to fully understand. The thermal sensitivities of various physiological and ecological processes differ across organisms and study systems, hindering the generation of accurate predictions. One step towards improving this picture is to acquire a mechanistic understanding of how temperature change impacts trophic interactions before we can scale these insights up to food webs and ecosystems. Here, we implement a mechanistic approach centered on the thermal sensitivity of energetic balances in pairwise consumer–resource interactions, measuring the thermal dependence of energetic gain and loss for two resource and one consumer freshwater species. Quantifying the balance between energy gain and loss, we determined the temperature ranges where the balance decreased for each species in isolation (intraspecific thermal mismatch) and where a mismatch in the balance between consumer and resource species emerged (interspecific thermal mismatch). The latter reveals the temperatures for which consumer and resource energetic balances respond either differently or in the same way, which in turn informs us of the strength of top‐down control. We found that warming improved the energetic balance for both resources, but reduces it for the consumer, due to the stronger thermal sensitivity of respiration compared to ingestion. The interspecific thermal mismatch yielded different patterns between the two consumer–resource pairs. In one case, the consumer–resource energetic balance became weaker throughout the temperature gradient, and in the other case it produced a U‐shaped response. By also measuring interaction strength for these interaction pairs, we demonstrated the correspondence of interspecific thermal mismatches and interaction strength. Our approach accounts for the energetic traits of both consumer and resource species, which combined produce a good indication of the thermal sensitivity of interaction strength. Thus, this novel approach links thermal ecology with parameters typically explored in food‐web studies. [ABSTRACT FROM AUTHOR]

Calanoid copepods comprise around 90% of Arctic zooplankton biomass and are fundamental to the ecological and biogeochemical functioning of high-latitude pelagic ecosystems. They accumulate lipid reserves during the productive months and represent an energy-rich food source for higher trophic levels. Rapidly changing climate in the Arctic may alter the quantity and composition of the food environment for one of the key copepod species, Calanus finmarchicus, with as yet unquantified effects on its production. Here we present rates of feeding and egg production in female C. finmarchicus exposed to the range of feeding conditions encountered across the Fram Strait in May/June 2018. Carbon (C) budgets were constructed and used to examine the relationship between feeding and growth (= egg production) in these animals. C-specific ingestion rates (mean ± standard deviation) were highly variable, ranging from 0.015 ± 0.004 to 0.645 ± 0.017 day-1 (mean = 0.295 ± 0.223 day-1), and were positively correlated with food availability. C-specific egg production rates ranged from 0.00 to 0.049 day-1 (mean = 0.012 ± 0.011) and were not correlated with either food availability or ingestion rate. Calculated gross growth efficiencies (GGE: growth/ingestion) were low, 0.12 ± 0.13 (range = 0.01 to 0.39). The assembled C budgets indicate that the average fraction of ingested food that was surplus to the requirements for egg production, respiration and losses to faecal pellets was 0.17 ± 0.42. We suggest that this excess occurred, at least in part, because many of the incubated females were still undergoing the energetically (C-) expensive process of gonad maturation at the time of sampling, an assertion that is supported by the relatively high C:N (nitrogen) ratios of the incubated females, the typically low egg production rates, and gonad maturation status. Ontogenetic development may thus explain the large variability seen in the relationship between egg production and ingestion. The apparently excessive ingestion rates may additionally indicate that recently moulted females must acquire additional N via ingestion to complete the maturation process and begin spawning. Our results highlight the need for improved fundamental understanding of the physiology of high-latitude copepods and its response to environmental change.

Coevolution between predator and prey plays a central role in shaping the pelagic realm and may have significant implications for marine ecosystems and nutrient cycling dynamics. The siliceous diatom frustule is often assumed to have coevolved with the silica-lined teeth of copepods, but empirical evidence of how this relationship drives natural selection and evolution is still lacking. Here, we show that feeding on diatoms causes significant wear and tear on copepod teeth and that this leads to copepods becoming selective feeders. Teeth from copepods feeding on thick-shelled diatoms were more likely to be broken or cracked than those feeding on a dinoflagellate. When fed a large diatom, all analyzed teeth had visible wear. Our results underscore the importance of the predator-prey arms race as a driving force in planktonic evolution and diversity., Competing Interests: Competing interests statement:The authors declare no competing interest.

Environmental DNA metabarcoding (eDNA metaB) is fundamental for monitoring marine biodiversity and its spread in coastal ecosystems. We applied eDNA metaB to seawater samples to investigate the spatiotemporal variability of plankton and small pelagic fish, comparing sites with different environmental conditions across a coast-to-offshore gradient at river mouths along the Campania coast (Italy) over 2 years (2020-2021). We found a marked seasonality in the planktonic community at the regional scale, likely owing to the hydrodynamic connection among sampling sites, which was derived from numerical simulations. Nonetheless, spatial variability among plankton communities was detected during summer. Overall, slight changes in plankton and fish composition resulted in the potential reorganization of the pelagic food web at the local scale. This work supports the utility of eDNA metaB in combination with hydrodynamic modelling to study marine biodiversity in the water column of coastal systems. This article is part of the theme issue 'Connected interactions: enriching food web research by spatial and social interactions'.

Bioseston is a heterogeneous assemblage of bacterioplankton, phytoplankton, zooplankton, and planktonic debris. A detailed knowledge of biosestons is essential for understanding the dynamics of trophic flows in marine ecosystems. The distributional features of seston biomass in plankton (micro- and mesoplankton) in the Southwest Atlantic Ocean (Rio de Janeiro State, Brazil) were analyzed using stratified samples gathered to a depth of 2,400 m during night time. The horizontal pattern of biomass distribution was analyzed vis-a-vis station depth during both wet and dry periods, with higher values recorded in the continental shelf than in the slope, confirming the terrestrial contribution of nutrient sources to the marine environment. This horizontal variation reinforces the occurrence of seasonal vortices in Cabo Frio and Cabo de São Tomé on the central coast of Brazil. Environmental variables reflect the hydrological signatures of the water masses along the Brazilian coast. The largest seston biomass was related to high temperatures, salinities, and low inorganic nutrient concentrations in tropical and South Atlantic central waters. The observed distribution patterns suggest that seston biomass in plankton in the region may be structured based on partitioned horizontal and vertical habitats and food resources.

Aims: This research aimed to analyze cutting board surfaces in seafood markets to find Vibrio parahaemolyticus, assess the isolates' ability to form biofilms, generate and evaluate characteristics of plasma-activated water (PAW), and compare the effect of PAW on planktonic and biofilm cells of the isolated V. parahaemolyticus strains., Methods and Results: A total of 11 V. parahaemolyticus strains were isolated from 8.87% of the examined cutting boards. Biofilm-forming ability was evaluated for these isolates at temperatures of 10°C, 20°C, and 30°C using crystal violet staining. Four strains with the highest biofilm potential were selected for further analysis. The pH of the PAW used in the study was 3.41 ± 0.04, and the initial concentrations of hydrogen peroxide, nitrate, and nitrite were 108 ± 9.6, 742 ± 61, and 36.3 ± 2.9 µM, respectively. However, these concentrations decreased significantly within 3-4 days during storage at room temperature. PAW exhibited significant antimicrobial effects on V. parahaemolyticus planktonic cells, reducing viable bacteria up to 4.54 log CFU/ml within 20 min. PAW also reduced the number of biofilm cells on stainless steel (up to 3.55 log CFU/cm2) and high-density polyethylene (up to 3.06 log CFU/cm2) surfaces, although to a lesser extent than planktonic cells., Conclusions: PAW exhibited significant antibacterial activity against V. parahaemolyticus cells, although its antibacterial properties diminished over time. Furthermore, the antibacterial activity of PAW against biofilm cells of V. parahaemolyticus was less pronounced compared to the planktonic cells. Therefore, the actual effectiveness of PAW in seafood processing environments can be affected by biofilms that may form on various surfaces such as cutting boards if they are not cleaned properly., (© The Author(s) 2024. Published by Oxford University Press on behalf of Applied Microbiology International.)

In the Atlantic Arctic, bowhead whales ( Balaena mysticetus ) were nearly exterminated by European whalers between the seventeenth and nineteenth centuries. The collapse of the East Greenland-Svalbard-Barents Sea population, from an estimated 50 000 to a few hundred individuals, drastically reduced predation on mesozooplankton. Here, we tested the hypothesis that this event strongly favoured the demography of the little auk ( Alle alle ), a zooplanktivorous feeder competitor of bowhead whales and the most abundant seabird in the Arctic. To estimate the effect of bowhead whaling on little auk abundance, we modelled the trophic niche overlap between the two species using deterministic simulations of mesozooplankton spatial distribution. We estimated that bowhead whaling could have led to a 70% increase in northeast Atlantic Arctic little auk populations, from 2.8 to 4.8 million breeding pairs. While corresponding to a major population increase, this is far less than predicted by previous studies. Our study illustrates how a trophic shift can result from the near extirpation of a marine megafauna species, and the methodological framework we developed opens up new opportunities for marine trophic modelling.

Predator responses to warming can occur via phenotypic plasticity, evolutionary adaptation or a combination of both, changing their top-down effects on prey communities. However, we lack evidence of how warming-induced evolutionary changes in predators may influence natural food webs. Here, we ask whether wild fish subject to warming across multiple generations differ in their impacts on prey communities compared with their nearby conspecifics experiencing a natural thermal regime. We carried out a common garden mesocosm experiment with larval perch ( Perca fluviatilis ), originating from a heated or reference coastal environment, feeding on zooplankton communities under a gradient of experimental temperatures. Overall, in the presence of fish of heated origin, zooplankton abundance was higher and did not change with experimental warming, whereas in the presence of fish of unheated origin, it declined with experimental temperature. Responses in zooplankton taxonomic and size composition suggest that larvae of heated origin consume more large-sized taxa as the temperature increases. Our findings show that differences between fish populations, potentially representing adaptation to their long-term thermal environments, can affect the abundance, biomass, size and species composition of their prey communities. This suggests that rapid microevolution in predators to ongoing climate warming might have indirect cross-generational ecological consequences propagating through food webs.

While it is known that increased dissolved CO 2 concentrations and rising sea surface temperature (ocean warming) can act interactively on marine phytoplankton, the ultimate molecular mechanisms underlying this interaction on a long-term evolutionary scale are relatively unexplored. Here, we performed transcriptomics and quantitative metabolomics analyses, along with a physiological trait analysis, on the marine diatom Thalassiosira weissflogii adapted for approximately 3.5 years to warming and/or high CO 2 conditions. We show that long-term warming has more pronounced impacts than elevated CO 2 on gene expression, resulting in a greater number of differentially expressed genes (DEGs). The largest number of DEGs was observed in populations adapted to warming + high CO 2 , indicating a potential synergistic interaction between these factors. We further identified the metabolic pathways in which the DEGs function and the metabolites with significantly changed abundances. We found that ribosome biosynthesis-related pathways were upregulated to meet the increased material and energy demands after warming or warming in combination with high CO 2 . This resulted in the upregulation of energy metabolism pathways such as glycolysis, photorespiration, the tricarboxylic acid cycle, and the oxidative pentose phosphate pathway, as well as the associated metabolites. These metabolic changes help compensate for reduced photochemical efficiency and photosynthesis. Our study emphasizes that the upregulation of ribosome biosynthesis plays an essential role in facilitating the adaptation of phytoplankton to global ocean changes and elucidates the interactive effects of warming and high CO 2 on the adaptation of marine phytoplankton in the context of global change., (© 2024 Society for Experimental Biology and John Wiley & Sons Ltd.)

Gelatinous zooplankton constitutes a polyphyletic group with a convergent evolutionary history and poorly known biogeographical patterns. In the Gulf of Mexico, a region with complex geological, hydrological, and biotic histories, the study of this group has been limited to taxonomical and ecological aspects. In this study, we implemented a track analysis to identify distributional patterns of gelatinous zooplankton in the Gulf of Mexico and adjacent waters based on a dataset of 6067 occurrence records corresponding to Hydrozoa, Scyphozoa, Cubozoa, Ctenophora, Chaetognatha, Thaliacea, and Appendicularia. Information was compiled from the Global Biodiversity Facility Information (GBIF) and Ocean Biodiversity Information System (OBIS) databases and peer-reviewed literature. Individual tracks were constructed by joining the minimum distance between the occurrence localities of each taxon using a minimum spanning tree algorithm. We identified generalized tracks using parsimony analysis of endemicity with progressive character elimination (PAE-PCE). The areas where different generalized tracks overlapped were considered to represent panbiogeographical nodes. Seven generalized tracks (two with nested patterns) and six panbiogeographical nodes were recognized, mainly in neritic zones. The distributional patterns of gelatinous zooplankton allowed us to identify four biogeographic areas, supporting previously proposed biogeographic schemes. Gelatinous zooplankton in the Gulf of Mexico showed a convergent spatial distribution that can be explained by vicariant and dispersal events. The historical biogeography of the gelatinous biotas of the Gulf of Mexico has been little studied compared to ecological approaches, and the lack of integrative studies considering historical patterns is evident. This type of research is fundamental to understanding the evolutionary history of natural resources from a spatial perspective, identifying sites of biodiversity and endemism, and establishing a biogeographic baseline of the region for further studies., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Ahuatzin-Hernández et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

The broadband scientific echosounder is considered to have great potential for zooplankton monitoring. In this study, two common types of zooplankton in the South China Sea, Rhopilema hispidum and Acetes chinensis , were continuously monitored using a broadband scientific echosounder. The results revealed distinct volume scattering strength (SV) spectral characteristics between the echoes of R. hispidum and A. chinensis . Meanwhile, echoes of R. hispidum and A. chinensis were classified using the k-means clustering algorithm, achieving an 83.4% accuracy rate. The SV value at a nominal frequency of R. hispidum changes more sharply than that of A. chinensis , suggesting that the density of R. hispidum changes more dramatically. This study demonstrates the advantages of monitoring R. hispidum and A. chinensis outbreaks with a broadband scientific echosounder.

Basin-scale patterns of biodiversity for zooplankton in the ocean may provide valuable insights for understanding the impact of climate change and global warming on the marine ecosystem. However, studies on this topic remain scarce or unavailable in vast regions of the world ocean, particularly in large regions where the amount and quality of available data are limited. In this study, we used a 27-year (1993-2019) database on species occurrence of planktonic copepods in the South Pacific, along with associated oceanographic variables, to examine their spatial patterns of biodiversity in the upper 200 m of the ocean. The aim of this study was to identify ecological regions and the environmental predictors explaining such patterns. It was found that hot and cold spots of diversity, and distinctive species assemblages were linked to major ocean currents and large regions over the basin, with increasing species richness over the subtropical areas on the East and West sides of the South Pacific. While applying the spatial models, we showed that the best environmental predictors for diversity and species composition were temperature, salinity, chlorophyll-a concentration, oxygen concentration, and the residual autocorrelation. Nonetheless, the observed spatial patterns and derived environmental effects were found to be strongly influenced by sampling coverage over space and time, revealing a highly under-sampled basin. Our findings provide an assessment of copepods diversity patterns and their potential drivers for the South Pacific Ocean, but they also stress the need for strengthening the data bases of planktonic organisms, as they can act as suitable indicators of ecosystem response to climate change at basin scale., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Pérez-Aragón et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Eukaryotic phytoplankton, also known as algae, form the basis of marine food webs and drive marine carbon sequestration. Algae must regulate their motility and gravitational sinking to balance access to light at the surface and nutrients in deeper layers. However, the regulation of gravitational sinking remains largely unknown, especially in motile species. Here, we quantify gravitational sinking velocities according to Stokes' law in diverse clades of unicellular marine microalgae to reveal the cell size, density, and nutrient dependency of sinking velocities. We identify a motile algal species, Tetraselmis sp., that sinks faster when starved due to a photosynthesis-driven accumulation of carbohydrates and a loss of intracellular water, both of which increase cell density. Moreover, the regulation of cell sinking velocities is connected to proliferation and can respond to multiple nutrients. Overall, our work elucidates how cell size and density respond to environmental conditions to drive the vertical migration of motile algae.

Sea-ice microalgae are a key source of energy and nutrient supply to polar marine food webs, particularly during spring, prior to open-water phytoplankton blooms. The nutritional quality of microalgae as a food source depends on their biomolecular (lipid:protein:carbohydrate) composition. In this study, we used synchrotron-based Fourier transform infra-red microspectroscopy (s-FTIR) to measure the biomolecular content of a dominant sea-ice taxa, Nitzschia frigida, from natural land-fast ice communities throughout the Arctic spring season. Repeated sampling over six weeks from an inner (relatively stable) and an outer (relatively dynamic) fjord site revealed high intra-specific variability in biomolecular content, elucidating the plasticity of N. frigida to adjust to the dynamic sea ice and water conditions. Environmental triggers indicating the end of productivity in the ice and onset of ice melt, including nitrogen limitation and increased water temperature, drove an increase in lipid and fatty acids stores, and a decline in protein and carbohydrate content. In the context of climate change and the predicted Atlantification of the Arctic, dynamic mixing and abrupt warmer water advection could truncate these important end-of-season environmental shifts, causing the algae to be released from the ice prior to adequate lipid storage, influencing carbon transfer through the polar marine system., (© 2024. The Author(s).)

Satellite-derived chlorophyll-a concentration (Chl-a) is essential for assessing environmental conditions, yet its application in the optically complex waters of the eastern Yellow Sea (EYS) is challenged. This study refines the Chl-a algorithm for the EYS employing a switching approach based on normalized water-leaving radiance at 555 nm wavelength according to turbidity conditions to investigate phytoplankton bloom patterns in the EYS. The refined Chl-a algorithm (EYS algorithm) outperforms prior algorithms, exhibiting a strong alignment with in situ Chl-a. Employing the EYS algorithm, seasonal and bloom patterns of Chl-a are detailed for the offshore and nearshore EYS areas. Distinct seasonal Chl-a patterns and factors influencing bloom initiation differed between the areas, and the peak Chl-a during the bloom period from 2018 to 2020 was significantly lower than the average year in both areas. Specifically, bimodal and unimodal peak patterns in Chl-a were observed in the offshore and nearshore areas, respectively. By investigating the relationships between environmental factors and bloom parameters, we identified that major controlling factors governing bloom initiation were mixed layer depth (MLD) and suspended particulate matter (SPM) in the offshore and nearshore areas, respectively. Additionally, this study proposed that the recent decrease in the peak Chl-a might be caused by rapid environmental changes such as the warming trend of sea surface temperature (SST) and the limitation of nutrients. For example, external forcing, phytoplankton growth, and nutrient dynamics can change due to increased SST and limitation of nutrients, which can lead to a decrease in Chl-a. This study contributes to understanding phytoplankton dynamics in the EYS, highlighting the importance of region-specific considerations in comprehending Chl-a patterns and bloom dynamics., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Coastal hypoxia (low dissolved oxygen in seawater) is a cumulative result of many physical and biochemical processes. However, it is often difficult to determine the key drivers of hypoxia due to the lack of frequent observational oceanographic and meteorological data. In this study, high-frequency time-series observational data of dissolved oxygen (DO) and related parameters in the coastal waters of Muping, China, were used to analyze the temporal pattern of hypoxia and its key drivers. Two complete cycles with the formation and destruction of hypoxia were captured over the observational period. Persistent thermal stratification, high winds and phytoplankton blooms are identified as key drivers of hypoxia in this region. Hypoxia largely occurs due to persistent thermal stratification in summer, and hypoxia can be noticeably relieved when strong wind mixing weakens thermal stratification. Furthermore, we found that northerly high winds are more efficient at eroding stratification than southerly winds and thus have a greater ability to relieve hypoxia. This study revealed an episodic hypoxic event driven by a phytoplankton bloom that was probably triggered by terrestrial nutrient loading, confirming the causal relationship between phytoplankton blooms and hypoxia. In addition, we found that the lag time between nutrient loading, phytoplankton blooms and hypoxia can be as short as one week. This study could help better understand the development of hypoxia and forecast phytoplankton and hypoxia, which are beneficial for aquaculture in this region., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

How microzooplanktonic ciliate adaptative strategies differ across diatom bloom and non-diatom bloom areas in the Arctic Ocean remains poorly documented. To address this gap, two different situations were categorized in the Arctic Ocean at summer 2023: diatom bloom stations (DBS) (genus Thalassiosira, chain-like) and non-diatom bloom stations (nDBS). Total abundance of ciliate at 3 m and 25 m in DBS was 2.8 and 1.8 folds higher than in nDBS, respectively. Aloricate ciliates were singled out in both DBS and nDBS, whilst their average abundance and biomass of large size-fraction (>50 μm) in former were 4.5-5.6 folds higher than in latter. Regarding tintinnids, high abundance of Ptychocylis acuta (Bering Strait species) mainly occurred at DBS, coupled with distribution of co-occurring Pacific-origin species Salpingella sp.1, collectively suggested a strong intrusion of Pacific Inflow during summer 2023. Additionally, presence of high abundance of Acanthostomella norvegica and genus Parafavella in nDBS might indicate the trajectory of the Transpolar Drift. Alternatively, tintinnids can serve as credible bioindicators for either monitoring currents or evaluating microzooplankton Borealization. Average abundance of total ciliate within 15-135 μm body-size spectrum in DBS was higher than nDBS. Moreover, spearman's rank correlation between biotic and abiotic analysis revealed that temperature and dissolved oxygen at DBS determined tintinnid species richness and ciliate total abundance, respectively. The results clearly demonstrate that remarkable divergences in large size-fraction of ciliate abundance between DBS and nDBS validate their irreplaceable role in controlling phytoplankton outbreak and associated biological processes in polar seas., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Southern right whales (SRWs, Eubalaena australis) have been observed feeding both at and below the surface (< 10 m) in Golfo Nuevo (42°42' S, 64°30' W), Península Valdés, Argentina, an area traditionally recognized as calving ground. In addition, we documented diving feeding behavior in SRWs during their stay in this gulf, which has not been previously described. We assessed this behavior using suction-cup-attached video-imaging tags (CRITTERCAMs) on individual whales. A total of eight CRITTERCAM deployments were successful, and feeding events were documented in all SRWs successfully equipped with CRITTERCAMs. The highest speeds occurred during the ascent phase, and the average diving time was 6 min 45 s ± 3 min 41 s for SRWs. Concurrently, zooplankton samples were collected from the subsurface and bottom of the water in areas where tagged whales dived to assess differences in composition, abundance, and biomass. Copepods dominated the upper layer, while euphausiids were more abundant in the deeper sample. Furthermore, zooplankton total biomass was five times higher at depth (2515.93 mg/m 3 ) compared to the subsurface (500.35 mg/m 3 ). Differences in zooplankton characteristics between depths, combined with CRITTERCAM videos, indicated that SRWs exploit high concentrations of organisms near the seafloor during daytime feeding dives. This study provides baseline insights into how SRWs utilize Península Valdés during their stay in the area., (© 2024. The Author(s).)

Mycoloop is an important aquatic food web composed of phytoplankton, chytrids (one dominant group of parasites in aquatic ecosystems), and zooplankton. Chytrids infect phytoplankton and fragment them for easy consumption by zooplankton. The free-living chytrid zoospores are also a food resource for zooplankton. A dynamic reaction-diffusion-advection mycoloop model is proposed to describe the Phytoplankton-chytrid-zooplankton interactions in a poorly mixed aquatic environment. We analyze the dynamics of the mycoloop model to obtain dissipativity, steady state solutions, and persistence. We rigorously derive several critical thresholds for phytoplankton or zooplankton invasion and chytrid transmission among phytoplankton. Numerical diagrams show that varying ecological factors affect the formation and breakup of the mycoloop, and zooplankton can inhibit chytrid transmission among phytoplankton. Furthermore, this study suggests that mycoloop may either control or cause phytoplankton blooms., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Warming global temperatures have consequences for biological rates. Feeding rates reflect the intake of energy that fuels survival, growth and reproduction. However, temperature can also affect food abundance and quality, as well as feeding behavior, which all affect feeding rate, making it challenging to understand the pathways by which temperature affects the intake of energy. Therefore, we experimentally assessed how clearance rate varied across a thermal gradient in a filter-feeding colonial marine invertebrate (the bryozoan Bugula neritina). We also assessed how temperature affects phytoplankton as a food source, and zooid states within a colony that affect energy budgets and feeding behavior. Clearance rate increased linearly from 18°C to 32°C, a temperature range that the population experiences most of the year. However, temperature increased algal cell size, and decreased the proportion of feeding zooids, suggesting indirect effects of temperature on clearance rates. Temperature increased polypide regression, possibly as a stress response because satiation occurred quicker, or because phytoplankton quality declined. Temperature had a greater effect on clearance rate per feeding zooid than it did per total zooids. Together, these results suggest that the effect of temperature on clearance rate at the colony level is not just the outcome of individual zooids feeding more in direct response to temperature but also emerges from temperature increasing polypide regression and the remaining zooids increasing their feeding rates in response. Our study highlights some of the challenges for understanding why temperature affects feeding rates, especially for understudied, yet ecologically important, marine colonial organisms., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Understanding the relative role of dispersal dynamics and niche constraints is not only a core task in community ecology, but also becomes an important prerequisite for bioassessment. Despite the recent progress in our knowledge of community assembly in space and time, patterns and processes underlying biotic communities in alpine glacierized catchments remain mostly ignored. To fill this knowledge gap, we combined the recently proposed dispersal-niche continuum index (DNCI) with traditional constrained ordinations and idealized patterns of species distributions to unravel community assembly mechanisms of different key groups of primary producers and consumers (i.e., phytoplankton, epiphytic algae, zooplankton, macroinvertebrates, and fishes) in rivers in the Qinghai-Tibet Plateau, the World's Third Pole. We tested whether organismal groups with contrasting body sizes differed in their assembly processes, and discussed their applicability in bioassessment in alpine zones. We found that community structure of alpine river biotas was always predominantly explained in terms of dispersal dynamics and historical biogeography. These patterns are most likely the result of differences in species-specific functional attributes, the stochastic colonization-extinction dynamics driven by multi-year glacier disturbances and the repeated hydrodynamic separation among alpine catchments after the rising of the Qilian mountains. Additionally, we found that the strength of dispersal dynamics and niche constraints was partially mediated by organismal body sizes, with dispersal processes being more influential for microscopic primary producers. Finding that zooplankton and macroinvertebrate communities followed clumped species replacement structures (i.e., Clementsian gradients) supports the notion that environmental filtering also contributes to the structure of high-altitude animal communities in glacierized catchments. In terms of the applied fields, we argue that freshwater bioassessment in glacierized catchments can benefit from incorporating the metacommunity perspective and applying novel approaches to (i) detect the optimal spatial scale for species sorting and (ii) identify and eliminate the species that are sensitive to dispersal-related processes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Aquatic macrophytes form a three dimensional complex structure in the littoral zones of lakes, with many physical, chemical and biological gradients and interactions. This special habitat harbours a unique microalgal assemblage called metaphyton, that differs both from the phytoplankton of the pelagial and from the benthic assemblages whose elements are tightly attached to the substrates. Since metaphytic assemblages significantly contribute to the diversity of lakes' phytoplankton, it is crucial to understand and disentangle those mechanisms that ensure their development. Therefore, we focused on the question of how a single solid physical structure contribute to maintaining metaphytic assemblages. Using a laboratory experiment we studied the floristic and functional differences of microalgal assemblages in microcosms that simulated the conditions that an open water, a complex natural macrophyte stand (Utricularia vulgaris L.), or an artificial substrate (cotton wool) provide for them. We inoculated the systems with a species rich (> 326 species) microalgal assemblage collected from a eutrophic oxbow lake, and studied the diversity, trait and functional group composition of the assemblages in a 24 day long experimental period. We found that both natural and artificial substrates ensured higher species richness than the open water environment. Functional richness in the open water environment was lower than in the aquaria containing natural macrophyte stand but higher than in which cotton wool was placed. This means that the artificial physical structure enhanced functional redundancy of the resident functional groups. Elongation measures of microalgal assemblages showed the highest variation in the microcosms that simulated the open water environment. Our results suggest that assembly of metaphytic algal communities is not a random process, instead a deterministic one driven by the niche characteristics of the complex three dimensional structure created by the stands of aquatic macrophytes., (© 2024. The Author(s).)

Bioluminescence is light chemically produced by an organism. It is widespread across all major marine phyla and has evolved multiple times, resulting in a high diversity of spectral properties and first flash kinetic parameters (FFKP). The bioluminescence of a system is often a good proxy for planktonic biomass. The species-specific parameters of bioluminescent displays can be measured to identify species in situ and describe planktonic biodiversity. Most bioluminescent organisms will flash when mechanically stimulated i.e. , when subjected to supra-threshold levels of shear stress. Here we compare first flash kinetic parameters such as flash duration, peak intensity, rise time, decay time, first-flash mechanically stimulated light and e-folding time obtained with the commercially available Underwater Bioluminescence Assessment Tool (UBAT). We provide descriptions of the first flash kinetic parameters of several species of dinoflagellates Pyrocystis fusiformis , Pyrocystis noctiluca , Pyrodinium bahamense , Lingulodinium polyedra , Alexandrium monilatum and two zooplankton (the ctenophore Mnemiopsis leidyi and the larvacean Oikopleura sp. ). FFKPs are then compared and discussed using non-parametric analyses of variance (ANOVAs), hierarchical clustering and a linear discriminant analysis to assess the ability to use bioluminescence signatures for identification. Once the first flash kinetic parameters of a bioluminescent species have been described, it is possible to detect its presence using emissions collected by in situ bathyphotometers. Assessing abundance and diversity of bioluminescent species may therefore be possible., Competing Interests: The authors declare there are no competing interests., (©2024 Letendre et al.)

There is a growing interest in the impact of acoustic pollution on aquatic ecosystems. Currently, research has primarily focused on hearing species, particularly fishes and mammals. However, species from lower trophic levels, including many invertebrates, are less studied despite their ecological significance. Among these taxa, studies examining the effects of sound on holozooplankton are extremely rare. This literature review examines the effects of sound on both marine and freshwater zooplankton. It highlights two differences: the few used organisms and the types of sound source. Marine studies focus on the effects of very intense acute sound on copepods, while freshwater studies focus on less intense chronic sound on cladocerans. But, in both, various negative effects are reported. The effects of sound remain largely unknown, although previous studies have shown that zooplankton can detect vibrations using mechanoreceptors. The perception of their environment can be affected by sounds, potentially causing stress. Limited research suggests that sound may affect the physiology, behaviour, and fitness of zooplankton. Following this review, I highlight the potential to use methods from ecology, ecotoxicology, and parasitology to study the effects of sound at the individual level, including changes in physiology, development, survival, and behaviour. Responses to sound, which could alter species interactions and population dynamics, are expected to have larger-scale implications with bottom-up effects, such as changes in food web dynamics and ecosystem functioning. To improve the study of the effect of sound, to better use zooplankton as biological models and as bioindicators, researchers need to better understand how they perceive their acoustic environment. Consequently, an important challenge is the measurement of particle motion to establish useable dose-response relationships and particle motion soundscapes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

Oceanic eddies are recognized as pivotal components in marine ecosystems, believed to concentrate a wide range of marine life spanning from phytoplankton to top predators. Previous studies have posited that marine predators are drawn to these eddies due to an aggregation of their forage fauna. In this study, we examine the response of forage fauna, detected by shipboard acoustics, across a broad sample of a thousand eddies across the world's oceans. While our findings show an impact of eddies on surface temperatures and phytoplankton in most cases, they reveal that only a minority (13%) exhibit significant effects on forage fauna, with only 6% demonstrating an oasis effect. We also show that an oasis effect can occur both in anticyclonic and cyclonic eddies, and that the few high-impact eddies are marked by high eddy amplitude and strong water-mass-trapping. Our study underscores the nuanced and complex nature of the aggregating role of oceanic eddies, highlighting the need for further research to elucidate how these structures attract marine predators., (© 2024. The Author(s).)

The bloom-forming species Microcystis wesenbergii and M. aeruginosa occur in many lakes globally, and may exhibit alternating blooms both spatially and temporally. As environmental changes increase, cyanobacteria bloom in more and more lakes and are often dominated by M. wesenbergii. The adverse impact of M. aeruginosa on co-existing organisms including zooplanktonic species has been well-studied, whereas studies of M. wesenbergii are limited. To compare effects of these two species on zooplankton, we explored effects of exudates from different strains of microcystin-producing M. aeruginosa (Ma905 and Ma526) and non-microcystin-producing M. wesenbergii (Mw908 and Mw929), on reproduction by the model zooplankter Daphnia magna in both chronic and acute exposure experiments. Specifically, we tested physiological, biochemical, molecular and transcriptomic characteristics of D. magna exposed to Microcystis exudates. We observed that body length and egg and offspring number of the daphnid increased in all treatments. Among the four strains tested, Ma526 enhanced the size of the first brood, as well as total egg and offspring number. Microcystis exudates stimulated expression of specific genes that induced ecdysone, juvenile hormone, triacylglycerol and vitellogenin biosynthesis, which, in turn, enhanced egg and offspring production of D. magna. Even though all strains of Microcystis affected growth and reproduction, large numbers of downregulated genes involving many essential pathways indicated that the Ma905 strain might contemporaneously induce damage in D. magna. Our study highlights the necessity of including M. wesenbergii into the ecological risk evaluation of cyanobacteria blooms, and emphasizes that consequences to zooplankton may not be clear-cut when assessments are based upon production of microcystins alone., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Runbing Xu reports financial support was provided by National Natural Science Foundation of China. Xuexiu Chang reports financial support was provided by National Natural Science Foundation of China. Runbing Xu reports financial support was provided by Yunnan Applied Basic Research Project. Xuexiu Chang reports financial support was provided by Yunnan Applied Basic Research Project. Xuexiu Chang reports financial support was provided by Yunnan Provincial Department of Education. Xuexiu Chang reports financial support was provided by Natural Sciences and Engineering Research Council of Canada. Hugh J. MacIsaac reports financial support was provided by Natural Sciences and Engineering Research Council of Canada. Hugh J. MacIsaac reports financial support was provided by Canada Research Chair. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Global climate change intensifies the water cycle and makes freshest waters become fresher and vice-versa. But how this change impacts phytoplankton in coastal, particularly harmful algal blooms (HABs), remains poorly understood. Here, we monitored a coastal bay for a decade and found a significant correlation between salinity decline and the increase of Karenia mikimotoi blooms. To examine the physiological linkage between salinity decreases and K. mikimotoi blooms, we compare chemical, physiological and multi-omic profiles of this species in laboratory cultures under high (33) and low (25) salinities. Under low salinity, photosynthetic efficiency and capacity as well as growth rate and cellular protein content were significantly higher than that under high salinity. More strikingly, the omics data show that low salinity activated the glyoxylate shunt to bypass the decarboxylation reaction in the tricarboxylic acid cycle, hence redirecting carbon from CO 2 release to biosynthesis. Furthermore, the enhanced glyoxylate cycle could promote hydrogen peroxide metabolism, consistent with the detected decrease in reactive oxygen species. These findings suggest that salinity declines can reprogram metabolism to enhance cell proliferation, thus promoting bloom formation in HAB species like K. mikimotoi, which has important ecological implications for future climate-driven salinity declines in the coastal ocean with respect to HAB outbreaks., (© 2024 John Wiley & Sons Ltd.)

Sandusky Bay is the drowned mouth of the Sandusky River in the southwestern portion of Lake Erie. The bay is a popular recreation location and a regional source for drinking water. Like the western basin of Lake Erie, Sandusky Bay is known for being host to summer cyanobacterial harmful algal blooms (cHABs) year after year, fueled by runoff from the predominantly agricultural watershed and internal loading of legacy nutrients (primarily phosphorus). Since at least 2003, Sandusky Bay has harbored a microcystin-producing bloom of Planktothrix agardhii, a species of filamentous cyanobacteria that thrives in low light conditions. Long-term sampling (2003-2018) of Sandusky Bay revealed regular Planktothrix-dominated blooms during the summer months, but in recent years (2019-2022), 16S rRNA gene community profiling revealed that Planktothrix has largely disappeared. From 2017-2022, microcystin decreased well below the World Health Organization (WHO) guidelines. Spring TN:TP ratios increased in years following dam removal, yet there were no statistically significant shifts in other physicochemical variables, such as water temperature and water clarity. With the exception of the high bloom of Planktothrix in 2018, there was no statistical difference in chlorophyll during all other years. Concurrent with the disappearance of Planktothrix, Cyanobium spp. have become the dominant cyanobacterial group. The appearance of other potential toxigenic genera (i.e., Aphanizomenon, Dolichospermum, Cylindrospermopsis) may motivate monitoring of new toxins of concern in Sandusky Bay. Here, we document the regime shift in the cyanobacterial community and propose evidence supporting the hypothesis that the decline in the Planktothrix bloom was linked to the removal of an upstream dam on the Sandusky River., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

Neuston, situated at the air-sea interface, stands as a crucial frontier in the realm of the global warming. Despite its unique habitat, there remains a need to substantiate the composition, diel dynamic and biotic-abiotic interaction of neustonic zooplankton in the tropical seas. In this study, we present rare observational data on neustonic zooplankton (0-20 cm) in the oligotrophic tropical South China Sea (SCS) during the summer of 2022. A total of eighteen samples were collected and analyzed, revealing the presence of fourteen taxa from eight phyla. The most prevalent group was Cypridina, accounting for 33.7% of the total abundance, followed by copepods (29.0%) and jellyfish (10.9%). Within copepods, the genus Pontella exhibited the highest relative abundance (38.0%). Additionally, each neuston taxon displayed unique diel distribution patterns. Cypridina was the most abundant taxon during the night (40.4%), while it shifted to copepod dominance during the day (50.4%). Among copepods, genus Pontella and larvae were dominant groups at night (44.7%) and during the day (30.0%), respectively. Moreover, a multivariate biota-environment analysis demonstrated that temperature, pH, dissolved oxygen and Si(OH) 4 significantly impacted neuston composition. Notably, both jellyfish and sea snails showed a significant positive correlation with temperature, suggesting their potential dominance in the neuston community in response to future global warming in the oligotrophic tropical seas. This study lays a robust foundation for recognizing the neuston community in the oceanic SCS, and helps evaluate the long-term risks to neuston habitats under climate changes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

In this study, two different approaches based on taxonomic assemblages and on copepod functional groups were used to investigate the mesozooplankton assemblage structure and its relationship with environmental variables in the main estuaries of the Gulf of Cádiz (Guadalquivir, Guadiana and Tinto-Odiel) during the dry-warm season. In general, the mesozooplankton assemblages were dominated by copepods, especially the calanoid Acartia tonsa, which reached its highest abundance in the inner zones while the adjacent coastal zones were characterized by a mixture of copepods and cladocerans, especially Penilia avirostris. Regarding the trait-based approach, three copepod functional groups were identified, principally sorted by their feeding strategy. Group 1 (composed of omnivorous copepods displaying a mixed feeding strategy and broadcast-spawners) was found mainly in the inner areas, while Groups 2 (omnivorous cyclopoids, sac-spawners that feed via active ambush) and 3 (herbivores-omnivores employing a filter feeding strategy and mostly broadcast-spawners) were predominant in the adjacent coastal zones. The relative abundance of copepod functional groups suggested that Group 1 could be considered the most important contributor to secondary production in the estuarine systems of the Gulf of Cádiz. In relation to environmental factors, salinity was the most influential variable on mesozooplankton assemblages in both approaches. Our results suggest that the studied estuaries, although taxonomically different, have mesozooplankton assemblages that perform similar ecological functions. Both methods provide valuable and complementary information about mesozooplankton assemblage dynamics in the main estuaries of the Gulf of Cádiz., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Human activities and climate change cause abiotic factors to fluctuate through time, sometimes passing thresholds for organismal reproduction and survival. Multiple stressors can independently or interactively impact organisms; however, few studies have examined how they interact when they overlap spatially but occur asynchronously. Fluctuations in salinity have been found in freshwater habitats worldwide. Meanwhile, heatwaves have become more frequent and extreme. High salinity pulses and heatwaves are often decoupled in time but can still collectively impact freshwater zooplankton. The time intervals between them, during which population growth and community recovery could happen, can influence combined effects, but no one has examined these effects. We conducted a mesocosm experiment to examine how different recovery times (0-, 3-, 6-week) between salt treatment and heatwave exposure influence their combined effects. We hypothesized that antagonistic effects would appear when having short recovery time, because previous study found that similar species were affected by the two stressors, but effects would become additive with longer recovery time since fully recovered communities would respond to heatwave similar to undisturbed communities. Our findings showed that, when combined, the two-stressor joint impacts changed from antagonistic to additive with increased recovery time between stressors. Surprisingly, full compositional recovery was not achieved despite a recovery period that was long enough for population growth, suggesting legacy effects from earlier treatment. The recovery was mainly driven by small organisms, such as rotifers and small cladocerans. As a result, communities recovering from previous salt exposure responded differently to heatwaves than undisturbed communities, leading to similar zooplankton communities regardless of the recovery time between stressors. Our research bolsters the understanding and management of multiple-stressor issues by revealing that prior exposure to one stressor has long-lasting impacts on community recovery that can lead to unexpected joint effects of multiple stressors., (© 2024 The Author(s). Global Change Biology published by John Wiley & Sons Ltd.)

A digestibility enhancing effect of natural food on stomachless fish model (Cyprinus carpio) was verified by fluorogenic substrate assays of enzymatic activities in experimental pond carp gut flush and planktonic food over a full vegetative season. Then compared with size-matched conspecific grown artificially (tank carp) and an advanced omnivore species possessing true stomach (tilapia, Oreochromis niloticus). Results suggested activities of digestive enzymes (except amylolytic) were significantly higher in pond carp (p ≤ 0.05) than in the size-matched tank carp. Even compared to tilapia, pond carp appeared superior (p < 0.05; proteolytic or chitinolytic activities) or comparable (p > 0.05; phosphatase or cellulolytic activities). Amylolytic, chitinolytic, and phosphatases activities in pond carp gut significantly increased (p ≤ 0.01) over season. Several orders-of-magnitude higher enzymatic activities were detected in planktonic natural food than expressed in carp gut. Amino acid markers in planktonic food revealed a higher share of zooplankton (microcrustaceans), but not phytoplankton, synchronized with higher activities of complex polysaccharide-splitting enzymes (cellulolytic and chitinolytic) in fish gut. Periods of clear water phase low in chlorophyll-a and nutrients, but high in certain zooplankton (preferably cladocerans), may create a synergistic digestibility effect in pond carp. We conclude aquatic ecosystem components (natural food, water, microbiota) enhance fishes' hydrolyzing capabilities of C/N/P macromolecules and even their complex polymers such as cellulose, chitin, and maybe phytate (to be validated), to the extent that being stomachless is not an issue. Aquatic nutritional ecologists may consider that laboratory-based understandings of digestibility may underestimate digestion efficiency of free-ranging fish in ponds or lakes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The study examines the complex impact of climatic patterns, driven by the North Atlantic Oscillation (NAO), on regional climate, hydrology, and sea surface temperatures. Focused on the period from 2003 to 2012, the research specifically investigates the influence of thermal variability on decapod larval communities. Monthly zooplanktonic sampling conducted at the Mondego Estuary, Portugal, entrance over a decade revealed the prevalence of Carcinus maenas, Diogenes pugilator, and Pachigrapsus marmoratus larvae. These assemblages displayed notable interannual and seasonal fluctuations, often corresponding with changes in sea surface temperatures. Significant system shifts around 2007, instigated by the large-scale NAO, led to subsequent modifications in sea surface temperature and decapod larvae communities' dynamics. Post-2007, there was an upward trajectory in both species' abundance and richness. Phenologically during the former period, the community exhibited two abundance peaks, with the earlier peak occurring sooner, attributed to heightened temperatures instead of the unique peak exhibited before 2007. The research further elucidated the occurrences of Marine Heatwaves (MHW) in the region, delving into their temporal progression influenced by the NAO. Although water temperature emerged as a crucial factor influencing decapod larvae communities annually and seasonally, the study did not observe discernible impacts of MHW events on these communities. These communities represent essential trophic links and are crucial for the survival success of adult decapods. Given the rapid pace of climate change and increasing temperatures, it is imperative to assess whether these environmental shifts, particularly in thermal conditions, affect these meroplanktonic communities., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

In August 2018, the harmful algae species Margalefidinium polykrikoides bloomed to levels previously unobserved in the open waters of Narragansett Bay, Rhode Island, in a transient but intense bloom. Detected by an Imaging FlowCytobot providing hourly data, it is characterized by a time span of less than a week and patchiness with sub-daily oscillations in concentration. The highest concentrations are recorded at lower salinity and higher temperature, suggesting the bloom may have developed in the upper bay and was transported south. The proportion of chains increased during the height of the bloom, and many of the images contained 4-cells per chain. The development of the bloom was favored by optimal temperature and salinity conditions as well as increased nitrogen coincident with greater precipitation and river flow. The period preceding bloom formation also saw a sharp decrease in the dominating large chain-forming diatom Eucampia sp. and highly abundant Skeletonema spp., thus reducing competition over resources for the slow-growing M. polykrikoides. The height of the bloom was reached during the lowest tidal range of the month when the turbulence and water displacement were lower. This time series highlights an out-of-the-ordinary bloom's environmental and biological conditions and the importance of frequent sampling during known favorable conditions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

In this study, we investigated the hydrological and ecological impacts of heavy rainfall caused by the storm Rumbia and Typhoon Lekima on Laizhou Bay (LZB) through land‒sea synchronous field surveys, online remote sensors, and simulated enclosure experiments. Within two weeks of Rumbia, approximately 9% and 16% of the annual riverine total nitrogen (TN) and total phosphorus (TP) fluxes, respectively, were transported to the LZB and the proportions were 17% and 35%, respectively, for Lekima. The land use on the watersheds increased the rates of land-derived nutrient loading and altered their biogeochemical forms. Consequently, the average concentrations of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) in the LZB increased by 2.6 and 1.0 times post-Rumbia and by 3.5 and 1.3 times post-Lekima, respectively. Relatively lower salinity and temperature, sudden increases in DIN, and strengthened coastal currents stimulated the growth of highly adaptable and small diatoms, resulting in the first diatom blooms. Subsequently, a bloom of Noctiluca scintillans formed., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

This paper reports an important conclusion that self-diffusion is not a necessary condition for inducing Turing patterns, while taxis could establish complex pattern phenomena. We investigate pattern formation in a zooplankton-phytoplankton model incorporating phytoplankton-taxis, where phytoplankton-taxis describes the zooplankton that tends to move toward the high-densities region of the phytoplankton population. By using the phytoplankton-taxis sensitivity coefficient as the Turing instability threshold, one shows that the model exhibits Turing instability only when repulsive phytoplankton-taxis is added into the system, while the attractive-type phytoplankton-taxis cannot induce Turing instability of the system. In addition, the system does not exhibit Turing instability when the phytoplankton-taxis disappears. Numerically, we display the complex patterns in 1D, 2D domains and on spherical and zebra surfaces, respectively. In summary, our results indicate that the phytoplankton-taxis plays a pivotal role in giving rise to the Turing pattern formation of the model. Additionally, these theoretical and numerical results contribute to our understanding of the complex interaction dynamics between zooplankton and phytoplankton populations., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

This study analyses over a decade (2009-2022) of monitoring data to understand the impact of hydrological characteristics on water quality and phytoplankton dynamics in Prospect Reservoir, a critical water supply for Greater Sydney, Australia, known for its excellent water quality. Water quality and phytoplankton dynamics were related to hydrodynamics, linked to flow management and the water quality of inflows. Phytoplankton biovolume increased after a prolonged drawdown and subsequent refill event, mainly driven by dinoflagellates, and corresponded to increases in total phosphorus and water temperature. The hydrological period following the 2019/2020 summer bushfires (post-bushfire) that impacted connected reservoirs, was marked by increased flow activity and nutrient loading, leading to significant shifts in the phytoplankton community. Functional group classification and ordination analysis indicated a transition from taxa typically dominant in oligotrophic conditions to meso‑eutrophic. This transition correlated with elevated nutrient levels and chlorophyll-a (Chl-a), and reduced Secchi depth and dissolved oxygen, providing evidence of eutrophication. Q index indicated good water quality post-bushfire, contrasting with a eutrophic status assessment using Chl-a. Our findings highlight the importance of analysing long-term datasets encompassing varied hydroclimatological conditions for a deeper understanding of reservoir behaviour. A comprehensive approach to water quality assessment is recommended, combining functional group classification, Q index and Chl-a measurements for effective reservoir health assessment. This research provides novel insights into the effects of disturbances such as bushfires, on water quality and phytoplankton dynamics in an underrepresented geographic region, offering valuable knowledge for managing water resources amidst growing climate variability., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Huy A. Luong reports financial support was provided by WaterNSW. Huy A. Luong reports financial support was provided by Commonwealth of Australia. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Diurnal vertical migration (DVM) of mesozooplankton in the Deep Scattering Layer (DSL) of the Indian seas is poorly studied. This cyclical vertical migration substantially controls the carbon sequestration in the ocean. The present research is a comprehensive examination to analyse the factors affecting the DVM pattern of the zooplankton community in the Arabian Sea (AS) and the Bay of Bengal (BoB). Echo sounder profiling was conducted at shallow depths (∼10-400m) of the AS (January 2023) and BoB (March 2023) with a period of 24 h to monitor the DVM pattern of the DSL. Vertical migration in both basins showcased the notable influence of the spatio-temporal contrast in the occurrence of daybreak, with the day (descend) and night (ascend) cycle of the DSL. Delayed descent was observed in the AS contrary to BoB, owing to the delayed day break in the AS relative to BoB. Intensity and temporal pattern of the incoming solar radiation were correlated with the DVM whereas diurnal variation of sea surface temperature was observed to be contrasting. The preliminary analysis is indicative of the diversified community structure of the zooplankton community in these basins resulting from the vertical migration. Furthermore, it is conclusive that the surface residence time of the zooplankton is distinct and is affirmed based on daybreak and light intensity particular for each basin. Since daybreak vary with the geolocation, sole dependence on a particular time for migration study can be erroneous, which is highlighted in the present study., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The responses of Phytoplankton Size Classes (PSCs) to seasons and the distinct phases of coastal upwelling in the northern Indian Ocean is an understudied aspect. This study introduces observations from a monthly time series conducted at three cross-shore transects in the south, central, and north regions between 6 and 13°N along the southwest coast of India in the Southeastern Arabian Sea (SEAS). The data represent pre-upwelling (late April to early May), early upwelling (early to mid-June), peak upwelling (early to mid-August), late upwelling (mid to late September), and post-upwelling (late October to early November) phases. The pre-upwelling had a stratified and nitrate-depleted upper euphotic column due to the intrusion of low saline Bay of Bengal water and solar heating which resulted in a low phytoplankton biomass (chlorophyll-a) contributed by pico-PSC (av. 56.21 ± 21.23 %) followed by nano-PSC (25.25 ± 5.98 %). During the early upwelling, a dominant micro-PSC was prevalent in the coastal stations in the south transect due to the initiation of upwelling there. The peak upwelling was characterised by significant nutrient enrichment causing the dominance of larger micro- and meso-PSCs in the entire coastal region (av. 79.13 ± 39.68 %). Since the late upwelling had less nutrient enrichment, the contribution of nano- and pico-PSCs increased along the south and central transects. By the post-upwelling phase, the dominance of nano-PSC (av. 57.85 ± 11.02 %) and pico-PSC (av. 21.19 ± 11.72 %) was reestablished in the study area due to the end of the nutrient enrichment of upwelling. The subsurface chlorophyll maxima, which was found below 50 m during the pre-upwelling phase, had altered into a thick layer (30 m) and shifted to the upper water column during the upwelling phases when nutrients were higher and solar radiation was lower in the surface waters. A sequential transition of PSCs from pre-upwelling to post-upwelling was evident and it appears that the very high supply of nutrients NO 3 and SiO 4 (>5 μM) during different phases of upwelling favoured the dominance of larger PSCs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Diatoms and dinoflagellates are two typical functional groups of phytoplankton assemblages, which play a crucial role in the structure and functioning of most marine ecosystems. To date, a novel challenge in ecology and biogeochemistry is to address the influences of environmental changes associated with climate change and human activities on the dynamics of diatoms and dinoflagellates. However, the knowledge of the key environmental factors controlling the diatom-dinoflagellate dynamics remains to be improved, particularly in the coastal ecosystems. Therefore, we conducted four cruises along the Qingdao coastline in spring, summer, autumn, and winter 2022 to explore how diatoms and dinoflagellates varied in response to regional environmental changes. The results showed that the phytoplankton communities were dominated by diatoms and dinoflagellates in terms of abundance and species diversity throughout the year in the study region. Yet, there were significant seasonal variability of diatoms and dinoflagellates across the four seasons. For example, diatom species was the most diverse during autumn, and the higher average abundance was observed in the fall and winter. In contrast, the average abundance of dinoflagellates was maximum during the summer and minimum in the autumn season. Moreover, the abundance and species ratios of diatoms/dinoflagellates (dia/dino) also showed significant seasonal variations in the region. The dia/dino abundance ratio was lowest in summer, while the dia/dino species ratio showed an increasing trend from spring to fall and a slight descending trend during winter. Based on the redundancy analysis, we revealed that diatoms and dinoflagellates responded differently to various environmental variables in different seasons, of which temperature and nutrients (especially dissolved inorganic nitrogen, DIN) had highly significant correlations with both the dia/dino abundance and species ratios. Thus, we suggested that temperature and DIN were the key factors controlling the seasonal dynamics of diatoms and dinoflagellates in the Qingdao coastal area., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Perfluoroalkyl substances (PFAS) are of great ecological concern, however, exploration of their impact on bacteria-phytoplankton consortia is limited. This study employed a bioassay approach to investigate the effect of unary exposures of increasing concentrations of PFAS (perfluorooctane sulfonate (PFOS) and 6:2 fluorotelomer sulfonate (6:2 FTS)) on microbial communities from the northwestern Gulf of Mexico. Each community was examined for changes in growth and photophysiology, exudate production and shifts in community structure (16S and 18S rRNA genes). 6:2 FTS did not alter the growth or health of phytoplankton communities, as there were no changes relative to the controls (no PFOS added). On the other hand, PFOS elicited significant phototoxicity (p < 0.05), altering PSII antennae size, lowering PSII connectivity, and decreasing photosynthetic efficiency over the incubation (four days). PFOS induced a cellular protective response, indicated by significant increases (p < 0.001) in the release of transparent exopolymer particles (TEP) compared to the control. Eukaryotic communities (18S rRNA gene) changed substantially (p < 0.05) and to a greater extent than prokaryotic communities (16S rRNA gene) in PFOS treatments. Community shifts were concentration-dependent for eukaryotes, with the low treatment (5 mg/L PFOS) dominated by Coscinodiscophyceae (40 %), and the high treatment (30 mg/L PFOS) marked by a Trebouxiophyceae (50 %) dominance. Prokaryotic community shifts were not concentration dependent, as both treatment levels became depleted in Cyanobacteriia and were dominated by members of the Bacteroidia, Gammaproteobacteria, and Alphaproteobacteria classes. Further, PFOS significantly decreased (p < 0.05) the Shannon diversity and Pielou's evenness across treatments for eukaryotes, and in the low treatment (5 mg/L PFOS) for prokaryotes. These findings show that photophysiology was not impacted by 6:2 FTS but PFOS elicited toxicity that impacted photosynthesis, exudate release, and community composition. This research is crucial in understanding how PFOS impacts microbial communities., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Phytoplankton is of utmost importance to the marine ecosystem and, subsequently, to the Blue Economy. This study aims to explain the reasons for variability of phytoplankton by estimating the dependency of Chlorophyll-a (Chl-a) on various limiting factors using statistics. The global oceans are classified into coherent units that display similar sensitivity to changing parameters and processes using the k-means algorithm. The resulting six clusters are based on the limiting factors (PAR, iron, or nitrate) that modulate Chl-a yield divisions of the oceans, similar to regions of different trophic statuses. The clusters range from the polar and equatorial regions with high nutrient values limited by light, to open oceanic regions in downwelling gyres limited by nutrients. Some clusters also show a high dependency on marine dissolved iron. Further, oceans are also divided into eight clusters based on the processes (stratification, upwelling, topography, and solar insolation) that impact ocean productivity. The study shows that considering temporal variations is crucial for segregating oceans into ecological zones by utilizing correlation of time-series data into classification. Our results provide valuable insights into the regulation of phytoplankton abundance and its variability, which can help in understanding the implications of climate change and other anthropogenic effects on marine biology., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The Inner Saronikos Gulf has served as an area of continuous environmental monitoring for many decades, primarily due to the operation of primary and secondary sewage treatment facilities of the Psyttalia Waste Water Treatment Plant (WWTP). In this groundbreaking study within the region, we conducted measurements of biochemical indices related to respiration (referred to as spETS) and growth (referred to as spAARS) of mesozooplankton. These measurements were then correlated with both biological and environmental data. The ecological quality of the inner Saronikos Gulf was ameliorated moving away from the sewage outfall and thus mesozooplankton sampling encompassed various sites located across a trophic gradient from the WWTP during different seasons (May, September, November 2017, and January 2018). Our observations revealed seasonal variations in both zooplankton abundance and composition, alongside spatial disparities in environmental data. In terms of biochemical data, we observed significant seasonal fluctuations in spETS and R respiration values. Notably, the lowest respiration R value (0.22 mg C m⁻³ d⁻ 1 ) was recorded in May, while the highest (4.74 mg C m⁻³ d⁻ 1 ) was observed in September. Nevertheless, the variations in spETS and spAARS values among different sites did not demonstrate statistically significant differences. Furthermore, the values of these indices (spETS and spAARS) exhibit a positive correlation with temperature and mesozooplankton biomass at a significance level of 0.01. Lastly, it is noteworthy that phytoplankton production, measured in terms of carbon content (mg C m⁻ 2 ), appeared to adequately meet the carbon requirements of the zooplankton throughout all the examined months., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Phytoplankton bloom received considerable attention for many decades. Different approaches have been used to explain the bloom phenomena. In this paper, we study a Nutrient-Phytoplankton-Zooplankton (NPZ) model consisting of a periodic driving force in the growth rate of phytoplankton due to solar radiation and analyse the dynamics of the corresponding autonomous and non-autonomous systems in different parametric regions. Then we introduce a novel aspect to extend the model by incorporating another periodic driving force into the growth term of the phytoplankton due to sea surface temperature (SST), a key point of innovation. Temperature dependency of the maximum growth rate (μ max ) of the phytoplankton is modelled by the well-known Q 10 formulation: [Formula: see text] , where μ 0 is maximum growth at 0 o C. Stability conditions for all three equilibrium points are expressed in terms of the new parameter ρ 2 , which appears due to the incorporation of periodic driving forces. System dynamics is explored through a detailed bifurcation analysis, both mathematically and numerically, with respect to the light and temperature dependent phytoplankton growth response. Bloom phenomenon is explained by the saddle point bloom mechanism even when the co-existing equilibrium point does not exist for some values of ρ 2 . Solar radiation and SST are modelled using sinusoidal functions constructed from satellite data. Our results of the proposed model describe the initiation of the phytoplankton bloom better than an existing model for the region 25-35° W, 40-45° N of the North Atlantic Ocean. An improvement of 14 days (approximately) is observed in the bloom initiation time. The rate of change method (ROC) is applied to predict the bloom initiation., Competing Interests: Declaration of competing interest On behalf of all authors, I certify that all authors have seen and approved the final version of this revised manuscript. They warrant that the article is the authors’ original work, has not received prior publication and is not under consideration for publication elsewhere. We have no conflicts of interest to disclose., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Phytoplankton Chl:C:N:P ratios are important from both an ecological and a biogeochemical perspective. We show that these elemental ratios can be represented by a phytoplankton physiological model of low complexity that includes major cellular macromolecular pools. In particular, our model resolves time-dependent intracellular pools of chlorophyll, proteins, nucleic acids, carbohydrates/lipids, and N and P storage. Batch culture data for two diatom and two prasinophyte species are used to constrain parameters that represent specific allocation traits and strategies. A key novelty is the simultaneous estimation of physiological parameters for two phytoplankton groups of such different sizes. The number of free parameters is reduced by assuming (i) allometric scaling for maximum uptake rates, (ii) shared half-saturation constants for synthesis of functional macromolecules, (iii) shared exudation rates of functional macromolecules across the species. The rationale behind this assumption is that across the different species, the same or similar processes, enzymes, and metabolites play a role in key physiological processes. For the turnover numbers of macromolecular synthesis and storage exudation rates, differences between diatoms and prasinophytes need to be taken into account to obtain a good fit. Our model fits suggest that the parameters related to storage dynamics dominate the differences in the C:N:P ratios between the different phytoplankton groups. Since descriptions of storage dynamics are still incomplete and imprecise, predictions of C:N:P ratios by phytoplankton models likely have a large uncertainty. • Dynamic phytoplankton physiology model includes major cellular macromolecular pools. • The model fits batch-culture data for two diatom and two prasinophyte species. • Key interspecies differences can be captured using allometrically scaled parameters. • Variations in algal C:N:P ratios are driven by differences in intracellular storage. • Interspecies differences in storage dynamics are not captured by allometric scaling. [ABSTRACT FROM AUTHOR]

Small and shallow water bodies are particularly sensitive to adverse conditions connected with anthropogenic eutrophication. As model systems, ponds are a good object for ecological research and monitoring of global environmental changes. We examined cyanobacteria along with other groups of algae versus zooplankton and abiotic characteristics of water in 51 aquatic ecosystems exposed to anthropogenic pressure (from natural forest to highly disturbed field ponds) with 3 distinct trophic groups: meso-, eu- and hypertrophic. This study aimed to define how different levels of trophy affect pond-specific cyanobacteria assemblages and to identify species responding to particular trophic states. We demonstrated that trophic type determined the occurrence of certain cyanobacteria species. From among 78 identified taxa, shade- and turbid mixed adapted were the most numerous. Eutrophic ponds had the highest cyanobacteria species and diversity and abundance of zooplankon. Dominating species such as Chroococcus minimus, Anagnostidinema amphibium, Phormidium granulatum or Komvophoron minutum preferred mesotrophic, while e.g. Jaaginema subtilissimum, Limnolyngbya circumcreta, Limnothrix vacuolifera or Romeria leopolienis eutrophic waters and these were not grazed by filtrators. Only 3 species (Aphanizomenon flos-aquae, Dolichospermum circinale, Planktothrix agardhii) were associated with hypertrophic ponds. Therefore, we assume that cyanobacteria taxa have a high indicative potential to distinguish between trophic type of ponds. Reynolds Functional Groups also exhibit responses to changes in water quality. It was partucularly evident in the case of cyanobacteria representatives of codon M which was attributed to eutrophic ponds. Advancing our understanding about trophic preferences of cyanobacteria is crucial, especially in the era of global warming and the persistent issue of water eutrophication, when problems with harmful cyanobacterial blooms are intensifying. The research findings have ecological significance and management implications, highlighting the often-overlooked importance of pond ecosystems in maintaining overall water quality., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Vertical migration behaviour, which is integral to marine energy circulation, is a prevalent trait among marine organisms. However, the behaviour of phytoplankton, particularly beyond diel vertical migration (DVM), remain underexplored compared to groups like zooplankton. Through the lens of the harmful alga Heterosigma akashiwo, which exhibits active vertical migrations and unique fluctuating bloom dynamics, this study aimed to explore the ecological intricacies and diverse benefits of phytoplankton vertical migration behaviours. During the bloom period of H. akashiwo, we unexpectedly observed a dense concentration of cells at bottom layer during daytime. This phase coincided with the emergence of cells related to this species' sexual reproduction. Laboratory experiments further showed an elevated frequency of sexual reproduction in the cell populations that migrated to deeper depths compared to those at the surface. This finding implies a connection between dense bottom accumulation (BA) and the life cycle transitions of the species. This BA phase persisted for two days, after which the populations returned to their standard DVM behaviour, providing insight into the unique fluctuating bloom dynamics of H. akashiwo. Our study suggests that phytoplankton vertical migrations are not strictly dictated by DVM, revealing diverse vertical migration behaviours that may contribute to the complexity of harmful algal bloom patterns., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Our oceans are populated with a wide diversity of planktonic organisms that form complex dynamic communities at the base of marine trophic networks. Within such communities are phytoplankton, unicellular photosynthetic taxa that provide an estimated half of global primary production and support biogeochemical cycles, along with other essential ecosystem services. One of the major challenges for microbial ecologists has been to try to make sense of this complexity. While phytoplankton distributions can be well explained by abiotic factors such as temperature and nutrient availability, there is increasing evidence that their ecological roles are tightly linked to their metabolic interactions with other plankton members through complex mechanisms (e.g. competition and symbiosis). Therefore, unravelling phytoplankton metabolic interactions is the key for inferring their dependency on, or antagonism with, other taxa and better integrating them into the context of carbon and nutrient fluxes in marine trophic networks. In this review, we attempt to summarize the current knowledge brought by ecophysiology, organismal imaging, in silico predictions and co-occurrence networks using 'omics data, highlighting successful combinations of approaches that may be helpful for future investigations of phytoplankton metabolic interactions within their complex communities.This article is part of the theme issue 'Connected interactions: enriching food web research by spatial and social interactions'.

Marine plankton communities form intricate networks of interacting organisms at the base of the food chain, and play a central role in regulating ocean biogeochemical cycles and climate. However, predicting plankton community shifts in response to climate change remains challenging. While species distribution models are valuable tools for predicting changes in species biogeography under climate change scenarios, they generally overlook the key role of biotic interactions, which can significantly shape ecological processes and ecosystem responses. Here, we introduce a novel statistical framework, association distribution modelling (ADM), designed to model and predict ecological associations distribution in space and time. Applied on a Tara Oceans genome-resolved metagenomics dataset, the present-day biogeography of ADM-inferred marine plankton associations revealed four major biogeographic biomes organized along a latitudinal gradient. We predicted the evolution of these biome-specific communities in response to a climate change scenario, highlighting differential responses to environmental change. Finally, we explored the functional potential of impacted plankton communities, focusing on carbon fixation, outlining the predicted evolution of its geographical distribution and implications for ecosystem function.This article is part of the theme issue 'Connected interactions: enriching food web research by spatial and social interactions'.