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Daya Bay, a semi-enclosed bay in the northern South China Sea and to the east of the Pearl River Estuary, is rich in biological resources and diverse habitats. Current research on mesozooplankton in Daya Bay has mainly focused on aspects such as species composition, biomass, and biodiversity in the zooplankton community. However, there is limited research on the top-down effects of mesozooplankton on prey communities. This study conducted seasonal in-situ cultivation experiments from 2015 to 2017. By combining mesozooplankton grazing experiments and microzooplankton dilution experiments, the mesozooplankton clearance rate and trophic cascading effect on low trophic levels were calculated. Results showed evident mesozooplankton selective feeding behavior and corresponding trophic cascades with seasonal variations, these being significantly higher in the spring and summer and lower in the autumn and winter. Different sizes of phytoplankton showed significant differences; large-sized phytoplankton received high feeding rates but low trophic cascades by mesozooplankton, while the opposite was true for small-sized phytoplankton. Trophic cascades contribute in three ways: offsetting direct grazing mortality, changing prey community structure via its effects on different phytoplankton sizes, and reducing ciliate grazing impacts at an average of 14.4 ± 7.8%, maintaining around 70% ciliate grazing impacts in nature. The composition of mesozooplankton was the primary reason for explaining feeding preferences, including size selectivity and omnivory. For instance, high cladoceran abundance caused high feeding rates while, on the other hand, high omnivorous copepods abundance caused high trophic cascades on small-sized phytoplankton. General additive model (GAM) analysis revealed that the changes in trophic cascades were highly dependent on temperature, ciliate abundance, mesozooplankton feeding rates on ciliates, and ciliate feeding rates on phytoplankton. The significance of this study lies in its contribution to providing valuable insights into the role of mesozooplankton in the marine food web and their impact on lower trophic levels. In addition, the findings can help inform the management and conservation of marine ecosystems, as well as guide future research in this field. [ABSTRACT FROM AUTHOR]

The response of mesozooplankton is critical in assessing the health of an estuarine ecosystem. Reports on the spatial and temporal dynamics of mesozooplankton community in estuarine and backwaters of the Southern parts of India are scanty. In this scenario, we appraised the community structure of mesozooplankton and their spatio-temporal dynamics based on various multivariate statistical assessments. A total of 31 taxa were identified and the abundance was principally dominated by Copepoda followed by Luciferidae during three sampling seasons. The most abundant species were: Paracalanus parvus parvus, Pseudodiaptomus aurivillii, Temora stylifera, and Pseudodiaptomus serricaudatus. Canonical correspondence analysis and Spearman's correlation coefficients underlined that salinity, turbidity, conductivity, temperature, dissolved oxygen, chlorophyll a (Chl-a), and nutrients were the principal environmental variables strongly linked with mesozooplankton dynamics in Munroe Island. The highest abundance of mesozooplankton was recorded in MoN (monsoon), followed by PrM (pre-monsoon), and PoM (post-monsoon). Hierarchical clustering confirmed that the grouping of sampling stations is based on the estuarine and freshwater influences on mesozooplankton abundance. During the entire investigation, various ecological indices were observed in good condition. Moreover, the optimum environmental conditions during the PoM season are marked with the highest indices values. Overall, multivariate investigations undoubtedly proved the suitability of mesozooplankton communities as potential bioindicators for spatial and seasonal ecological assessments. Our investigation emphasizes the high assemblages of mesozooplankton and their responses to various environmental variables and highlights the significance of long-term ecological monitoring in a threatened ecosystem like Munroe Island. [ABSTRACT FROM AUTHOR]

Introduction: In the Southern Ocean, the large-scale distribution of zooplankton, including their abundance and community composition from the epipelagic to the upper bathypelagic layers, remains poorly understood. This gap in knowledge limits our comprehension of their ecological and biogeochemical roles. Methods: To better understand their community structure, depth-stratified zooplankton samples were collected from 0 to 1500 m during four summers in the East-Pacific and Indian sectors of the Southern Ocean. In addition, analysis of environmental drivers including temperature, salinity, dissolved oxygen, and chlorophyll a concentration, as well as water masses was conducted. Results: Our study indicates that zooplankton diversity may be similar between the two sectors, while zooplankton abundance was higher in the East-Pacific sector during different sampling months and years. Moreover, zooplankton abundance decreased with depth in both sectors. Based on cluster analysis, zooplankton communities were generally divided by either the epipelagic or the deeper layers' communities. In both sectors, the epipelagic layer was dominated by cyclopoid copepods, such as Oithona similis and Oncaea curvata, as well as calanoid copepods including Calanoides acutus, Rhincalanus gigas, and Ctenocalanus citer, while copepods and other taxa including Chaetognatha, Amphipoda, and Ostracoda, were important contributors to the deep layer communities. Discussion: Our analysis revealed that water masses, combined with their physical characteristics such as specific temperature and salinity ranges and depth, along with biological factors such as chlorophyll a concentration, might be the most important drivers for structuring zooplankton communities from epipelagic to upper bathypelagic layer. [ABSTRACT FROM AUTHOR]

ABSTRACT Aim Location Taxon Methods Results Main Conclusions We aimed to enhance our understanding of the distribution of mesopelagic mesozooplankton (MM) using species distribution models, assess the performance of various modelling techniques, identify key environmental predictors for MM distribution and compute their habitat suitability indices.Our study focused on the mesopelagic zone globally, with data analysed from different oceans.Our focus was primarily on mesopelagic mesozooplankton, gathering data on 861 different species from the Mesopelagic Mesozooplankton and Micronekton (MMM) Database.We used an ensemble of species distribution models, applying 10 different modelling algorithms and three multi‐model ensemble approaches. We explored two important factors that can affect model performance: subsampling and the choice of background points. We also estimated the relative importance of various environmental conditions such as mixed layer depth, temperature, salinity, net primary productivity, euphotic zone depth and dissolved nitrate concentration on the distribution of these species.Euphotic zone depth, salinity and dissolved nitrate concentration were identified as the most important variables for explaining the distribution of mesopelagic mesozooplankton. The ensemble modelling results were robust in areas with abundant observational records, but high uncertainty was observed in data‐limited regions. We found a patchy habitat suitability map for zooplankton when modelled within their native range, largely due to uneven sampling. Unrestricted range models yielded smoother patterns but could inaccurately project species in areas where they do not occur.Our study highlights the need for increased sampling effort in data‐limited regions to improve the accuracy of mesopelagic species distribution models. Despite some inaccuracies, unrestricted range models, assuming ecological equivalence (where different species occupying a similar ecological niche in different geographical regions or different ecosystems exhibit similar adaptations and behaviours), provide a reasonable comparison for habitat suitability maps and model performance. It also confirms the significant impact of certain environmental conditions on mesozooplankton distribution. [ABSTRACT FROM AUTHOR]

We conducted this study to investigate the relationship between environmental stressors and mesozooplankton fluxes in inner Kongsfjorden, Svalbard. The ongoing Arctic amplification, characterized by phenomena such as increased temperatures, glacial and watershed runoff, and diminishing ice cover, poses significant challenges to marine ecosystems. Our multi-year time-series analysis (2010–2018) of mesozooplankton, collected from a moored automatic sediment trap at approximately 87 m depth, aims to elucidate seasonal and interannual variations in fluxes within this Arctic fjord. We integrate meteorological, hydrological, and chemical datasets to assess their influence on zooplankton populations. Principal component analysis reveals the impact of seawater characteristics on mesozooplankton fluxes and composition, while two-way ANOVA highlights the role of seasonality in driving variations in our dataset. We observe a decrease in swimmer fluxes following the maxima mass flux event (from 2013 onwards), coupled with an increase in community diversity, possibly attributed to copepod decline and functional diversity. Notably, sub-Arctic boreal species such as Limacina retroversa have been detected in the sediment trap since 2016. Our continuous multi-year dataset captures the physical, chemical, and biological dynamics in this extreme environment. With Arctic amplification in Kongsfjorden and increasing submarine and watershed runoff, we anticipate significant shifts in mesozooplankton communities in the medium to long-term. This underscores the urgency for further research on their adaptation to changing environmental conditions and the potential introduction of alien species. [ABSTRACT FROM AUTHOR]

Copepods are a major component of metazooplankton and important prey for fish and invertebrates such as crabs, shrimps, and flatworms. Certain bloom-forming dinoflagellates can kill copepods, but there is little research on the interactions between copepods and the bloom-forming dinoflagellates Karenia bicuneiformis and K. selliformis. In this study, the survival and ingestion rates of the calanoid copepod Acartia hongi feeding on K. bicuneiformis and K. selliformis were determined as a function of prey concentration. On day 2, the survival of A. hongi incubated with K. bicuneiformis was 90–100% at all the tested prey concentrations, while that with K. selliformis was 0–20% at ≥ 582 ng C mL−1. Compared to other harmful dinoflagellates from the literature, K. bicuneiformis caused low mortality of Acartia; however, K. selliformis caused almost the highest mortality at similar dinoflagellate concentrations. With increasing mean prey concentration, the ingestion rates of A. hongi feeding on K. bicuneiformis increased on day 1, but those on K. selliformis did not increase. Acartia hongi stopped feeding on K. bicuneiformis at mean prey concentrations of ≥ 341 ng C mL−1 and K. selliformis at all prey concentrations on day 2. At the prey concentration of 1000 ng C mL−1, the ingestion rate of A. hongi feeding on K. bicuneiformis was moderate among the rates of Acartia spp. feeding on harmful dinoflagellates; however, that on K. selliformis was the lowest. These results indicate that K. bicuneiformis and K. selliformis differentially affect the survival and ingestion rates of A. hongi. [ABSTRACT FROM AUTHOR]

Several species from various zooplankton taxa perform seasonal vertical migrations (SVM) of typically several hundred meters between the surface layer and overwintering depths, particularly in high-latitude regions. We use OPtimality-based PLAnkton (OPPLA) ecosystem model) to simulate SVM behavior in zooplankton in the Labrador Sea. Zooplankton in OPPLA is a generic functional group without life cycle, which facilitates analyzing SVM evolutionary stability and interactions between SVM and the plankton ecosystem. A sensitivity analysis of SVM-related parameters reveals that SVM can amplify the seasonal variations of phytoplankton and zooplankton and enhance the reduction of summer surface nutrient concentrations. SVM is often explained as a strategy to reduce exposure to visual predators during winter. We find that species doing SVM can persist and even dominate the summer-time zooplankton community, even in the presence of Stayers, which have the same traits as the migrators, but do not perform SVM. The advantage of SVM depends strongly on the timing of the seasonal migrations, particularly the day of ascent. The presence of higher (visual) predators tends to suppress the Stayers in our simulations, whereas the SVM strategy can persist in the presence of non-migrating species even without higher predators. [ABSTRACT FROM AUTHOR]

The southern Alboran Sea is a dynamic ecosystem and is highly influenced by Atlantic waters. Unfortunately, despite the importance of the mesozooplankton in this ecosystem, the number of studies on this ecosystem is low. The composition and abundance of mesozooplankton communities were studied during the summer season (July 2017) along the Moroccan Mediterranean coast between M'diq and Saïdia. A total of 14 mesozooplankton groups were identified and were dominated by copepods (48%) and cladocerans (35%). Abundance and biomass spatial distribution distinguished two main regions east and west of Al Hoceima. The same distribution pattern was observed when using copepod and cladoceran abundance. Environmental parameters (temperature, salinity, and nutrients) differed in these two regions. Our results confirm the hypothesis that the water flux from the Atlantic Ocean is responsible for the eastward gradients of the mesozooplankton abundance and diversity. Copepods were the most diversified group with 27 species, dominated by Paracalanus parvus (30.5%), Temora stylifera (14%), and Oncaea venusta (12.4%). The diversity index (H') of copepods varied between 1.35 and 2.8 bits ind−1, and the regularity index (J) varied between 0.21 and 0.45, without a remarkable longitudinal gradient. Multivariate analysis showed that the mesozooplankton biomass, abundance, and distribution were influenced mainly by hydrology (gyres), by temperature and salinity, and to a lesser degree by phytoplankton. [ABSTRACT FROM AUTHOR]

From 2010 to 2022, the summed concentrations of six indicator polychlorinated biphenyls (∑6PCB) and DDT with metabolites DDE and DDD (∑DDT) in the surface layer of the coastal Black Sea areas of Crimea varied from 0.05 to 34.9 and from 0.01 to 7.44 ng/L, respectively. The maximum concentrations of both groups of compounds were found during spring seasons. With the total variability in the ∑DDT content in water being significant, their average concentration tended to decrease in the study period. For PCBs, this trend was not detected. The ∑DDT concentration in mesozooplankton in the studied water areas in 2016, 2017, and 2019 reached 34.3; ∑6PCB, 475 ng/g dry weight. A positive correlation between the ∑DDT concentration in mesozooplankton and water samples (R 2 = 0.77) and the lack of such correlation for ∑PCB (R 2 = 0.03) was revealed. It was determined that the accumulation of ∑PCB and ∑DDT in mesozooplankton was directly correlated with the total lipid content in organisms. In the surface layer of sediments in open areas of the Black Sea water area of Crimea, the content of PCB congeners 101, 138, 153, and 180 was the same in 2016 and 2019, which indicates stabilization of the technogenic load on the studied water areas. [ABSTRACT FROM AUTHOR]

Daya Bay, a semi-enclosed bay in the northern South China Sea and to the east of the Pearl River Estuary, is rich in biological resources and diverse habitats. Current research on mesozooplankton in Daya Bay has mainly focused on aspects such as species composition, biomass, and biodiversity in the zooplankton community. However, there is limited research on the top-down effects of mesozooplankton on prey communities. This study conducted seasonal in-situ cultivation experiments from 2015 to 2017. By combining mesozooplankton grazing experiments and microzooplankton dilution experiments, the mesozooplankton clearance rate and trophic cascading effect on low trophic levels were calculated. Results showed evident mesozooplankton selective feeding behavior and corresponding trophic cascades with seasonal variations, these being significantly higher in the spring and summer and lower in the autumn and winter. Different sizes of phytoplankton showed significant differences; large-sized phytoplankton received high feeding rates but low trophic cascades by mesozooplankton, while the opposite was true for small-sized phytoplankton. Trophic cascades contribute in three ways: offsetting direct grazing mortality, changing prey community structure via its effects on different phytoplankton sizes, and reducing ciliate grazing impacts at an average of 14.4 ± 7.8%, maintaining around 70% ciliate grazing impacts in nature. The composition of mesozooplankton was the primary reason for explaining feeding preferences, including size selectivity and omnivory. For instance, high cladoceran abundance caused high feeding rates while, on the other hand, high omnivorous copepods abundance caused high trophic cascades on small-sized phytoplankton. General additive model (GAM) analysis revealed that the changes in trophic cascades were highly dependent on temperature, ciliate abundance, mesozooplankton feeding rates on ciliates, and ciliate feeding rates on phytoplankton. The significance of this study lies in its contribution to providing valuable insights into the role of mesozooplankton in the marine food web and their impact on lower trophic levels. In addition, the findings can help inform the management and conservation of marine ecosystems, as well as guide future research in this field.

The Tsushima Strait and the neighboring waters has been known as major spawning and nursery grounds for migratory fishes due to the high standing stocks of the plankton community in spring to summer. In the present study, spatial and temporal variations in taxonomic composition, standing stocks and productivity of the mesozooplankton community were investigated in the southwestern Japan Sea to explore their variations during the productive seasons. Both spatial and temporal fluctuations were significant for mesozooplankton standing stocks while only temporal variability affected their productivity. The mesozooplankton community was split into one coastal group, represented by cladocerans and noctilucids throughout the seasons, and five pelagic groups, predominated by calanoids, cyclopoids and copepod nauplii, with temporal replacement during spring to summer. The coastal community group contained the additional standing stocks of cladocerans and noctilucids along with the predominant copepods from the other groups and thus resulted in the spatial difference in mesozooplankton standing stocks between coastal and pelagic sites. Three pelagic community groups were characterized by the abundant appearance of noctilucids and clustered toward the pelagic stations neighboring the coastal community group. Generalized linear models demonstrated that salinity was a significant explanatory variable for standing stocks of mesozooplankton and coastal taxonomic groups (i.e., cladocerans and noctilucids). These findings suggest that the spatial and temporal variations in mesozooplankton standing stocks are a mixture of the pelagic community groups with the coastal community group advected toward the pelagic sites. [ABSTRACT FROM AUTHOR]

From 2010 to 2022, the summed concentrations of six indicator polychlorinated biphenyls (∑6PCB) and DDT with metabolites DDE and DDD (∑DDT) in the surface layer of the coastal Black Sea areas of Crimea varied from 0.05 to 34.9 and from 0.01 to 7.44 ng/L, respectively. The maximum concentrations of both groups of compounds were found during spring seasons. With the total variability in the ∑DDT content in water being significant, their average concentration tended to decrease in the study period. For PCBs, this trend was not detected. The ∑DDT concentration in mesozooplankton in the studied water areas in 2016, 2017, and 2019 reached 34.3; ∑6PCB, 475 ng/g dry weight. A positive correlation between the ∑DDT concentration in mesozooplankton and water samples (R 2 = 0.77) and the lack of such correlation for ∑PCB (R 2 = 0.03) was revealed. It was determined that the accumulation of ∑PCB and ∑DDT in mesozooplankton was directly correlated with the total lipid content in organisms. In the surface layer of sediments in open areas of the Black Sea water area of Crimea, the content of PCB congeners 101, 138, 153, and 180 was the same in 2016 and 2019, which indicates stabilization of the technogenic load on the studied water areas. [ABSTRACT FROM AUTHOR]

Abstract—The article discusses the composition and spatial distribution patterns of mesozooplankton communities in the waters of the Bransfield Strait, Antarctic Sound, Powell Basin of the Weddell Sea, and off the Antarctic Peninsula and South Orkney Islands during the austral summer of 2022. Among the mesozooplankton communities, two groups were revealed to be the most abundant: copepods Calanoides acutus, Metridia gerlachei and Oithona spp., and euphausiids Euphausia superba. The maximum abundance and biomass of mesozooplankton were found in warm Antarctic surface water (AASW) off the South Orkney Islands. Correspondingly, the minimum values were found in cold modified Transitional Weddell Sea Water (TWW) off the Antarctic Peninsula. Copepods was concentrated in the Bransfield Strait near the South Shetland Islands with a sea surface temperature (SST) of –0.5 to 0.5°С and sea surface salinity (SSS) of 34.5–34.6‰; krill E. superba eggs and larvae at different stages of development was concentrated in waters off the South Orkney Islands with SST values of 1–2°С and SSS values of 34.3–34.5‰. Four groups of mesozooplankton communities with different composition, abundance, and taxonomic dominance were identified. The results of this and future studies have practical implications for monitoring the state of the changing ecosystem of the Southern Ocean. [ABSTRACT FROM AUTHOR]

The southern Alboran Sea is a dynamic ecosystem and is highly influenced by Atlantic waters. Unfortunately, despite the importance of the mesozooplankton in this ecosystem, the number of studies on this ecosystem is low. The composition and abundance of mesozooplankton communities were studied during the summer season (July 2017) along the Moroccan Mediterranean coast between M’diq and Saïdia. A total of 14 mesozooplankton groups were identified and were dominated by copepods (48%) and cladocerans (35%). Abundance and biomass spatial distribution distinguished two main regions east and west of Al Hoceima. The same distribution pattern was observed when using copepod and cladoceran abundance. Environmental parameters (temperature, salinity, and nutrients) differed in these two regions. Our results confirm the hypothesis that the water flux from the Atlantic Ocean is responsible for the eastward gradients of the mesozooplankton abundance and diversity. Copepods were the most diversified group with 27 species, dominated by Paracalanus parvus (30.5%), Temora stylifera (14%), and Oncaea venusta (12.4%). The diversity index (H’) of copepods varied between 1.35 and 2.8 bits ind−1, and the regularity index (J) varied between 0.21 and 0.45, without a remarkable longitudinal gradient. Multivariate analysis showed that the mesozooplankton biomass, abundance, and distribution were influenced mainly by hydrology (gyres), by temperature and salinity, and to a lesser degree by phytoplankton.

The northern Andaman Sea off Myanmar is one of the relatively high productive regions in the Indian Ocean. The abundance, biomass and species composition of mesozooplankton and their relationships with environmental variables in the epipelagic zone (∼200 m) were studied for the first time during the Sino-Myanmar joint cruise (February 2020). The mean abundance and biomass of mesozooplankton were (1 916.7±1 192.9) ind./m3 and (17.8±7.9) mg/m3, respectively. A total of 213 species (taxa) were identified from all samples. The omnivorous Cyclopoida Oncaea venusta and Oithona spp. were the top two dominant taxa. Three mesozooplankton communities were determined via cluster analysis: the open ocean in the Andaman Sea and the Bay of Bengal (Group A), the transition zone across the Preparis Channel (Group B), and nearshore water off the Ayeyarwady Delta and along the Tanintharyi Coast (Group C). Variation partitioning analysis revealed that the interaction of physical and biological factors explained 98.8% of mesozooplankton community spatial variation, and redundancy analysis revealed that column mean chlorophyll a concentration (CMCHLA) was the most important explanatory variable (43.1%). The abundance and biomass were significantly higher in Group C, the same as CMCHLA and column mean temperature (CMT) and in contrast to salinity, and CMT was the dominant factor. Significant taxon spatial variations were controlled by CMCHLA, salinity and temperature. This study suggested that mesozooplankton spatial variation was mainly regulated by physical processes through their effects on CMCHLA. The physical processes were simultaneously affected by heat loss differences, freshwater influx, eddies and depth. [ABSTRACT FROM AUTHOR]

The Southern Ocean has undergone significant climate-related changes in recent decades. As a result, pelagic communities inhabiting these waters, particularly mesozooplankton, have adapted to new conditions. The present study considers the patterns of horizontal and vertical (up to 1000 m) distribution, the composition, abundance, and biomass of mesozooplankton, and the relationships of these parameters to the extreme environmental conditions off the western Antarctic Peninsula throughout the record-warm austral summer season of 2022. Sampling was conducted using the opening/closing Multinet system (0.25 m2 aperture) equipped with five 150-μm mesh nets and a WP-2 net. The mesozooplankton was represented by the three most abundant groups: eggs and larvae of euphausiids such as Euphausia superba, small copepods such as Oithona similis, and large calanoid copepods such as Calanoides acutus, Calanus propinquus, Metridia gerlachei, and Rhincalanus gigas. The composition and quantitative distribution of the mesozooplankton significantly varied: the copepods were abundant in the west, off the Antarctic Peninsula, while eggs and larvae of euphausiids were abundant in the east, off the South Orkney Islands. Most mesozooplankton occurred in the upper 200 m layer, and each taxon showed characteristic depth preference: small copepods, euphausiids larvae, and cirripeds cypris larvae were abundant in the epipelagic layer, while large calanoid copepods, euphausiids eggs, amphipods, pelagic polychaetes, and ostracods were found mostly in the mesopelagic layer. The composition and quantitative distribution of mesozooplankton had clear relationships with environmental factors, particularly with a combination of variables such as water salinity, temperature, and chlorophyll a concentration. [ABSTRACT FROM AUTHOR]

Pelagic ecosystems are changing in response to the recent climate warming. The mesozooplankton and copepods in particular are important indicators of the state of aquatic ecosystems. Zooplankton in Antarctic waters has been monitored regularly to study biodiversity, food chains, and ecological cycles. In 2021–2022, pilot study of mesozooplankton groups was added to the marine biological research of the Ukrainian Antarctic Program. The preliminary information was obtained on the taxonomic composition and functional characteristics of the taxocene of copepods in the coastal waters of the Argentine Islands. The observed diversity is strongly influenced by the conditions and the available sampling gear. The samples were collected from motor boats using three kinds of plankton nets depending on the weather and ice conditions. From June to February, the predominant species were the common coastal species and species adapted to feeding in the cold upper layers in winter. Trawling samples collected from March to late May best illustrate the seasonal dynamics of the mesozooplankton communities’ temporary and permanent components. Twelve copepods from eight families were identified to the species level. Most constituent species were omnivorous (7 species), followed by detritophages (3 species). The community’s phytophages and predators were locally common. This trophic distribution likely is evidence that they were collected in the surface layer, which is not always favorable for feeding. Therefore, the percentage of omnivorous opportunists was relatively high. Some of the sampled material requires molecular-biological analysis, especially the copepods from the Oncaea Philippi, 1843 and Triconia Böttger-Schnack, 1999 genera. The older copepodites, in particular the adult specimens, were rarely collected. The state of the material was not ideal for unambiguous identification by morphological features. Comparing the results with the latest research on the west coast of the Antarctic Peninsula, we see that the species composition is highly similar (around 80%), except for the deep-water taxa.

Gyrodinium jinhaense and G. moestrupii were described within the past two decades, but the interactions between these two Gyrodinium species and copepods remain to be studied. To elucidate these interactions, the ingestion rate of the calanoid copepods Acartia spp. feeding on G. jinhaense, G. dominans, and G. moestrupii was determined. The maximum ingestion rates of A. hongi/A. omorii on G. jinhaense and G. dominans (3680 and 3480 ng C predator−1d−1, respectively) were similar, but they were considerably higher than that on G. moestrupii (1600 ng C predator−1d−1). The largest size and fastest swimming speed of G. moestrupii may be partially responsible for this lowest maximum ingestion rate. The ingestion rates of A. hongi/A. omorii on G. jinhaense, G. dominans, and G. moestrupii at the prey concentrations of both 50 and 100 ng C mL−1 were higher than those on the heterotrophic dinoflagellates Pfiesteria piscicida and Luciella masanensis but lower than those on the heterotrophic dinoflagellates Stoeckeria algicida and Oxyrrhis marina. Therefore, G. jinhaense, G. dominans, and G. moestrupii are moderate heterotrophic dinoflagellate prey for Acartia spp. [ABSTRACT FROM AUTHOR]

This study is the first to explore monthly and seasonal succession of the zooplankton community in coastal waters of Cyprus using a 12-month period time series. A total of 192 taxa of mesozooplankton (MZ), 145 of which were copepods, were identified at three sites at the southern and one site at the northern coasts of the island. Zooplankton distribution and community structure were influenced mostly by stratification, temperature and Chl-a. The combination of upwelling and advection from the Rhodes Gyre during summer, causing cooler waters in the southern coast of Cyprus, seems to control the food supply and offered favorable feeding conditions to zooplankton, enhancing their numbers. The proximity to a fish farm also positively affected MZ abundance and biomass. This study also revealed the importance of smaller species (e.g. Clausocalanus paululus) and juvenile stages (e.g. Clausocalanus , Oithona and Corycaeus spp.) in composition, structure and functionality of the copepod community. These species seems to be more important in low Chl-a environments, where the relative size of primary consumers is expected to be smaller and the microbial components dominant. This baseline study paves the way for further investigation of the elements of marine food webs in the ultra-oligotrophic environment of the Eastern Mediterranean. [ABSTRACT FROM AUTHOR]

İskenderun Bay is a hotspot for bioinvasions in the Mediterranean Sea, where alien species are frequently introduced, easily settle, and therefore, can often be encountered. The small-sized invasive copepod Oithona davisae (Ferrari and Orsi, 1984) has rapidly spread in several ecosystems worldwide, including the Black Sea, Wadden Sea, Marmara Sea, Adriatic Sea, and Aegean Sea, becoming an integral part of the pelagic communities there. Here, we report O. davisae in İskenderun Bay, in the north-eastern part of the Mediterranean Sea, and provide information on its spatiotemporal variation and assess its potential impact on the seasonal abundance and biomass of the mesozooplankton community, at present and in the near future. Zooplankton abundance and biomass were at their lowest levels in winter (1066 ± 313 ind. m-3, 1.9 ± 0.8 mg m-3) and highest in spring (7738 ± 1583 ind. m-3, 18.5 ± 5.8 mg m-3). However, the relative abundance of oithonid copepods was highest during the winter (35.7 ± 10%). The proportion of copepodites in the oithonid assemblage was high in spring (72.5 ± 9.3%), summer (72.7 ± 13.3%) and winter (68.5 ± 3.6%) but the relative abundance of male oithonids remained low across all seasons. Oithona davisae was observed only in the autumn, in abundances of 8.4 to 12.6 ind. m-3. These low abundances could be attributed to the new arrival of this species and the relatively large mesh size used in this study (200 µm). Nevertheless, the successful introduction and assimilation into other mesozooplankton communities elsewhere, rapid adaptability and wide tolerance to environmental conditions of O. davisae, suggest that this species may become a dominant part of the zooplankton community across the Levantine Basin in the very near future. [ABSTRACT FROM AUTHOR]

Samples of mesozooplankton were collected and analysed from two contrasting coastal regions; Muscat (Sea of Oman) and Salalah (Arabian Sea). Copepods represented 41-44% of total biomass. Small species such as Temora turbinata, Oithona spp., Oncaea spp. and Microsetella spp. were abundant but their contribution to total biomass was small compared with the much rarer but larger species such as Eucalanidae, Calanoides natalis or Labidocera pavo. In Muscat, T. turbinata was particularly abundant, whereas C. natalis and Eucalanidae were more abundant in Salalah. Biomass in Muscat seems to be associated with a series of different species peaks showing no clear seasonality. However, biomass in Salalah followed a distinct seasonality with higher biomass during southwest monsoon., a seasonality pattern was observed with the meroplankton/holoplankton ratio in Salalah but not in Muscat. PERMANOVA analysis indicated that the communities structure showed geographic and seasonal differences. The effect of seasonality was particularly visible when the dataset included non-copepods, highlighting the role of this group in structuring mesozooplankton communities. Non-copepods such as chaetognaths and doliolids had a high biomass contribution to both geographic areas. normalized size spectra in both regions were similar and suggested that smaller species were underestimated Whereas, large species, especially chaetognaths, were over-represented. [ABSTRACT FROM AUTHOR]

Some planktonic patches have markedly higher concentrations of organisms compared to ambient conditions and are

To provide a baseline description of copepod assemblages in the Pechora Sea, an estuarine area with great economical and ecological importance, we conducted a survey during the summer season. A total of 24 copepod taxa were identified in the study, with Acartia longiremis, Calanus finmarchicus, Centropages hamatus, Copepoda nauplii, Eurytemora affinis, Oithona similis, Pseudocalanus spp., and Temora longicornis being the most numerous. The high diversity (Shannon index = 2.51 ± 0.06), density (18,720 ± 3376 individuals m−3) and biomass (89 ± 18 mg dry mass m−3) of copepods were revealed. Populations of common small copepod taxa were dominated by the young stages, indicating spawning, while older copepodites prevailed among medium- and large-sized species, showing that their reproduction occurred before our survey. Cluster analysis indicated three groups of stations that mainly differed in the abundance of particular species. There were clear associations between copepod assemblages and environmental variables. Statistical analyses showed significant correlations between copepod abundance and water temperature or sampling depth, while other factors had a lesser influence. Our results suggest a strong effect of local circulation and currents on the spatial pattern of the copepod assemblages in the study area. This study may be useful for future biomonitoring in the south-eastern Barents Sea. [ABSTRACT FROM AUTHOR]

The different characteristics and atmospheric forces over the Sea of Oman and the Arabian Sea are assumed to influence zooplankton seasonality and community structure. This work aimed to characterize the abundances and seasonality of coastal and surface mesozooplankton communities in the Sea of Oman (Muscat) and the Arabian Sea (Salalah), and the effects of environmental factors on their distribution. Zooplankton samples two contrasting coastal regions; 22 in the Sea of Oman, and 20 in the Arabian Sea, were collected during 2013-2014 from the surface and analyzed. Total zooplankton abundance was divided by the number of samples to obtain the monthly average abundance per meter cube (ind•m-3) of sea water. A total of 91 species were observed from all 42 samples of which 58 were copepods, among which 47 were calanoid copepods. Species composition varied significantly between the two locations. The similarity between the two communities was highest (samples were closest to each other) during the winter, and showed the largest differences in composition in the summer. The seasonal changes in community structures were most significant for copepods and calanoid copepods (p= 0.0002 and p= 0.0003 respectively) and less significant for non-copepods (p= 0.0057). Only few species (17 in the Sea of Oman and 20 in the Arabian Sea) represented more than 90% of the total zooplankton abundance. There was a distinct pattern of seasonal variation in the abundance of zooplankton in the Arabian Sea, especially copepods and meroplankton, but there was no such pattern in the Sea of Oman. Some successful species such as Temora turbinata and Penilia avirostris in the Sea of Oman, and Oithona spp. in the Arabian Sea seem able to exploit a wide range of prey from phytoplankton to small ciliates and thus feed through the microbial loop. [ABSTRACT FROM AUTHOR]

It is claimed that oceanic hydrothermal vents (HVs), particularly the shallow water ones, offer particular advantages to better understand the effects of future climate and other global change on oceanic biota. Marine hydrothermal vents (HVs) are extreme oceanic environments that are similar to projected climate changes of the earth system ocean (e.g., changes of circulation patterns, elevated temperature, low pH, increased turbidity, increased bioavailability of toxic compounds. Studies on hydrothermal vent organisms may fill knowledge gaps of environmental and evolutionary adaptations to this extreme oceanic environment. In the present contribution we evaluate whether hydrothermal vents can be used as natural laboratories for a better understanding of zooplankton ecology under a global change scenario. [ABSTRACT FROM AUTHOR]

Bioaccumulation by zooplankton is the outset for persistent organic pollutants that enter the marine food chain. Owing to a full spectrum of anthropogenic activities, the Gaoping waters of southwestern Taiwan are exposed to large quantities of polybrominated diphenyl ethers (PBDEs). However, information on these contaminants in zooplankton in this study area is lacking. In this study, we analyzed 19 PBDE congeners concentrations in 36 zooplankton samples from the Gaoping waters. A high variation in the total PBDE concentrations in zooplankton (from not detected to 1415 ng g−1 dry weight) was found, with the highest PBDE levels being recorded near the entrance of the Kaohsiung Harbor (KH). Significantly higher levels were noted for the KH transect than for the Gaoping River estuary (GR) and Fengshan Township (FS) transects, indicating that PBDE inputs originate from the ocean sewage outfalls. BDE-15 (43%) and BDE-209 (16%) were the predominant PBDE congeners in the zooplankton. Our results suggest that anthropogenic activities might predominantly contribute to significantly high PBDE concentrations. The traditional food web may easily transport these higher levels of PBDEs in zooplankton to higher trophic levels of marine organisms, since the Gaoping waters serve as essential nursery and spawning grounds for invertebrates and fishes. [ABSTRACT FROM AUTHOR]

Global warming is increasing the frequency and severity of the marine heat waves, which poses a serious threat to the marine ecosystem. This study analyzes seasonal and interannual dynamics in the abundance and structure of the mesozooplankton community in Sevastopol Bay based on bi-monthly routine observations over 2003–2014. The focus is on the impact of the summer 2010 marine heat wave (MHW2010) on crustaceans belonging to different ecological groups. As a response to the MHW2010, three warm-water species (O. davisae, A. tonsa and P. avirostris) exhibiting the maximum seasonal density in latter summer showed a sharp increase in the annual abundance and their share in the mesozooplankton community. The increase in the annual abundance in 2010 of the eurythermal species P. parvus and P. polyphemoides exhibiting seasonal peaks in spring and autumn is not related to the MHW2010 but can be explained by a rise of temperature in the first part of the year. O. davisae and A. tonsa showed the most pronounced response among the species to the MHW2010, confirming that non-native species exhibited great flexibility as an adaptive response to environmental changes, especially in the case of climate warming. Among crustaceans observed in this study, O. davisae can be considered as an indicator of the environmental conditions associated with the warming of the Black Sea and the Mediterranean basin as a whole. [ABSTRACT FROM AUTHOR]

A synoptic gulf-wide isoscape of carbon (δ13C) and nitrogen (δ15N) in the Gulf of Mexico based on mesozooplankton (335-1000 um) was used as a proxy for the isotopic baseline and for calculating regional contributions of dissolved inorganic nitrogen sources. Mesozooplankton were sampled at 0-200 m (depth permitting) during the XIXIMI-06 and GOMECC-3 cruises held during the summer of 2017. A striking latitudinal gradient was found in δ15N values of zooplankton, with the highest values (10.4 ± 1.2‰) found over the northern shelf, and lowest values in the central, oligotrophic gulf (1.9 ± 0.5‰). To estimate the fractional contribution of potential nitrogen sources, the gulf was divided into six regions based on the spatial distribution of surface Chl-a, SST from remote sensing products and likely region-specific source contributions. A literature survey of (δ13C and δ15N values of particulate organic matter was used to characterize region-specific endpoint isotope ratios for use in a Bayesian isotope mixing model. Regional differences in δ15N values and the results of mixing models indicated nitrogen fixation is most likely an important source (45-74% contribution) of new nitrogen in the oceanic regions of the Gulf, the Loop Current and the Yucatan Shelf. In the oligotrophic gulf, the potential input of relatively light nitrate that reflects remineralization of surface layer POM or the excretion of light nitrogen by heterotrophs was insufficient to explain the low δ15N values found in the central Gulf, although it could account for about 40% of the N supporting secondary production. The high nitrogen isotope ratios found in the northern shelf were attributed to denitrified N (60%) and the inflow of heavy nitrogen from the Mississippi-Atchafalaya river system. Our results support the potential importance of fixed nitrogen in the deep waters of the Gulf of Mexico during the summer, characteristic for its highly stratified surface waters.

We analyzed seven El Niño events (springs 1958–59, 1983, 1992–93, 1998, 2003, 2010, and 2016) and the 2014–15 Pacific Warm Anomaly (spring 2015) for their impacts on zooplankton biomass and community composition in the southern sector of the California Current System (CCS). Although total mesozooplankton carbon biomass was only modestly affected during El Niño springs, community composition changed substantially. Carbon biomass of five major zooplankton taxa correlated negatively with San Diego sea level anomaly (SDSLA), a regional metric of El Niño physical impacts in the CCS. Additional taxa were negatively related to SDSLA via a time-lagged response reflected in an autoregressive-1 (AR-1) model. All five SDSLA-correlated taxa decreased in carbon biomass during most El Niño years compared to the surrounding years; the exception was the mild event of 2003. Principal Component Analysis revealed coherent species-level responses to El Niño within the euphausiids, copepods, and hyperiid amphipods. Percent similarity index (PSI) comparisons showed pronounced changes in the compositions of euphausiid and, to a lesser extent, calanoid copepod communities during El Niño. By grouping El Niños into Eastern Pacific (EP) versus Central Pacific (CP) events based on their expressions along the equator, we found that CCS zooplankton assemblages showed a tendency toward greater changes in species composition during EP than CP El Niños, although we had low statistical power for these comparisons. Several species showed consistent biomass changes across La Niña events as well, generally opposite in sign to El Niño responses, but overall community composition showed minimal change during La Niña. Carbon biomass and community composition returned to pre-Niño levels within 1–2 years following almost every event, suggesting high resilience of southern CCS zooplankton to El Niño perturbations to date.

We analyzed seven El Niño events (springs 1958–59, 1983, 1992–93, 1998, 2003, 2010, and 2016) and the 2014–15 Pacific Warm Anomaly (spring 2015) for their impacts on zooplankton biomass and community composition in the southern sector of the California Current System (CCS). Although total mesozooplankton carbon biomass was only modestly affected during El Niño springs, community composition changed substantially. Carbon biomass of five major zooplankton taxa correlated negatively with San Diego sea level anomaly (SDSLA), a regional metric of El Niño physical impacts in the CCS. Additional taxa were negatively related to SDSLA via a time-lagged response reflected in an autoregressive-1 (AR-1) model. All five SDSLA-correlated taxa decreased in carbon biomass during most El Niño years compared to the surrounding years; the exception was the mild event of 2003. Principal Component Analysis revealed coherent species-level responses to El Niño within the euphausiids, copepods, and hyperiid amphipods. Percent similarity index (PSI) comparisons showed pronounced changes in the compositions of euphausiid and, to a lesser extent, calanoid copepod communities during El Niño. By grouping El Niños into Eastern Pacific (EP) versus Central Pacific (CP) events based on their expressions along the equator, we found that CCS zooplankton assemblages showed a tendency toward greater changes in species composition during EP than CP El Niños, although we had low statistical power for these comparisons. Several species showed consistent biomass changes across La Niña events as well, generally opposite in sign to El Niño responses, but overall community composition showed minimal change during La Niña. Carbon biomass and community composition returned to pre-Niño levels within 1–2 years following almost every event, suggesting high resilience of southern CCS zooplankton to El Niño perturbations to date.

The principal objectives of this research are to measure the non-consumptive mortality rate of marine copepod zooplankton and the sedimentation rate of copepod carcasses, using short-term sediment traps, and to reveal a correlation between the rates of the two competitive processes—sedimentation and degradation of the carcasses under turbulent mixing conditions. The traps were moored in Sevastopol Bay and adjacent coastal waters (the Black Sea) during summer and autumn seasons. A simulation model was developed to describe a wide range of processes in the trap and the water column above it and to interpret the results obtained with the sediment traps. Significant changes in the abundance of copepod carcasses (from 280 to 12,443 ind. m−3) and their fraction in the total zooplankton abundance (53 to 81%) were observed in the waters over short time periods, indicating a high variability of zooplankton mortality, sedimentation, and decomposition rates. Despite the high concentrations of copepod carcasses in the water column, the rates of their accumulation in the traps proved to be extremely low, which could be due to intense turbulent mixing of the waters. The carcass sedimentation rate and the flow of swimmers (motile copepods) into the traps were significantly higher in waters subjected to weaker turbulent mixing. The obtained estimates of the sedimentation rate of copepod carcasses (0.012 to 0.39 d−1) were comparable in value with the rate of their microbial decomposition (0.13 and 0.05 d−1 in the bay and adjacent waters, respectively). This confirmed the hypothesis on microbial decomposition as one of the key controls of the fraction of live zooplankton organisms in zooplankton. [ABSTRACT FROM AUTHOR]

Zooplankton plays a crucial role in marine ecosystems. However, due to issues with morphological identification and sampling methods, knowledge of their biodiversity and community structure in the vast pelagic zone of the western tropical Pacific Ocean is still limited compared with other areas in the North Pacific Ocean. In this study, we used environmental DNA (eDNA) metabarcoding and morphological identification approaches to investigate mesozooplankton’s biodiversity and vertical assemblages in the western tropical Pacific Ocean from the surface to 1000 m deep. Two different barcodes were used in metabarcoding: mitochondrial cytochrome oxidase I (COI) and small subunit ribosomal RNA genes (18S). Our results showed that eDNA metabarcoding revealed 2-4 times more medusae taxa than morphological processing. Both methods detected that small copepod species were dominant in the community and six of the top-10 most abundant copepod genera overlapped. Morphological results showed that mesozooplankton communities were classified into three groups: epipelagic (0–200 m), upper mesopelagic (200-500 m), and lower mesopelagic (500–1000 m). And eDNA results showed distinct vertical variations of mesozooplankton communities within the epipelagic. Both methods showed that the dominant genera Clausocalanus, Paracalanus, and Calocalanus exhibited diel patterns in relative abundance, demonstrating that the eDNA method can capture diel vertical migration (DVM) signals of copepods. Overall, our results indicate that eDNA metabarcoding is an effective and efficient tool for the study and monitoring of mesozooplankton diversity and vertical assemblages in the open sea.

The Southern Ocean has undergone significant climate-related changes in recent decades. As a result, pelagic communities inhabiting these waters, particularly mesozooplankton, have adapted to new conditions. The present study considers the patterns of horizontal and vertical (up to 1000 m) distribution, the composition, abundance, and biomass of mesozooplankton, and the relationships of these parameters to the extreme environmental conditions off the western Antarctic Peninsula throughout the record-warm austral summer season of 2022. Sampling was conducted using the opening/closing Multinet system (0.25 m2 aperture) equipped with five 150-μm mesh nets and a WP-2 net. The mesozooplankton was represented by the three most abundant groups: eggs and larvae of euphausiids such as Euphausia superba, small copepods such as Oithona similis, and large calanoid copepods such as Calanoides acutus, Calanus propinquus, Metridia gerlachei, and Rhincalanus gigas. The composition and quantitative distribution of the mesozooplankton significantly varied: the copepods were abundant in the west, off the Antarctic Peninsula, while eggs and larvae of euphausiids were abundant in the east, off the South Orkney Islands. Most mesozooplankton occurred in the upper 200 m layer, and each taxon showed characteristic depth preference: small copepods, euphausiids larvae, and cirripeds cypris larvae were abundant in the epipelagic layer, while large calanoid copepods, euphausiids eggs, amphipods, pelagic polychaetes, and ostracods were found mostly in the mesopelagic layer. The composition and quantitative distribution of mesozooplankton had clear relationships with environmental factors, particularly with a combination of variables such as water salinity, temperature, and chlorophyll a concentration.

Zooplankton play a pivotal role in connecting primary producers and high trophic levels, and changes in their temporal and spatial distribution may affect the entire marine ecosystem. The spatial and seasonal taxonomic composition patterns of mesozooplankton in Bohai Bay were investigated in relation to a number of water parameters. Bohai Bay is a eutrophic semi-enclosed bay with dynamic physico-chemical conditions influenced by terrestrial inputs and seawater intrusion. The results showed that under the condition of terrigenous input, the diversity of mesozooplankton species near the eutrophic Haihe River Estuary and Jiyun River Estuary was lower than that in the central Bohai Bay, with gelatinous Oikopleura dioica as the dominant species. The mesozooplankton diversity was highest in the bay mouth affected by seawater intrusion, and the dominant oceanic species, mainly copepods Corycaeus affinis, Calanus sinicus, and Oithona similis, entered the inner bay from the bay mouth. Meanwhile, the abundance of mesozooplankton in summer was significantly higher than that in autumn. Compared with historical data, the dominant species in Bohai Bay has evolved from arrow worm Sagitta crassa to copepod Paracalanus parvus, probably due to global warming, indicating the effects of human activities on the succession of mesozooplankton community. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Mesozooplankton Diversity: Thirty-five species/taxa recorded, with copepods dominating in abundance. • Copepod Functional Groups: Three functional groups identified, showing spatial preferences and feeding strategies. • Significant Taxonomic Differences: Mesozooplankton assemblage vary between zones within each estuary and among them. • Significant Functional Groups Differences: Copepod functional groups vary between zones and within saline estuary inner zones. • Environmental Drivers of Mesozooplankton: Salinity shapes mesozooplankton taxonomic structure and copepod functional groups. [ABSTRACT FROM AUTHOR]

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. • Estimate the respiration and growth of zooplankton across a trophic gradient in Saronikos Gulf using biochemical indices. • ETS, AaRs are correlated with both biological and environmental data providing new insights of the role of mesozooplankton. • Determine seasonal zooplankton carbon demands by integrating data on zooplankton biomass and metabolic estimates. [ABSTRACT FROM AUTHOR]

İskenderun Bay is a hotspot for bioinvasions in the Mediterranean Sea, where alien species are frequently introduced, easily settle, and therefore, can often be encountered. The small-sized invasive copepod Oithona davisae (Ferrari and Orsi, 1984) has rapidly spread in several ecosystems worldwide, including the Black Sea, Wadden Sea, Marmara Sea, Adriatic Sea, and Aegean Sea, becoming an integral part of the pelagic communities there. Here, we report O. davisae in İskenderun Bay, in the north-eastern part of the Mediterranean Sea, and provide information on its spatiotemporal variation and assess its potential impact on the seasonal abundance and biomass of the mesozooplankton community, at present and in the near future. Zooplankton abundance and biomass were at their lowest levels in winter (1066 ± 313 ind. m-3, 1.9 ± 0.8 mg m-3) and highest in spring (7738 ± 1583 ind. m-3, 18.5 ± 5.8 mg m-3). However, the relative abundance of oithonid copepods was highest during the winter (35.7 ± 10%). The proportion of copepodites in the oithonid assemblage was high in spring (72.5 ± 9.3%), summer (72.7 ± 13.3%) and winter (68.5 ± 3.6%) but the relative abundance of male oithonids remained low across all seasons. Oithona davisae was observed only in the autumn, in abundances of 8.4 to 12.6 ind. m-3. These low abundances could be attributed to the new arrival of this species and the relatively large mesh size used in this study (200 μm). Nevertheless, the successful introduction and assimilation into other mesozooplankton communities elsewhere, rapid adaptability and wide tolerance to environmental conditions of O. davisae, suggest that this species may become a dominant part of the zooplankton community across the Levantine Basin in the very near future. [ABSTRACT FROM AUTHOR]

This study presents how human-altered hydrographical settings (flow restrictions) impacts the natural distribution and community structure of copepods in the Kochi Backwaters (KBW), the largest monsoonal estuary along the southwest coast of India. This study is primarily based on an extensive seasonal sampling in the KBW and their comparison with a historical data set. Thannermukkom Barrage (TB) was built in the southern section of the KBW in the 1970s to prevent saline water intrusion to the upstream during the non-monsoon periods. Thirteen locations (1–4 in the downstream, 5–9 in the midstream, and 10–13 in the upstream) were sampled in this study over the entire stretch of the KBW during the Pre-Southwest Monsoon (PRM), Southwest Monsoon (SWM), and Post-Southwest Monsoon (PSWM). The overall effect of TB in the KBW is a seaward push of mesohaline conditions during all seasons with varying intensities. In response to the seaward push of mesohaline conditions, copepods Acartiella keralensis, Acartia plumosa, Acartia sp., Pseudodiaptomus annandalei, Pseudodiaptomus serricaudatus, Euterpina acutifrons and Oithona brevicornis showed a corresponding spatial shift for their highest abundance and diversity from midstream during PRM to the downstream during the SWM/PSWM. Multivariate and IndVal analysis demarcated many indicator species of copepods of different hydrographical settings in the KBW. A comparison with the historical data set showed that there is an apparent long-term change in hydrography, copepod composition and community structure in the upstream of the KBW due to TB.

Reducing nutrient loads from catchments is an important strategy to mitigate coastal eutrophication. The decadal responses of ecosystems to nutrient load reductions can help us understand the effectiveness of environmental restoration. Here, the cascading trophic interactions of mesozooplankton and phytoplankton in Laizhou Bay were analyzed to examine the effects of nutrient load reductions from rivers during 2004–2014. The results showed that the diversity of the mesozooplankton assemblages and the proportion of higher trophic species increased after nutrient load reductions, and mesozooplankton abundance showed an obviously decreasing annual trend. A significantly positive correlation between mesozooplankton and phytoplankton abundance was identified for August. Mesozooplankton abundance was mainly influenced by phytoplankton abundance in August, but by microzooplankton prey or jellyfish predators in May when phytoplankton abundance was low. This result indicates that the recovery of mesozooplankton assemblages in Laizhou Bay is a slow process after nutrient load reductions and might have cascading trophic interactions with phytoplankton recovery.

The spatio-temporal distributions of the epipelagic mesozooplankton community in the western Ross Sea region marine protected area (RSR MPA) were investigated. Mesozooplankton surveys were conducted in February 2018, January 2019, and March 2020 from an approximate depth of 200 m to address the essential environmental factors influencing the mesozooplankton community structure. Our results showed that the mesozooplankton community of the western RSR MPA could be affected by the various ecological factors, depending on their temporal and spatial variations. The community structure in 2018 was distinguished by its chlorophyll-a (Chl-a) concentration during the summer bloom phase in the late summer. Taxa observed in 2019 were divided into four significantly different groups according to the body size of the community composition. This differentiation could be derived from predation pressure, inducing a trophic cascade. Taxa in the 2020 samples were separated into five different groups based on temperature; during the 2020 survey, the water temperature was low and sea ice covered the whole continental shelf in the Ross Sea. Additionally, comparing the results from the three interannual surveys, although the communities clustered according to the survey period, the continental shelf groups were quite dissimilar despite overlapping geographically. Taken all together, the mesozooplankton community of the western RSR MPA changed according to changes in several ecological factors, such as temperature, Chl-a concentration, and predation pressure. The occurrence of summer blooms and the decline in water temperature mainly regulated the mesozooplankton community structure in the late summer.

Mesozooplankton play a key role in marine ecosystems as they modulate the transfer of energy from phytoplankton to large marine organisms. In addition, they directly influence the oceanic cycles of carbon and nutrients through vertical migrations, fecal pellet production, respiration, and excretion. Mesozooplankton are mainly made up of metazoans, which undergo important size changes during their life cycle, resulting in significant variations in metabolic rates. However, most marine biogeochemical models represent mesozooplankton as protists-like organisms. Here, we study the potential caveats of this simplistic representation by using a chemostat-like zero-dimensional model with four different Nutrient-Phytoplankton-Zooplankton configurations in which the description of mesozooplankton ranges from protist-type organisms to using a size-based formulation including explicit reproduction and ontogenetic growth. We show that the size-based formulation strongly impacts mesozooplankton. First, it generates a delay of a few months in the response to an increase in food availability. Second, the increase in mesozooplankton biomass displays much larger temporal variations, in the form of successive cohorts, because of the dependency of the ingestion rate to body size. However, the size-based formulation does not affect smaller plankton or nutrient concentrations. A proper assessment of these top-down effects would require implementing our size-resolved approach in a 3-dimensional biogeochemical model. Furthermore, the bottom-up effects on higher trophic levels resulting from the significant changes in the temporal dynamics of mesozooplankton could be estimated in an end-to-end model coupling low and high trophic levels. [ABSTRACT FROM AUTHOR]

To provide a baseline description of copepod assemblages in the Pechora Sea, an estuarine area with great economical and ecological importance, we conducted a survey during the summer season. A total of 24 copepod taxa were identified in the study, with Acartia longiremis, Calanus finmarchicus, Centropages hamatus, Copepoda nauplii, Eurytemora affinis, Oithona similis, Pseudocalanus spp., and Temora longicornis being the most numerous. The high diversity (Shannon index = 2.51 ± 0.06), density (18,720 ± 3376 individuals m−3) and biomass (89 ± 18 mg dry mass m−3) of copepods were revealed. Populations of common small copepod taxa were dominated by the young stages, indicating spawning, while older copepodites prevailed among medium- and large-sized species, showing that their reproduction occurred before our survey. Cluster analysis indicated three groups of stations that mainly differed in the abundance of particular species. There were clear associations between copepod assemblages and environmental variables. Statistical analyses showed significant correlations between copepod abundance and water temperature or sampling depth, while other factors had a lesser influence. Our results suggest a strong effect of local circulation and currents on the spatial pattern of the copepod assemblages in the study area. This study may be useful for future biomonitoring in the south-eastern Barents Sea.

It is claimed that oceanic hydrothermal vents (HVs), particularly the shallow water ones, offer particular advantages to better understand the effects of future climate and other global change on oceanic biota. Marine hydrothermal vents (HVs) are extreme oceanic environments that are similar to projected climate changes of the earth system ocean (e.g., changes of circulation patterns, elevated temperature, low pH, increased turbidity, increased bioavailability of toxic compounds. Studies on hydrothermal vent organisms may fill knowledge gaps of environmental and evolutionary adaptations to this extreme oceanic environment. In the present contribution we evaluate whether hydrothermal vents can be used as natural laboratories for a better understanding of zooplankton ecology under a global change scenario.

Bioaccumulation by zooplankton is the outset for persistent organic pollutants that enter the marine food chain. Owing to a full spectrum of anthropogenic activities, the Gaoping waters of southwestern Taiwan are exposed to large quantities of polybrominated diphenyl ethers (PBDEs). However, information on these contaminants in zooplankton in this study area is lacking. In this study, we analyzed 19 PBDE congeners concentrations in 36 zooplankton samples from the Gaoping waters. A high variation in the total PBDE concentrations in zooplankton (from not detected to 1415 ng g−1 dry weight) was found, with the highest PBDE levels being recorded near the entrance of the Kaohsiung Harbor (KH). Significantly higher levels were noted for the KH transect than for the Gaoping River estuary (GR) and Fengshan Township (FS) transects, indicating that PBDE inputs originate from the ocean sewage outfalls. BDE-15 (43%) and BDE-209 (16%) were the predominant PBDE congeners in the zooplankton. Our results suggest that anthropogenic activities might predominantly contribute to significantly high PBDE concentrations. The traditional food web may easily transport these higher levels of PBDEs in zooplankton to higher trophic levels of marine organisms, since the Gaoping waters serve as essential nursery and spawning grounds for invertebrates and fishes.

Global warming is increasing the frequency and severity of the marine heat waves, which poses a serious threat to the marine ecosystem. This study analyzes seasonal and interannual dynamics in the abundance and structure of the mesozooplankton community in Sevastopol Bay based on bi-monthly routine observations over 2003–2014. The focus is on the impact of the summer 2010 marine heat wave (MHW2010) on crustaceans belonging to different ecological groups. As a response to the MHW2010, three warm-water species (O. davisae, A. tonsa and P. avirostris) exhibiting the maximum seasonal density in latter summer showed a sharp increase in the annual abundance and their share in the mesozooplankton community. The increase in the annual abundance in 2010 of the eurythermal species P. parvus and P. polyphemoides exhibiting seasonal peaks in spring and autumn is not related to the MHW2010 but can be explained by a rise of temperature in the first part of the year. O. davisae and A. tonsa showed the most pronounced response among the species to the MHW2010, confirming that non-native species exhibited great flexibility as an adaptive response to environmental changes, especially in the case of climate warming. Among crustaceans observed in this study, O. davisae can be considered as an indicator of the environmental conditions associated with the warming of the Black Sea and the Mediterranean basin as a whole.

The active carbon flux mediated by diel vertical migration (DVM) of zooplankton is an important component of the downward carbon flux in the ocean. However, active fluxes transported by zooplankton DVM are poorly known in the South China Sea (SCS) and the Western Philippine Sea (WPS). In this study, active carbon fluxes in the SCS and WPS were evaluated on the basis of the data of mesozooplankton community and DVM at two stations of these areas. The mesozooplankton community in the SCS was obviously different from that in the WPS, and higher species number and abundance in the SCS were observed, which may be related to the higher chlorophyll a (Chl a) concentration and the wide gradients of temperature and salinity in this sea. Moreover, shallow depth Chl a maximum and strong thermocline were detected in the SCS, causing lower migration amplitudes of mesozooplankton in the SCS than those in the WPS. However, the migrant biomass of mesozooplankton in the SCS was 98.40 mg C m–2, higher than that in the WPS at 25.12 mg C m–2. The mesozooplankton active carbon flux in the SCS (4.64 mg C m–2⋅d–1) was also higher than that in the WPS (1.80 mg C m–2⋅d–1). The mesozooplankton active fluxes were equivalent to 8.3 and 8.1% of the total flux (active flux plus passive flux) of the SCS and WPS, respectively, and they play an important role in the biological pump functioning in the two regions.

A significant sea surface temperature increase has been reported for the Southwestern Atlantic Ocean between 20° S-50° S over the last decades. Zooplankton organisms are highly sensitive to temperature rise. They play a very important role in marine ecosystems by providing the main pathway of energy transfer from primary producers to consumers. Seasonal and interannual (2000-2017) variability of metazooplankton in relation to environmental changes, particularly temperature, were analyzed at the EPEA station (38° 28′ S-57° 41′ W). Copepods, appendicularians, cladocerans, chaetognaths, and lamellibranch larvae were identified and quantified. Temperature exhibited a positive interannual trend during the series, whereas the Simpson parameter showed a decreasing tendency and salinity remained almost constant. Adults, copepodites, and nauplii of small copepods belonging to Oithonidae (mostly Oithona nana) and Paracalanidae-Clausocalanidae families dominated the metazooplankton community during the study period. Three groups of taxa with different seasonal patterns of variability were clearly identified. Members of Oithonidae exhibited positive interannual trends, whereas lamellibranch larvae and Calanidae showed negative interannual trends. A direct influence of temperature anomaly on these changes is suggested as well as possible indirect effects of this anomaly upon zooplankton through different phytoplankton fractions. Under the current scenario of climate change, the maintenance of this time-series becomes crucial in order to evaluate the eventual transfer of the environmental variability to the local food webs through planktonic organisms.

The Yellow Sea Cold Water Mass (YSCWM), one of the most vital hydrological features of the Yellow Sea, causes a seasonal thermocline from spring to autumn. The diel vertical migration (DVM) of zooplankton is crucial to structural pelagic communities and food webs, and its patterns can be affected by thermocline depth and strength. Hence, we investigated zooplankton community succession and seasonal changes in zooplankton DVM at a fixed station in the YSCWM. Annual zooplankton community succession was affected by the forming and fading of the YSCWM. A total of 37 mesozooplankton taxa were recorded. The highest and lowest species numbers in autumn and spring were detected. The highest and lowest total densities were observed in autumn (14 464.1 inds./m3) and winter (3 115.4 inds./m3), respectively. The DVM of the dominant species showed obvious seasonal variations. When the YSCWM was weak in spring and autumn, most species (e.g. Paracalanus parvus, Oithona similis, and Acartia bifilosa) stayed above the thermocline and vertically migrated into the upper layer. Calanus sinicus and Aidanosagitta crassa crossed the thermocline and vertically migrated. No species migrated through the stratification in summer, and all of the species were limited above (P. parvus and A. crassa) or below (C. sinicus and Centropages abdominalis) the thermocline. The YSCWM disappeared in winter, and zooplankton species were found throughout the water column. Thus, the existence of thermocline influenced the migration patterns of zooplankton. Cluster analyses showed that the existence of YSCWM resulted in significant differences between zooplankton communities above and below the thermocline. [ABSTRACT FROM AUTHOR]