Search

Streptococcus agalactiae is one of the main aetiological agents in large-scale mortalities of tilapia, having caused major economic losses to the aquaculture industry in recent years. This study describes the isolation and identification of the bacteria from cage-cultured Etroplus suratensis that experienced moderate to severe mortalities in Kerala, India. Gram-positive, catalase-negative S. agalactiae was identified from brain, eye and liver of the fish by antigen grouping and 16S rDNA sequencing. Multiplex PCR confirmed that the isolate belonged to capsular serotype Ia. Antibiotic susceptibility tests showed that the isolate was resistant to methicillin, vancomycin, tetracycline, kanamycin, streptomycin, ampicillin, oxacillin and amikacin. Histological sections of the infected E. suratensis brain revealed infiltration of inflammatory cells, vacuolation and meningitis. This report is the first description of S. agalactiae as a primary pathogen causing mortalities in E. suratensis culture in Kerala.

Bacteria play a central role in the degradation of phytoplankton-derived dissolved organic matter (P-DOM) particularly in algal-blooming aquatic systems; yet our understanding of the interaction between bacteria and P-DOM is still poor. We supplied differential P-DOM that varied in concentration and molecular weight (released from distinct phytoplankton collected from blue-green algal-blooming grass carp Ctenopharyngodon idellus farming ponds) to similar aquatic bacterial communities (isolated from non-blooming grass carp ponds), to explore how P-DOM affects bacterial community dynamics and to identify the most responsive degrading taxa using UV-visible absorption spectroscopy and high-throughput sequencing. Bacterial cultures all had similar degradation effects upon P-DOM, causing decreases in its concentration but increases in its molecular weight and aromaticity. In contrast, bacterial compositional changes varied primarily depending on P-DOM molecular weight, and Bacteroidia taxa were mostly affected, appearing more adapted to metabolize high-molecular-weight P-DOM. Nevertheless, most of the degrading taxa were recurrent and typically members within Gammaproteobacteria and Bacilli, indicating substrate-controlled bacterial responses induced by P-DOM. Network analysis revealed that bacterial communities harbored relatively low-abundant degrading members rather than dominant ones as keystone taxa, which presented simultaneously crucial microbial connections within communities and strong associations with environments and therefore played an over proportional role in maintaining community stability and functioning. Moreover, the keystone taxa may be generalists, and their ecological attributes can be described by oligotrophs that correspond to the K-strategists. Generally, this study implied a pivotal role of Gammaproteobacteria, particularly Pseudomonas, in P-DOM biodegradation, most probably in algal-blooming aquatic environments.

Human-induced habitat modifications can severely impact the biology and behavior of wild species. Drifting fish aggregating devices (DFADs), used by industrial purse-seine tropical tuna fisheries, significantly increased the number of floating objects found in the open ocean, with which tropical tuna associate. This habitat change has raised concerns over the risk of modifying the behavior and altering the biology of tuna and other associated species (the so-called ecological trap hypothesis). Relying on a time-series from 1987-2019 of more than 25000 length-weight samples collected in the western Indian Ocean, we reject the hypothesis that the body condition (Le Cren’s relative condition factor, Kn) of yellowfin tuna Thunnus albacares decreased concurrently with the increased number of DFADs. This result suggests the absence of negative long-term impacts of DFADs on the condition of tuna. As other factors may have counteracted possible negative effects of DFADs, we recommend long-term monitoring of the habitat along with biological and behavioral parameters of tunas to detect any critical change.

The north coast of the South Island, Aotearoa New Zealand, is a region with complex bathymetry and biogeochemistry, where oceanographic variability gives rise to very different local environments at fine scales. This variation also influences the region’s isoscape, providing the ability to assess the fine-scale foraging behaviour of top-level marine predators through isotope analyses. Hector’s dolphin Cephalorhynchus hectori hectori, an endemic coastal dolphin, is resident of the north coast of the South Island, but there is limited information describing its foraging ecology and population dynamics. We analysed carbon and nitrogen stable isotope ratios of skin samples (n = 111) from Golden Bay in the west (n = 14), and Queen Charlotte Sound (n = 41) and Cloudy Bay (n = 56) in the east, to investigate spatial variation in isotope values and niche space, found significant differences between the 2 regions. This is likely driven by a combination of differing prey distributions, underlying oceanographic variability, and varying isotopic baselines that may act as an ecological boundary preventing movement between the 2 regions. The isotopic niche space between the west and east differed, but within the east, Queen Charlotte Sound was a subset of Cloudy Bay. This suggests a common prey source and possible movement of individuals between Queen Charlotte Sound and Cloudy Bay. This research highlights the value of stable isotope analysis to investigate regional-scale variation of top-level marine predators and can provide insight into environmental factors that influence resource use.

The global ocean is expected to both acidify and warm concurrently; thus, multiple-stressor manipulative experimentation is an emergent area of study that ultimately aims to examine the individual and interactive effects of these factors on marine organisms. We characterized the physiological responses to acidification and warming of the intertidal grazer Lottia scutum, and examined how these ocean change variables influenced predator-prey dynamics with Evasterias troschelii, a key sea star predator. Specifically, we conducted a laboratory experiment where we exposed limpets to factorial combinations of temperature (11 and 15°C) and pH (7.6 and 8.0), and measured effects on thermal tolerance, metabolic rate, cortisol concentrations, and behavioral responses to the predator. We found that ocean warming (OW) decreased the critical thermal maxima (CTmax) and increased cortisol levels in L. scutum, whereas ocean acidification (OA) increased the mass-specific metabolic rate in this species. Additionally, we found that there was no significant effect of OA or OW on the anti-predator behavior of L. scutum when exposed to E. troschelii. These results highlight the need for future studies to integrate multidisciplinary experimental designs (i.e. behavior and physiology) that span multiple levels of biological organization to make ecologically relevant predictions for how marine organisms will respond to ocean change.

Settlement dynamics and post-settlement mortality of sessile invertebrates is a black box in marine benthic invertebrate ecology. Most studies capture recruitment (i.e. survival of an individual until the researcher returns) rather than the in situ settlement timing, growth, and survival of newly settled sessile invertebrates. Quantification of settlement is labor-intensive and nearly impossible in remote habitats. Using the prototype camera system CATAIN (CAmera To Analyze Invertebrates), we have a glimpse into this important transitional period. CATAIN photographs the underside of its endcap (which acts as a settlement panel) on a sub-daily time scale, capturing settlement, growth, and post-settlement mortality in sessile invertebrates. In this study, image analysis was used to track individuals of 4 species every 4 h and explore fine-scale temporal dynamics of benthic invertebrates living in Woods Hole, Massachusetts, USA, over a 1 yr period. The goal of this study was to identify settlement rather than recruitment of common sessile species, as well as determine their early post-settlement mortality to better understand the relationship between settlement and recruitment. Beyond tracking seasonality of settlement, we found relationships between environmental factors (temperature, tidal phase, time of day) and settlement timing. We also found different growth rates between temperatures for 1 species. There were variable patterns of post-settlement mortality among species and lower mortality overall than reported by previous studies. This study demonstrates CATAIN as a promising research tool and investigates previously unknown early life-history characteristics of 4 common subtidal benthic invertebrates.

Soft-bottom intertidal systems are valuable due to the ecosystem services they provide. Although these systems are normally subjected to highly variable environmental conditions, disturbances have become more frequent due to increases in anthropogenic pressure. Sea level rise (SLR) may generate changes in the ecosystem functioning of intertidal systems and in the ecosystem services they provide. In the Argentinean coast (SW Atlantic), SLR analysis shows trends similar to the global ones. It is not known how disturbances may affect the activity of benthic communities and the associated ecosystem functions. Therefore, through a field experiment at the marsh-mudflat edge in northeastern Argentina, we evaluated the effect of increased inundation time on bioturbation intensity, detritus decomposition and microphytobenthic primary production. Sediment physicochemical parameters (pH, temperature, water content and organic matter) were also measured. The results showed that increased inundation time had no effect on microphytobenthic primary production or bioturbation intensity in summer. Nevertheless, inundation time increased the burrowing activity of the intertidal crab Neohelice granulata in winter and spring and greatly decreased the variability in Spartina densiflora decomposition and organic matter content. In the context of a changing world due to global climate change, reduced variability in ecosystem functioning could indicate a decline in ecosystem resilience. As a consequence, vital ecosystem functions could be altered or lost, thus impacting the ecosystem services they deliver.

Resource availability is a key factor driving marine bird movements and distributions, but direct information on prey availability is difficult to obtain at relevant scales. We present novel methods for describing multi-scale trophic associations, combining movement analyses of marine birds with estimates of forage fish surface aggregations from digital aerial survey data and species occupancy from bottom trawl survey data. We analyzed satellite telemetry data from northern gannets Morus bassanus, red-throated loons Gavia stellata, and long-tailed ducks Clangula hyemalis in the US Atlantic during the non-breeding period. Using discrete-time hidden Markov models to distinguish area-restricted (i.e. putative foraging) from transit movements, we examined how environmental factors influence movement, and how forage fish species distributions and surface aggregations influence habitat use by gannets and loons that have greater dietary reliance. Our results suggest that chlorophyll a concentration significantly affected movement behavior across species, highlighting the importance of higher-productivity areas around estuaries during colder months when regional productivity is low. Though variable across species and seasons, spatial cross-correlation analysis revealed that herring species (Family Clupeidae), including Atlantic menhaden Brevoortia tyrannus, may be important resources; it also showed positive spatial correlations with forage fish aggregations. This suggests that prey patch dynamics and factors driving aggregation formation may be as important as species composition. However, spatial patterns were generally low (

Managing human impacts on marine mammal populations depends on understanding their distributions in space and time. Knowledge of these distributions is becoming increasingly important due to offshore energy development and climate-induced shifts in oceanic habitat. Most models assessing pelagic marine mammal abundance and distribution primarily use ocean surface or ocean floor variables as proxies for water column habitat. Here, we used a ship-based marine mammal sighting survey to test the utility of echosounder-based predictive variables for modeling marine mammal distribution and abundance. We assessed the distribution of 7 marine mammal taxa and 3 feeding guilds along the shelf break off the northeast USA relative to prey structure derived from acoustic data. We classified prey into 4 categories: (1) fish with swimbladders; (2) small resonant bubbles as phytoplankton, fish larvae, and gelatinous zooplankton; (3) fluid-like scatterers such as krill and copepods; and (4) fish with no swimbladder. We quantified the spatial structure of prey by calculating backscattering strength, location, dispersion, occupied areas, evenness, and aggregation. Spatial resolution along the survey track line was set to bins 1000 m in distance and either 50 or 200 m in depth. We then built generalized additive models (GAMs) using these acoustically derived variables to explain marine mammal distribution. The resulting GAMs explained between 9 and 38% of deviance, with model fit often reflecting aspects of foraging depth and prey preference. This approach could contribute to improved management through more accurate species distribution models that employ direct measurements of prey.

The historical ecology and foraging behavior of many apex marine predators are poorly known. This includes highly mobile pelagic species such as billfish (Xiphiidae and Istiophoridae), which have long held cultural significance for coastal peoples. In California’s Santa Barbara Channel Region, Chumash people have hunted billfish for >2000 yr, providing a deep historical record of these species. We present bulk tissue δ13C and δ15N data for 15 Late Holocene archaeological swordfish Xiphias gladius and 1 striped marlin Kajikia audax previously identified to species through collagen fingerprinting. When compared to data sets of modern northeastern Pacific and archaeological Gulf of Maine swordfish, we identified significant overlap in the isotopic values of modern and archaeological swordfish from the Pacific, indicating that pre-industrial swordfish were reliant on food webs of the North Pacific Subtropical Gyre and the California Current System. We also identified differences in the isotopic composition of swordfish captured by island vs. mainland communities, with swordfish remains from mainland sites having lower and more variable δ13C values, potentially indicating different source populations. The isotopic range of swordfish from California archaeological sites was much broader than those from the Gulf of Maine, suggesting a wider range of habitats used by Pacific swordfish. Our results provide important pre-industrial data for an apex marine predator.

Rocky reefs throughout the temperate zone are dominated by large brown algae, which are major foundation species and ecosystem engineers. There is usually an ecological bottleneck at the early life stage of such algae when they are vulnerable to a wide range of stressors. A large earthquake that affected the coastline of southern New Zealand highlighted the combined effects of sudden changes to multiple stressors on large algal assemblages. In particular, the regime of temperature, sediment and light suddenly changed as the coastal platform was lifted, and sediments from the catchment occluded the light environment of nearshore waters. Here we tested the effects of these stressors on early survival and growth of 3 formerly dominant species—the fucoids Landsburgia quercifolia and Durvillaea antarctica and the laminarian Lessonia variegata—over 100 d using a culture laboratory. After 42 d, interactive effects were found for growth of all species. Decreasing light and increasing temperature had the greatest negative effect on L. variegata and D. antarctica growth. Growth was minimal at the lowest light treatment (PAR: 16 µmol m-2 s-1) for all species, but often least growth was found at the highest sediment treatment (PAR: 32 µmol m-2 s-1). L. quercifolia was resilient to increasing temperature, whereas survival and growth decreased with increasing temperature for D. antarctica and L. variegata. These results are highly suggestive of the coincident influences of major stressors on the post-earthquake marine ecosystem. These results also highlight that recovery of large brown algae following disturbance events is likely to be slow due to an increase in coastal sedimentation and extreme water temperature.

Sediment transport on salt marsh platforms is usually brought about through storm events and high tides. At high latitudes, ice-rafting is a secondary mechanism for sediment transport, redistributing sediment from tidal flats, channels, and ponds to marshland. In January 2018, winter storm Grayson hit the North Atlantic coast, producing a large storm surge and a significant decrease in temperature. The Great Marsh in Plum Island Sound, Massachusetts, USA, experienced an unprecedented sediment deposition due to ice-rafting, burying marsh vegetation. Plant vegetation recovery was investigated in 17 sediment patches, dominated by Spartina patens, Distichlis spicata, Juncus gerardi, and S. alterniflora. The analysis was carried out considering the number of stems and stem height for each vegetation species. D. spicata firstly occupied bare patches, while S. patens, once smothered by sediment, regrew slowly. The number of stems of S. patens inside the sediment patches recovered, on average, after 2 growing seasons. The number of J. gerardi stems was not significantly affected by ice-rafted sediment deposition. S. alterniflora dynamics were different depending on physical and edaphic conditions. At some locations, S. alterniflora did not recover after sediment deposition. The deposition of the sediment layer had a positive effect on vegetation vigor, increasing stem height and maintaining high stem density. The results suggest a beneficial effect of sediment deposition not only for marsh accretion, but also for marsh vegetation growth, both of which are fundamental for marsh restoration.

Climate change and industrial activities are leading to significant ecological changes in the Eastern Canadian Arctic, with consequences for top predators, including ringed seals Pusa hispida. However, there remains a limited understanding of habitat use, constraining an understanding of the impacts of change on this culturally valued pinniped. A total of 20 ringed seals from 2 areas in Labrador with different geomorphic attributes (Saglek Fjord in the North, and Lake Melville, an estuarine ‘fjard’ in the South) were equipped with satellite-linked transmitters to characterize behaviour states, home ranges, core use areas and environmental variables. Lake Melville-tagged seals had a smaller home range than Saglek Fjord seals (84968 vs. 196886 km2). There was little spatial overlap in the home ranges (10%) and core use areas (0%) between the 2 areas, which were separated by 572 km. Lake Melville seals spent more time in a transiting state during open water conditions (26%) than during ice-covered periods (9%), probably due to an influence of sea ice concentration; they also spent more time in the area in which they were tagged (72%) than did Saglek Fjord seals (36%), increasing the risk of exposure to local contaminants associated with hydroelectric developments. Our results suggest that ringed seals in Lake Melville have better feeding opportunities but may be more vulnerable to changing ice conditions and contaminants compared to seals in Saglek. These results will support the development of a planned culturally based Marine Protected Area in Nunatsiavut and can inform efforts to remediate contaminant sources in the region.

Assessing the total lipid content (TLC, expressed as % wet weight, WW) and constituent fatty acid (FA) composition (expressed as % of total FA) in marine organisms provides vital knowledge about the transfer of energy and essential nutrients from primary producers to higher-order consumers, including humans. To obtain a broad understanding of marine lipid dynamics, we used information from more than 470 species of Australian and Southern Ocean marine consumers spanning across the food web, from secondary to apex predators, sampled over a 30 yr period (1989 to 2019). Taxa group, trophic guild, and collection period were found to be the most influential drivers of variability in 4 key variables (TLC, docosahexaenoic acid [DHA, 22:6n-3], eicosapentaenoic acid [EPA, 20:5n-3] and arachidonic acid [ARA, 20:4n-6]). Highest TLC was observed in marine mammals and mid-trophic consumers, highest DHA occurred in fish and apex predators, highest EPA occurred in krill and other lower-level consumers, and highest ARA was present in rays and other apex predators. Horizontal habitat type was also an important driver with significantly higher TLC, EPA, and DHA found in samples from oceanic and pelagic habitat types, whilst coastal habitat samples had significantly higher ARA. Generalised additive mixed models determined that there were regional spatial patterns and interannual trends for all variables over the 30 yr period across all taxa groups. This study provides new understanding of the spatial distribution, temporal trends, and drivers of lipid and essential fatty acids (EFA) in marine ecosystems in the southern hemisphere.

Microalgae-associated bacteria affect the dynamic succession of microalgal communities. The composition of the bacterial community of a single species of microalgae is conserved, and the same bacterial species can be found in different algal phycospheres. However, it is unknown whether the same bacterial species, widely distributed in the phycosphere, carries out the same interactions with different microalgae. Here, the interactions of Sulfitobacter pseudonitzschiae strain H46 and 4 microalgae, Phaeodactylum tricornutum, Cylindrotheca closterium, Heterosigma akashiwo, and Chattonella marina, were investigated using a co-cultivation method. The results showed that H46 had a significant inhibitory effect on the growth of C. marina but no effect on the other 3 microalgae. Further study revealed that H46 produced heat-resistant algicidal metabolites to lyse C. marina specifically, and secreted indoleacetic acid (IAA), which promoted the growth of the other 3 microalgae. Dimethylsulfoniopropionate (DMSP), produced by P. tricornutum, C. closterium, and H. akashiwo, can be utilized by H46. However, DMSP was not detected in C. marina, suggesting that S. pseudonitzschiae promotes the growth of DMSP-producing microalgae and kills DMSP-deficient microalgae. We speculate that DMSP may be a regulatory substance driving distinct algae-bacteria interactions, which is of great ecological significance for regulating the structure of microalgal communities.

The ability of organisms to detect, locate and navigate to resource patches is modified by the surrounding landscape. Green sea urchins Strongylocentrotus droebachiensis in barren grounds exist in a food-limited state and are subject to intense competition. Rapid detection and consumption of resource patches, particularly pieces of macroalgae from adjacent algal beds, are key in determining individual growth, survival and reproductive success. Detection and movement to resource patches requires moving through a heterogeneous benthic seascape composed of rocky and sandy patches, presenting different degrees of resistance to movement. We used time-lapse photography to describe the foraging behaviour of urchins in relation to the presence of a key resource subsidy (drift kelp) and different benthic seascapes. We demonstrated that urchins could detect the presence of drift kelp in barren-ground habitats and alter their movement behaviour in response, but did not exhibit the ability to directionally navigate towards kelp in field conditions. Seascapes with increased proportions of rocky substrata facilitated increased movement in response to the presence of drift. Moreover, urchin foraging behaviour was temporally variable, with no response to the presence of drift in early spring (May). This indicates not only that interpretations of observations of urchin behaviour must take intrinsic and extrinsic seasonal dynamics into account, but that extrapolating results to explain larger-scale patterns and processes must include both spatially explicit subtidal seascapes and temporal dynamics. In many temperate and boreal regions, this indicates the need for increased subtidal benthic research in the fall and winter.

Marine communities are subject to alterations in environmental conditions, due to both natural variability and climate change. For instance, a rapid increase in sea surface temperature (SST) can modify spatial distribution patterns and abundances of reef fishes and therefore alter the overall diversity, structure, and functioning of these communities. Trait-based approaches may accurately detect community responses to such environmental changes, because species traits should reflect resource and habitat requirements. Here, we investigated temporal variability in reef fish trait composition and thermal affinity and assessed whether shifts are linked to recent ocean warming. We combined species traits related to feeding, growth, and survival with abundance data on reef fish from underwater visual census at 7 islands of the Southwestern Atlantic subtropical transition zone. All islands exhibited gradual trait reorganization from fish assemblages dominated by large-size species at the beginning of the time period to small, cryptobenthic species towards the end. The temporal changes in community weighted mean traits and the community thermal index were related to SST, indicating a numerical response of species to climatic variations. Tropical species are slowly becoming more abundant over time, while temperate species are becoming less abundant, reflecting an initial change in fish composition in this transition zone. These results have ecological implications leading communities to a faster turnover, lower food-chain complexity, and higher vulnerability to change. We highlight the importance of integrating traits and abundance time series data for a holistic understanding of reef dynamics and community responses to environmental variation, including global warming.

White spot syndrome virus (WSSV), which causes white spot disease, is one of the notoriously feared infectious agents in the shrimp industry, inflicting estimated production losses world-wide of up to US$1 billion annually. Cost-effective accessible surveillance testing and targeted diagnosis are key to alerting shrimp industries and authorities worldwide early about WSSV carrier status in targeted shrimp populations. Here we present key validation pathway metrics for the Shrimp MultiPathTM (SMP) WSSV assay as part of the multi-pathogen detection platform. With superior throughput, fast turn-around time, and extremely low cost per test, the SMP WSSV assay achieves a high level of analytical sensitivity (~2.9 copies), perfect analytical specificity (~100%), and good intra- and inter-run repeatability (coefficient of variation

Finfish aquaculture is playing an increasing role in global food provision, with accompanying increases in benthic impacts under intensive pen production systems. Deposited faeces under and near fish pens affect the seafloor environment and biogeochemical functioning. To maintain healthy coastal environments, many fish farms operate by alternating input and fallowing periods to allow benthic coastal receiving environments to recover from excess organic matter inputs. Here, we used flow-through annular flume mesocosms to simulate sustained organic matter inputs to the benthos with a subsequent fallowing period of no inputs. To quantify the effects of excess organic matter loading on benthic receiving environments, we carried out repeated closed-system flux studies to quantify the benthic carbon mineralisation processes, with a focus on benthic oxygen, inorganic and organic carbon, nitrogen, phosphate, and sulphide fluxes, along with the redox state throughout the input and recovery period. We found that recovery periods were input-dependent, with parameters requiring longer fallowing periods to recover following larger inputs. While some benthic parameter fluxes such as dissolved organic carbon, sulphide, and ammonium returned to their pre-input state relatively rapidly (1-2 mo) following cessation of inputs, others such as sediment oxygen demand, ammonium, and redox required longer (>7 mo) to recover. Our results suggest that in situations where the benthic macrofaunal community has been severely impaired, extended fallowing periods may be required in order to permit the biogeochemical composition of the seabed to return to a more natural state, with implications for farm-consenting permits and planning as well as operational fallowing practices.

Implantation of ultrasonic pingers in fish is invasive in nature, as it bisects epidermis and skin tissues, with negative health impacts on the individual. Taking Korean rockfish Sebastes schlegelii as a model species, we compared the difference between using surgical sutures and disposable-staple sutures so as to minimize the impact caused by implantation. The results showed that (1) the critical swimming speed of S. schlegelii changed significantly 2 h after surgery but did not change significantly 1 d after the operation; (2) both suture methods can effectively close the wound; and (3) it takes less time to suture the wound with disposable skin staples than with a surgical needle. The abdominal incisions of the experimental fish were clean, the fish showed no inflammation or necrosis after suture by the 2 methods, and they remained healthy for 7 d after operation. We conclude that disposable skin staples are well suited for minimally invasive surgical suturing.

Top predators play key roles within their respective ecosystems. However, their ability to adjust their behaviors in response to changes in environmental conditions and food web structure, which is important in light of climate change and continued anthropogenic disturbance, is still unclear in many ecosystems. We combined stomach content and stable isotope analyses to study the trophic ecology and plasticity of the dominant top predators—the bull shark Carcharhinus leucas and the alligator gar Atractosteus spatula—in 2 estuaries of the northwestern Gulf of Mexico. Both species showed a high degree of prey preference and predominantly fed on mugilids. Juvenile bull sharks were also demersal foragers with a high relative trophic position (TP ≈ 4), feeding heavily on sea catfishes (Bagre marinus and Ariopsis felis) and red drum Sciaenops ocellatus. Comparatively, alligator gars were ambush foragers with TP ≈ 3 that targeted schools of gulf menhaden Brevoortia patronus. Sharks and gars exhibited overlap in their trophic interactions, indicating potential competition for prey, but our results highlight mechanisms that mitigate competition, including spatial partitioning and intraspecific variability. The diets of both species also appeared highly flexible, with individuals able to adjust to spatiotemporal shifts in prey availability. These findings suggest the bull shark and the alligator gar may be somewhat resilient to the ecological change associated with climate change and anthropogenic disturbances and highlight the utility of combining different approaches to refine our understanding of the ecological roles of top predators.

We investigated how local and global stressors affect coral reefs in situ by taking advantage of a latitudinal gradient in the central equatorial Pacific driven by El Niño-Southern Oscillation, where the past frequency of heat stress decreases away from the equator. We compared benthic communities at 40 sites across 4 atolls in the Gilbert Islands, namely in Kiribati (Tarawa and Abaiang) and the Republic of the Marshall Islands (Majuro and Arno), representing gradients in local chronic human disturbance and past frequency of bleaching-level heat stress. A hierarchical clustering analysis found 3 groupings of benthic communities, corresponding to sites with (1) low human influence and frequency of heat stress, (2) low human influence and high frequency of heat stress, and (3) high human influence, suggesting that the effects of intense, ongoing local disturbance may mask the influence of heat stress on coral reef communities. The frequency of heat stress explained 8.0% of the differences in community compositions across all sites (PERMANOVA), while local anthropogenic stressors explained 16.2%, and the combined effects explained 7.0%. Interactions between stressors were multiplicative and acted synergistically to increase the percent cover of macroalgae and the stress-resistant coral Porites rus. The prevalence of P. rus at locally disturbed sites drives the positive relationship between local stress metrics and live coral cover. At the taxon level, half of the multiplicative interactions were antagonistic, suggesting that actions that reduce local stressors may help some coral taxa respond to climate stress, but possibly at the expense of other taxa.

Monitoring the first seaward migration of juvenile salmonids, known as smolts, is challenging because there is limited tracking technology suited to their small size. Nevertheless, for their management and conservation purpose, it is critical to understand this phase of their life cycle when they adapt to increased salinity, novel predators and new prey. Smolts of 2 species, Atlantic salmon Salmo salar and brown trout Salmo trutta, were acoustically monitored at 4 study sites, together with biotic and abiotic parameters, to estimate and explain their survival during their estuarine migration to sea. The 2 species exhibited different levels of survival during this seaward migration, with a higher survival for trout smolts. For both species, survival was similar among 3 of the 4 sites. Migration speed and migratory distance influenced smolt estuarine survival, but body length, body condition, sex, age, and environmental parameters (temperature, salinity, dissolved oxygen) did not. Migration speed, potentially reflecting smolts’ capacity to avoid predators or escape dangerous areas, had a positive effect on their survival. Increased distance negatively influenced estuarine survival, which could lead to lower survival rate in the River Frome Estuary where orientation is more difficult for smolts due to widely separated environmental cues. Overall, smolt survival through estuaries was estimated between 51 and 97% among 4 populations, suggesting that estuaries are variably challenging environments for migrating smolts, accounting for non-negligible early marine survival. Understanding which estuaries have low survival and why is imperative to prioritise management actions.

At least 4 species of callichirid shrimp coexist in the shallow marine settings of San Salvador Island, an isolated, small platform of the all-carbonates Bahama Archipelago, implying that interspecific competition or trophic niche segregation occurs between these shrimp species. Carbon and nitrogen stable isotope analyses were conducted on soft tissues of 3 callichirid species, Neocallichirus cacahuate, N. grandimana, and N. maryae, to determine the food sources for each species. These analyses revealed that the isotopic trophic niches for these 3 species do not overlap. The most important food source for all 3 species was manatee grass Syringodium filiforme. The second most important food source for N. cacahuate and N. grandimana was drifting seaweed Sargassum sp., whereas that for N. maryae was turtle grass Thalassia testudium. These food-source adaptations likely contribute to the high species diversity of callichirid shrimp in tropical settings such as those found on San Salvador Island.

Structured habitats can offer prey refuge by reducing the encounter rates between predators and prey. However, structured habitats can also reduce predator-predator encounters, thereby dampening intraspecific interactions and increasing overall prey consumption. In this study, we tested whether intraspecific competition among Sayi mud crabs Dyspanopeus sayi foraging on mussel Mytilus edulis prey was modified by the density of mimicked eelgrass Zostera marina shoots. Predation was measured in 3 predator densities (1, 3, or 6 predators) and 1 of 5 levels of shoot density. We found no impact of Z. marina on intraspecific competition, regardless of predator density. Intraspecific competition was weak; per capita crab consumption decreased as predator density increased and became significantly reduced when predator density increased from 1 to 6. However, there was no evidence of non-additive predator density effects when predator abundance doubled from 3 to 6 predators. Our results also indicate that eelgrass structure may not offer the sessile prey M. edulis refuge when one or more D. sayi predators are present. Further exploration is needed to understand whether the lack of a structure effect is due to our use of sessile rather than mobile prey as used in other studies. Predator density and not structural density influenced intraspecific competition among D. sayi predators when they were foraging for M. edulis in mimicked Z. marina shoots.

A strong negative relationship has been observed between calf production of eastern North Pacific gray whales Eschrichtius robustus and Pacific Arctic sea ice area with the exception of 2 potentially anomalous periods: 2013-2014 and 2017-2019. Sea ice may play a role in reproductive variability by blocking gray whale access to foraging hotspot habitats. We tested this ‘sea ice exclusion’ hypothesis using complementary aerial survey and moored hydrophone data sets that together provide broad spatial and temporal coverage. A negative relationship (generalized additive model, p < 0.001) was found between gray whale aerial counts and ice concentration in the northeast Chukchi Sea (2008-2019), with a nonlinear increase in negative slope above 45-55% concentration. A comparison of distribution patterns between years further indicated the absence of sightings within northern Bering and northeastern Chukchi foraging hotspots during years with delayed ice break-up versus years with an early-to-average ice retreat. Passive acoustic recordings likewise showed the near-absence of detections during periods of dense ice cover and indicated a strongly positive relationship between ice break-up dates and the timing of acoustic detection onset. Together, these analyses point to the important role of sea ice in gray whale distribution, habitat use, and phenology. However, a relatively consistent 10-15 d lag observed between ice break-up and acoustic onset dates suggested that the mechanism(s) underpinning gray whale interactions with sea ice may be more complex than simply ‘sea ice exclusion.’ Here, we propose ‘prey quality timing’ as a potential alternative hypothesis that warrants further investigation.

When resources are finite, individuals optimize energy allocation between survival and reproduction to maximize fitness. As food becomes more limited within foraging ranges of breeding colonies, long-lived seabirds are predicted to increase time spent foraging, and chick growth, breeding success and ultimately adult survival, will be reduced. Across 3 years (2017, 2019, 2020), we investigated responses of breeding razorbills Alca torda in coastal Newfoundland, Canada, to inter- and intra-annual variation in biomass of the primary forage fish, capelin Mallotus villosus, which migrate from offshore into coastal regions during the summer to spawn. We combined capelin biomass (hydroacoustic surveys) with chick-rearing razorbill foraging effort (GPS, temperature-depth recorders), dietary proportions (blood δ15N and δ13C) and adult/chick body condition. Peak capelin biomass was near the long-term average for the study area in 2017 (0.109 g m-2) and 2019 (0.098 g m-2) and the lowest on record in 2020 (0.002 g m-2). In 2017 and 2019, razorbill foraging effort decreased after spawning capelin arrived inshore, but this decrease was not observed in 2020 (mean ± SE trip distance: 12.8 ± 2.8 km in 2017, 14.3 ± 1.7 km in 2019, 150.4 ± 25.2 km in 2020; number of dives per trip: 48.4 ± 11.8 in 2017, 385.8 ± 67.4 in 2020). Increased foraging effort during 2020 was associated with lower chick and adult body condition, likely due to parental birds flying farther and diving more to capture capelin. Findings suggest that lower capelin biomass observed in recent years may have long-term population-level consequences for razorbills and other seabirds in this region.

Ecological theory predicts that closely related species can coexist if they segregate in space, time, or diet to reduce competitive overlap when resources are limited. These differences in ecological niche are presumably driven by concomitant differences in morphology. The link between form and functional segregation may only occur at 1 period of the year, and while examining behavioural differences among closely related species across the whole annual cycle can answer this question, it is rarely tested. Here, we investigated niche partitioning between sister species within the puffin clade: tufted puffins Fratercula cirrhata with high wing loading and rhinoceros auklets Cerorhinca monocerata with low wing loading, breeding in sympatry on Middleton Island, Alaska. We collected data for horizontal movement, dive depth, and trophic ecology. Tufted puffins dived deeper, foraged closer to the colony during breeding, and migrated shorter distances relative to rhinoceros auklets. Examination of allometric patterns further revealed that puffins exceeded the predicted dive duration limit with exceptionally long dives. However, isotopic niches of the 2 species were very similar. Rhinoceros auklet breeding phenology was about 3 wk earlier than tufted puffin phenology, and breeding success during the study period was always higher for auklets than puffins. We conclude that the 2 species of sympatric puffin partitioned both in space and time throughout the annual cycle, illustrating how such partitioning can facilitate the coexistence of seabirds sharing apparently similar space.

Selecting optimal locations for mussel farming is vital for the optimization of production yield and for the minimization of environmental impact. Although predation by sea ducks may induce large stock losses and hence severe economic loss for mussel farmers, predation potential is rarely included in site-selection tools. In this paper we present a GIS-based spatial model predicting the potential of eider predation on blue mussel farms in Danish coastal waters. The model incorporates national survey data on eiders, as well as knowledge of eider behavior and habitat preferences, and was calibrated with predated/non-predated observations of eiders from 9 experimental mussel farms or test lines in Danish coastal waters. Except for 1 case study area, our model successfully confirmed a higher predation potential at test sites where predation had been observed. Our resulting predation potential map revealed potentials ranging from very low in inner parts of narrow estuaries to very high in more open coastal areas. Integration of the predation map into an existing site-selection tool showed that areas optimal for mussel growth were also associated with the highest modelled predation potential. Nonetheless, it was possible to identify areas having a very low potential of predation and only a 10% lower mussel production potential. These results underpin the potential for reducing production loss and increasing income by including predation potential in site-selection tools. In addition, the eider predation model can be used to identify and subsequently protect key foraging areas to support eider conservation.

Fish are thought to settle and recruit to shellfish and seaweed farms; however, there is little published evidence to support this assumption. Shellfish and seaweed farms increase structural complexity and epibiota productivity, which may attract settling fish larvae. In this study, fish settlement and recruitment patterns into 2 aquaculture habitats, mussel-kelp co-culture and mussel farm monoculture, were compared to 2 adjacent natural habitats, soft-sediment seafloor and rocky reef, within a settlement season. Standard monitoring units for the recruitment of fish (SMURFs) were used, as they are a common and reliable method for measuring temporal and spatial variability in fish settlement and recruitment among habitat types. The communities of fish species settling and recruiting to both sets of aquaculture and natural habitats were equivalent. This was most likely due to the artificial 3D structure of the mussel farm habitats functioning in a similar manner to the structural complexity of a rocky reef habitat. Further, there was indication that for at least the most abundant fish species, Fosterygion lapillum, the 2 aquaculture habitats were of sufficient quality to support growth from settlement to juvenile size classes (i.e. in mussel monoculture habitat 65% were newly settled in December, and 86% were of juvenile size class by February). Overall, these findings provide foundational quantitative evidence of the interactions that fish have with mussel farms and increases the understanding of restorative opportunities for aquaculture operations.

Photosynthetic picoeukaryotes (PPEs) are characterized by a reduction in cell and genome size but are free living, in contrast to many other organisms that have undergone such reductions. The relative abundance of PPEs in the oceans remains to be determined, as do the evolutionary imperatives behind their cell and genome reduction. Their enigmatic nature may be deciphered through metagenomics approaches; consequently, we utilized shotgun data from the Tara Oceans database to better understand both their ecological and genomic features. The clustering of meta-metabolomic networks constructed from shotgun data from 10 different sampling sites was influenced by the proportion of PPEs in the data sets. This, along with the relative abundance of RUBISCO sequences belonging to PPEs, indicates that they have a significant effect on oceanic meta-metabolism, emphasizing the evolutionary success of the streamlining strategy. Using rRNA sequences extracted from the shotgun data, a global oceanic distribution of PPEs showed little variation, including those lineages with reduced genome sizes. This indicates that genome and cellular streamlining is not an adaptation to environmental parameters but may rather be a community-driven effect. Lastly, and surprisingly given their role as primary producers, PPEs were found to comprise only 2 to 49% (17% on average) of all picoeukaryotes across 93 metagenomes. We show that contamination of the data set by eukaryotes with larger cell sizes is not responsible for the anomaly, and so the observation remains to be explained. The approaches described here allow us to draw a direct link between taxonomic composition and meta-metabolomic capacity, with implications for better understanding carbon fixation, biogeochemical cycling, and planetary self-regulation.

Monitoring is essential for efficient management of marine protected areas (MPAs) but often limited financially. Using low-cost stereo baited remote underwater video, we evaluated potential protection effects in the demersal assemblage of a marine reserve in European Atlantic temperate waters (southwestern Portugal). Due to a lack of before-MPA data, we compared multiple sites from the reserve inside and outside, investigated time trends, and assessed the potentially confounding effects of physical habitat. We found greater biomass of the legal-sized group (i.e. commercial above legal minimum landing size) inside the reserve than outside in the most recent year as opposed to the first year and a significant time increase in its abundance and biomass inside but not outside, indicating different trends in protection levels. On the contrary, biomass of the non-target group decreased significantly in both protection levels through time. One of the most targeted species, the legal-sized Diplodus sargus, reached significantly higher biomass inside than outside while also manifesting positive protection signs in abundance and length. Two legal-sized taxa showed no (Diplodus vulgaris) and negative (Mugilidae) protection responses, possibly due to low value and mobility of the latter. We detected positive responses in non-target wrasses Labrus bergylta and Symphodus spp., highlighting incidental fishing interest. Habitat did not interfere with protection effects. We suggest that community analysis based on stereo measurements renders sensitive protection indicators and offers a more thorough approach than prevailing abundance-focused analysis. The proposed low-cost monitoring solution can serve as a model to other MPAs.

Modelling potential impacts of salmon lice Lepeophtheirus salmonis on Atlantic salmon Salmo salar requires estimation of the levels that cause serious sub-lethal physiological impacts and direct mortality. Here we analysed results from existing laboratory experiments to identify 2 thresholds; the lower threshold (T1) estimates the level at which lice loads cause systemic sub-lethal effects on smolts likely to impact performance, and the upper threshold (T2) identifies the lice load causing direct mortality. T1 is an empirical value based on a catalogue of lice impacts according to impact type (superficial or systemic) and concentration, converted from a range of experiments. The onset of these indicators of welfare and behavioural impacts indicates T1 ≈ 0.08 lice g-1 of host. T2 represents 50% probability of onset of mortality under laboratory conditions quantified using a dose-response curve based on data collated from studies where mortality has occurred or not at specified lice concentrations. T2 ≈ 0.24 lice g-1 with a bootstrapped 95% confidence interval between 0.1 and 0.67 lice g-1. These thresholds offer both an amending of the current approach to the management of lice concentrations on fish in the form of a sub-lethal welfare threshold and further evidence to support mortality-based lice thresholds already in use.

Myxobolus zhaltsanovae n. sp., is described from the gills of gibel carp Carassius gibelio found during a survey of myxozoans from the watershed of Lake Baikal, Russia, based on morphological and molecular characterizations. Plasmodia of M. zhaltsanovae n. sp. develop extravascularly and measure 500-1000 μm long, 25-100 μm wide. The myxospore is circular to oval, measuring 13.23 ± 0.09 (11.3-14.8) µm (mean ± SD, range) in length, 10.19 ± 0.07 (9.1-11.4) µm in width, and 6.49 ± 0.12 (5.4-7.2) µm in thickness. Polar capsules are unequal and subspherical; measurements of polar capsules are: length 5.62 ± 0.06 (4.7-6.7), width 3.44 ± 0.04 (2.4-4.4) µm and length 3.42 ± 0.05 (2.5-4.1), width 1.94 ± 0.04 (1.3-3.3) µm. Phylogenetic analysis with the 18S rDNA gene shows M. zhaltsanovae n. sp. as a sister species of the subclade formed by M. musseliusae, M. tsangwuensis, and M. basilamellaris, which infect common carp Cyprinus carpio.

22 pages, 6 figures, 7 tables., Abrupt changes in environmental conditions in estuaries and coastal waters have direct (physiological) and indirect (through changes in water column stability) effects on planktonic microalgae. Understanding and quantifying these effects is important to improve harmful algal bloom predictive models. Dinophysis spp. (D. acuminata, D. acuta and D. caudata) and Alexandrium minutum produce toxins that are transferred through the food web (particulate) by filter feeders and also released in the seawater. These dinoflagellates cause lengthy harvesting bans in European aquaculture sites and affect marine life. The 4 species were exposed to different combinations of temperature (T) and salinity (S) to investigate their short-term response (days) to and their recovery (weeks) from T/S stress. Dinophysis species showed varying capacities to deal with sudden changes in S, from the most resilient D. acuminata, equally affected by T and S stress, to the less tolerant D. acuta, and in particular D. caudata, more affected by S than T stress. The euryhaline A. minutum thrived under all the T/S combinations assayed. Further experiments showed a similar rate of okadaic acid toxin production (pg cell-1 d-1) for the 3 Dinophysis species under different T/S conditions. In contrast, a significant increment of gonyautoxin 4 content per cell was observed in A. minutum with decreasing S without significant effects associated with T. Our results highlight the response to environmental (T/S) stress of 3 species of Dinophysis and A. minutum with specific adaptations to thrive in different sub-habitats of the Galician Rías, an estuarine/coastal upwelling system in NW Spain, This work was funded by the EU-INTERREG Atlantic Area project PRIMROSE (EAPA 182/2016) and a GAIN grant from the Innovation Agency of the Galician Government (Xunta de Galicia) for Galician Networks of Excellence (GRC-VGOHAB IN607A-2019/04), with the support of the CCVIEO Culture Collection of Micro algae from the Oceanographic Centre of Vigo (IEO, CSIC). M.S. acknowledges a pre-doctoral contract granted to the Spanish project DIANAS (CTM2017-86066-R), RETOS Programme, MINECO. This work is a contribution of the Uni dad Asociada de Microalgas Nocivas-VGOHAB group-IEO-CSIC

The marine benthos has been largely studied through the use of response traits that characterise species vulnerability to disturbance. More limited has been the specific use of effect traits that represent other species descriptors and that express ecosystem functions. On the sea floor, the benthos is a key ecosystem-engineering component for which functions can be relevantly derived from effect traits. This study provides a typology of sea floor functions based on an extensive data compilation of effect traits. We classified 812 benthic invertebrate species from the northeast Atlantic by 15 effect traits expressing substratum alteration and habitat creation. Cluster analysis identified 15 species groups that represented various epi- or endobenthic functions. Beyond function−habitat specificity, we show that soft sediment species exhibited broader functional niches in the trait space that increase multi-functionality, and were endowed with rare combinations of traits that expanded the functional extent of the species assemblage. As a consequence, soft sediments can host a higher functional diversity than hard substrata because a wider range of above- and below-substratum activities are possible in soft bottoms. Based on response traits documented for the same species and used to express vulnerability to natural or humaninduced disturbance, we then show that vulnerability within sea floor functions can be considerably variable. This can be a consequence of the independence between the evolutionary nature of response traits and the contingent engineering abilities of benthic species through effect traits. The paper provides theoretical and utilitarian clarifications on this trait dichotomy. Benthic invertebrate · Effect trait · Ecosystem engineering · Ecosystem function · Functional group · Functional diversity · Vulnerability

Microplastic (plastic particles Paramecium bursaria-Chlorella spp. association. To address how productivity, an important ecosystem service provided by photosymbiosis globally, could be affected, I also measured changes in photosymbiotic net productivity (net photosynthesis rate). To do so, I exposed the symbiosis to microplastics (microbeads extracted from commercial face wash) under laboratory conditions. My key result was that, compared with non-contaminated control cultures, the contaminated symbiosis demonstrated lower net productivity. This response raises concern for primary production rates in freshwater ecosystems contaminated with microplastics, adding to an established story of widespread degradation associated with microplastic pollution globally.

Multi-colony studies of breeding seabirds may provide insights into the mechanistic links between large-scale climate variability and local changes in prey availability. In the North Pacific, the Pacific Decadal Oscillation (PDO) is a dominant climate index characterized by contrasting patterns in sea surface temperature between the western and eastern North Pacific. To examine how inter-annual variability in the PDO affects rhinoceros auklets Cerorhinca monocerata across the North Pacific, we measured inter-annual changes in nutritional stress (as reflected in plasma levels of corticosterone) of adults breeding on 5 colonies (2 and 3 colonies from the western and eastern Pacific, respectively). We also examined concurrent changes in mass and energy content of food loads delivered to chicks. We found that higher summer PDO values were associated with increased corticosterone levels and lower mass and energy contents of the food loads in both the western and eastern North Pacific colonies. Results indicated that oceanographic conditions during higher PDO values induced local changes in forage fish communities, leading to reduced prey availability, which, in turn, increased the nutritional stress of breeding birds. We conclude that the higher summer PDO index in recent years was associated with food-poor conditions for breeding rhinoceros auklets across their reproductive range, and prolonged periods of high summer PDO may be detrimental to the populations of this seabird species. Our results highlight the complexity of the mechanisms of how large-scale climate variability affects seabirds with a large geographical distribution.

Changes in seasonal resource availability and in energetic requirements as offspring grow may force parents to change their trophic ecology throughout the breeding season. Brown skuas Stercorarius antarcticus breed in a highly seasonal environment where the availability of their main food resource changes during the season. We studied the feeding plasticity of breeding brown skuas by assessing their isotopic diet and movement patterns at different stages of their breeding cycle. Blood δ15N values indicated that penguin chicks Pygoscelis spp. and Antarctic krill Euphausia superba constituted most of the diet of brown skuas (up to ~70%), and that there was an increase in the ingestion of lower trophic level prey (most likely Antarctic krill) throughout the breeding period (from 30-46%). This contrasts with movement analysis indicating that 65% of the overall foraging locations were within penguin rookeries. The apparent contradiction between the results from both techniques may be explained by a combination of some skuas feeding mostly at sea or on shore together with secondary ingestion of marine resources from the penguins’ gut by feeding mostly within penguin rookeries. Krill obtained in that way may provide protein to replenish reserves before migration along with globulins through the intake of carotenoids. These results highlight the fact that the trophic ecology of species can be more complex than that suggested by one single method and emphasizes the importance of combining techniques to draw robust conclusions. In addition, our study indicates that skuas may select portions of prey to obtain specific resources to fulfill their nutritional requirements.

Microplastics have been found in all surveyed ecosystems and in the diet of multiple species. Detrimental health impacts of microplastic consumption include reduced growth and fecundity, metabolic stress and immune alterations for both invertebrates and vertebrates. Limited information exists, however, on how disease resistance may be affected by microplastic exposure and consumption. Here, the impact of microplastic (0.01 and 0.05 mg l-1 of polypropylene) on fish host susceptibility to disease and mortality was assessed using the guppy Poecilia reticulata-gyrodactylid Gyrodactylus turnbulli system. Fish exposed to and/or consuming microplastic at both concentrations demonstrated significantly higher pathogen burdens over time compared with fish fed a plastic-free diet. Furthermore, microplastic (at both tested concentrations) was associated with increased mortality events for fish within all treatments, regardless of host infection status. This study adds to the growing body of evidence showing that microplastic pollution can be detrimental to fish welfare by reducing disease resistance.

A coupled physical (Regional Ocean Modeling System, ROMS)-biogeochemical model (N2PZD2) at a horizontal resolution of 3.5 km was implemented for N and NW Iberia, an area of high productivity associated with upwelling. The physical model has been the object of previous studies and has proven its capability to perform well in reproducing the main oceanographic features in the area (upwelling, river plumes, slope currents, fronts, filaments), which is fundamental to properly representing the variability and distribution of the biogeochemical variables. The biogeochemical model was set up to account for the main nutrient inputs in the area: upwelling and rivers. Upwelling input required proper characterization of the nutrient content variability of the Eastern North Atlantic Central Water, which was achieved by using a temperature-nitrate relationship obtained from observations to impose nitrate at the open boundaries. The resulting biophysical model accurately reproduced the timing and interannual variability of the spring bloom compared with satellite chlorophyll (chl a) observations. A comparison with the Instituto Español de Oceanografía’s in situ spring-monitoring Pelacus cruises (which include plankton) revealed that the model was able to reproduce the variability at shorter scales (days) and demonstrated its ability to complement the observational data and reveal the variability in the area around the spring transition. In this respect, both the model and observations showed that productivity on this narrow shelf is affected by seasonal upwelling that results from the interplay of wind, river plumes and light intensity, all varying at interannual, seasonal and event scales.

Small pelagic fish (SPF) play an important ecological role by facilitating energy transfer in marine ecosystems, from lower to higher trophic levels. The Celtic Seas ecoregion is home to several economically important SPF that spend some or all their life in these waters. In recent decades, major changes in the relative abundances of the 6 main SPF in the region (anchovy, herring, horse mackerel, mackerel, sardine, and sprat) have been observed. Changes in the region may impact SPF, and previous studies in neighbouring seas have highlighted possible diet overlap of these species; therefore, it is important to understand the changes in diet overlap and trophic relationships, particularly across different seasons. Consequently, we investigated the seasonal diet composition of these 6 SPF in the Celtic Seas ecoregion, identified diet overlap, and determined species selectivity towards prey size. Combining historical and new observations on fish-stomach contents, diet-overlap indices were computed to quantify potential seasonal intra- and inter-specific overlap. Diet overlaps among species changed between seasons; in particular, sprat and anchovy changed significantly between spring and autumn, and mackerel between spring, summer, and winter. SPF species primarily consumed calanoid copepods, with herring and horse mackerel having more selective diets compared to mackerel, anchovy, and sardine. All species fed at similar trophic levels between seasons. To our knowledge, this study is the first to show seasonal variability in diet overlap among the 6 SPF in the Celtic Seas ecoregion. These results can improve the understanding of feeding dynamics for SPF in ecosystem model outputs.

Habitat heterogeneity is a crucial driver for species distribution across scales. Harbour porpoise Phocoena phocoena basin-wide distribution is linked to prey availability, and small-scale (kilometres to tens of kilometres) differences in distribution are prevalent. However, information on porpoise distribution and foraging-behaviour variations on a micro-scale (~100 m to kilometres) is limited. To monitor harbour porpoise distribution and foraging activity on a micro-scale, we deployed passive acoustic dataloggers, logging porpoise acoustic activity at 6 sites in a small, high porpoise-density area in southern Sweden. Data were collected for almost a year, giving detailed time series on porpoise activity. The time series were analysed using dynamic time warping to compare activity patterns between sites. Large differences were found between sites separated by only a few hundred meters, indicating micro-scale spatial preference. Spectral analysis for temporal cyclicity in activity revealed a dominant peak for 24 h cycles with higher activity at night for all sites. All sites also had a second peak for 29.5 d, linked to the lunar cycle with higher activity during full moon. Activity was overall highest during autumn and winter (September-December). Spatial and temporal patterns were linked to foraging, showing a positive correlation between porpoise presence and the percent of time present with detected foraging. The study demonstrates that harbour porpoise spatial distribution on a micro-scale should be considered in e.g. behavioural, management and conservation studies and actions. In addition, we show that time series statistical methodology is informative and appropriate for analysis of acoustic temporal data.

Large-scale spatial and temporal variability in environmental conditions may result in differences in life-history traits, population demography, and abundance of sandy-beach species. We analyzed the effects of salinity, chlorophyll a (chl a), and sea surface temperature (SST) on population parameters of the wedge clam Donax hanleyanus from 75 South American sandy beaches covering a 15° latitudinal range. Generalized modeling results showed that between-beach differences in abundance, population structure, growth performance, productivity, mortality, and individual shell mass were mainly explained by salinity fluctuations, with chl a and SST as secondary contributors, overriding, in most cases, local habitat features (Dean’s parameter, grain size, slope). Our results provide valuable insights into macroscale ecological processes, setting a basis to delineate conservation guidelines at large spatial scales that respond to the potential effects of climate variability and change on sandy beach populations.

Posidonia oceanica is a dominant marine macrophyte in shallow coastal waters of the Mediterranean and arguably the most important habitat-forming species. While the effects of elevated seawater temperature on P. oceanica have been studied in laboratory experiments and observed in the field following marine heatwaves, it appears that no field surveys to assess long-term influence are available. Making use of the exponential temperature gradient (k = 0.05 m-1) created by thermal effluent from a fossil fuel power station that has been operating for 3 decades, we aimed to fill this knowledge gap by assessing the in situ effects of elevated temperature (ΔT = 0.39°C) on P. oceanica and associated motile macrofauna. Seagrass leaf area and biomass alongside epiphyte biomass rapidly decreased on moving towards the thermal outflow, but no such change was evident for leaf number and shoot density. The observed differences in seagrass shoot attributes may result from differential adaptation of various parts of the plant to thermal stress. Macrofaunal species richness increased on moving towards the effluent source but evenness decreased. These results predict a near-future scenario where even small rises in seawater temperature in the coming decades will impact some attributes of P. oceanica and its epiphytes and cause a shift in the community composition of associated macrofauna towards fewer dominant species.

Determining the relative influence of, and possible synergistic relationships among, environmental and biotic processes on individual growth rates can identify key mechanisms that contribute to variation in body size observed among similar-aged individuals. The timing of ontogenetic shifts in diet or habitat, which themselves can be size-dependent, can have considerable impacts on individual growth trajectories, survival, and year class formation. The southern flounder Paralichthys lethostigma is a coastal flatfish species with juvenile cohorts that occupy diverse estuarine settlement habitats and commonly display 2-3 fold variation in body size by the end of the first growing season. We examined abiotic and biotic factors contributing to differences in early juvenile growth for the 2018 year-class of southern flounder in a North Carolina estuary. Following peak larval settlement (Febuary/March), flounder body sizes began to diverge by April, with differences between settlement habitats contributing to roughly 3-fold variation by August. Stomach content analyses indicated a greater occurrence of fish prey in the diets of southern flounder recovered in mesohaline versus oligohaline settlement habitats. Increased piscivorous foraging in mesohaline habitats was linked to nitrogen (δ15N)-enriched tissues and faster growth rates relative to fish collected in oligohaline habitats. Results from a controlled laboratory experiment provided evidence for the strong effects of diet, with only minor direct effects of salinity on juvenile southern flounder growth. Our findings support the critical role of ontogenetic shifts to piscivorous feeding for growth in young-of-the-year southern flounder and highlights the potential for growth-mortality tradeoffs to exist among estuarine settlement habitats.

Franciscana dolphins in Babitonga Bay represent the only fully estuarine population of this critically endangered species, but this location is also home to a population of Guiana dolphins. Surrounded by large cities and harbors, Babitonga Bay presents intense human activities and potential impacts that may threaten the dolphins. Understanding their habitat use and distribution can inform the implementation of conservation actions and mitigation of such impacts. Here, we used acoustic data from 60 fixed passive acoustic monitoring stations, implemented between June and December 2018. The relationship between the occurrence of franciscanas and environmental variables was investigated with generalized additive mixed models. The selected model presented 51% of explained deviance and included time of day, intensity of presence of Guiana dolphins, maximum slope, and bottom sediment, among other less statistically significant variables. A daily distribution pattern was identified, with franciscanas remaining in the areas of greatest occurrence especially in the morning and seeming to prefer sandy bottom and flatter areas. Areas intensively used by Guiana dolphins were avoided. Additionally, we mapped their distribution using empirical Bayesian kriging to identify the main areas of occurrence and for foraging. Franciscanas are consistently predominant in the innermost region of the estuary, without expressive use of the entrance channel, but with a wider range in winter than in spring. The area around the islands, between the north and south banks, represents an important foraging area, a behavior more frequent during dawn and night. This study provides important insights into critical habitats and behavioral patterns of critically endangered franciscanas in Babitonga Bay.

Two sun coral species, Tubastraea tagusensis and T. coccinea, have successfully colonized reef habitats along the Southwest Atlantic. However, their invasive biology has been largely addressed without considering species-specific distribution patterns. Here, we assessed the distribution and abundance of Tubastraea spp. at vertical rocky reef sites within a number of islands along 120 km of coastline off the northern coast of São Paulo State, Brazil, to (1) investigate possible mechanisms underlying the invasion dynamics in the region, (2) test species-specific distributions according to a key environmental filter (depth), and (3) examine within-patch patterns to assess whether competition, niche-based or neutral processes are best candidates to modulate local species coexistence. Sun corals were found in the great majority of the studied locations, and the probability of finding them at any given reef site was estimated to be 0.54. There was substantial species segregation across locations, consistent with primary priority effects. Within locations, results suggest environmental filtering, with T. coccinea apparently advantaged in more hydrodynamic environments just below the surf zone. At sun coral patches with extensive co-occurrence of T. tagusensis and T. coccinea, the presence of each species can be, remarkably, modeled as an independent event, suggesting neutral coexistence. The spread of sun corals is an ongoing and increasingly invasive process that may be explained by the enemy-release hypothesis and the lack of negative interactions between Tubastraea species. The stochastic nature of small-scale distributions sets an additional challenge to predict (and thus control) sun coral invasion.

Life-history polymorphism in habitat use has been widely reported in aquatic migratory animals. Adult loggerhead sea turtles Caretta caretta in the North Pacific exhibit foraging-habitat polymorphism, showing a 2.4-fold greater reproductive output for neritic foragers than for oceanic ones. However, knowledge of how turtles in each habitat behave and what effect this has on reproduction remains limited. We combined horizontal movement and dive behavior analyses to explore foraging behavior and habitat utilization in adult female loggerheads in the North Pacific. Between 2016 and 2018, satellite relay data loggers were attached to 10 females nesting in Japan. The turtles were tracked for 219.2 ± 185.0 d (±SD) within the range of 10 to 521 d. Three foraging destinations were revealed, with different foraging tactics in each habitat: (1) the neritic East China Sea (ECS), (2) neritic coastal areas of mainland Japan (CMJ), and (3) oceanic North Pacific Ocean (NPO). ECS females mainly foraged on benthic prey with foraging-site fidelity; however, some turtles alternately preyed on benthos and plankton along with their seasonal migration. CMJ females also foraged on benthic prey with site fidelity, whereas NPO females foraged on plankton by drifting eastward with the oceanic currents. Dive-type analyses revealed that the proportion of time spent presumably foraging was similar among the 3 habitats, suggesting that the nutrient richness of prey items and the migration distance between foraging and breeding grounds may cause differences in reproductive outputs among different life-history types of loggerhead turtles.

Hurricanes disturb marine ecosystems by abrupt changes in storm-surge, erosion, freshwater inflow, material loads, or water quality. Hurricane Harvey (25 August 2017) was a Category 4 storm that entered the south Texas, USA, coast and produced a large flood in San Antonio Bay. Benthic abundance, biomass, and diversity have been measured quarterly at 4 stations beginning in 2004. From July to October 2017, macrobenthos decreased to near zero, likely because salinity and dissolved oxygen approached zero. A bivalve mollusk recruitment event began within 8 mo after the storm and continued to July 2018. These short-term responses showed that benthic communities were initially devastated but recovered in less than 1 yr, indicating resilience. However, modeling based on a 13 yr time series yielded the same trend in community metrics, suggesting that benthos would have declined in fall and increased in spring with or without the storm. The long-term results indicate that seasonal dynamics in benthos provide some resistance as well as resilience to storm disturbance. Storms occur at stochastic geological time scales and shape evolutionary history such that they likely do not cause an enduring, devastating disturbance to benthic communities.