Marine Food Webs Research Articles

Advancing the climate-biodiversity-fisheries nexus in the UN Decade of Ocean Science for Sustainable Development

Abstract Climate-driven changes in marine ecosystem structure and function adversely impact the biodiversity and sustainability of living marine resources, food security, and the resilience of coastal communities. Understanding how climate change impacts marine ecosystem biodiversity and global fisheries, i.e. the “climate-biodiversity-fisheries nexus”, is a fundamental element of the UN Decade of Ocean Science for Sustainable Development. Several Ocean Decade-endorsed Programmes within the climate-biodiversity-fisheries nexus are building global networks to transform our capacity to understand, forecast, manage, and adapt to climate-driven changes in ocean ecosystems, including sustaining blue food resources that provide essential food security and nutrition in a rapidly changing world. We compare the scope, objectives, global partnerships, and capacities of these Programmes, facilitating effective collaboration and identifying critical gaps in developing solutions to climate-driven changes in marine food webs, species assemblages, and global fisheries. This work complements the Ocean Decade Vision 2030 process by providing an assessment of actions that are underway and guidance to establish new actions needed to monitor and understand marine biodiversity and manage global fisheries within a changing climate. We provide recommendations for new and existing Ocean Decade Actions around the climate-biodiversity-fisheries nexus to help achieve the Ocean Decade outcomes of a “productive, predicted, healthy, and resilient ocean” by 2030.

Mapping phenoregions and phytoplankton seasonality in Northeast Pacific marine coastal ecosystems via a satellite-based approach

Phytoplankton phenology describes yearly algal growth cycles and characterises the timing, duration, and magnitude of bloom occurrences. This study used satellite chlorophyll-a data from 1998 to 2020 and the Hierarchical Agglomerative Clustering method to define phenoregions based on phytoplankton phenology spatial patterns over the British Columbia and Southeast Alaska coastal oceans. The defined phenoregions were used to simplify the spatial complexity of the heterogenous study region and thus better describe phytoplankton seasonality across the target area. The cluster analysis allowed the delineation of four coherent regions: two coastal regions and northern and southern shelf/offshore regions. Results showed that each phenoregion had distinguishable phytoplankton phenological characteristics, likely due to different physical forcings acting in these areas. Moreover, the interannual variability of the spring bloom initiation was evaluated considering interactions between sea surface temperature (SST) anomalies and the El Niño Southern Oscillation Index (ENSO). Early spring blooms were associated with positive SST anomalies and El Niño conditions; conversely, average or late spring blooms occurred in years with negative SST anomalies and La Niña conditions, with the strongest relationship occurring in the southern shelf/offshore phenoregion. This study provided new insights into the regionalisation of the British Columbia and Southeast Alaska coastal oceans based on phytoplankton phenology patterns. Given the critical role of phytoplankton as the base of the marine food web, such phenoregions have implications for regional zooplankton biomass and fish production. The link between phytoplankton phenology and climate drivers points to the importance of environmental change in phytoplankton bloom dynamics. Further research into the connection between phytoplankton bloom indices and zooplankton community structure and production would be an important step towards using these indices for ecosystem monitoring and fisheries management.

Trophic transfer of dechloranes in marine food webs in Dalian Bay, China

Dechloranes, including dechlorane 602 (Dec 602), dechlorane 603 (Dec 603), dechlorane 604 (Dec 604), dechlorane plus (DP, including syn- and anti-DP) and mirex, were determined in marine food web from Dalian Bay, Northeast China to investigate their occurrence andtrophic transfer. In all organisms, the detection rates were Dec 602 (99%) > mirex (95%) > Dec 603 (92%) > anti-DP (91%) > syn-DP (82%) > Dec 604 (9.6%). The concentrations were 0.92–16 ng/g lipid weight (lw) for mirex, 0.53–2.3 ng/g lw for syn-DP, 1.1–4.5 ng/g lw for anti-DP, 0.19–5.0 ng/g lw for Dec 602, 0.26–1.9 ng/g lw for Dec 603 and 0.020–0.33 ng/g lw for Dec 604. Significant positive relationships (p < 0.0001) were observed between lipid normalized concentrations and trophic levels for mirex (R2 = 0.80) and Dec602 (R2 = 0.82) in food webs, with the calculated TMFs values of 3.09 and 3.39, respectively, indicating the trophic magnification potential of these compounds. For syn-DP, anti-DP, Dec 603 and Dec 604, the similar significant relationships were not found, suggesting that these chemicals do not trophic magnification nor trophic dilution in the food web. With low log KOW values for mirex (7.01) and Dec 602 (8.05), these two compounds have the highest magnifications potentials, while the magnification potential of Dec 603, Dec 604 and DP dramatically decreased because of their extremely big log KOW values (higher than 10). The observed fractional abundance of anti-DP (fanti) ranged of 0.58–0.69, closing to the one in Chinese industrial products, indicating DP isomers had not undergone significant differences of physicochemical or biological process in the studied food web.

The global distribution and climate resilience of marine heterotrophic prokaryotes

Heterotrophic Bacteria and Archaea (prokaryotes) are a major component of marine food webs and global biogeochemical cycles. Yet, there is limited understanding about how prokaryotes vary across global environmental gradients, and how their global abundance and metabolic activity (production and respiration) may be affected by climate change. Using global datasets of prokaryotic abundance, cell carbon and metabolic activity we reveal that mean prokaryotic biomass varies by just under 3-fold across the global surface ocean, while total prokaryotic metabolic activity increases by more than one order of magnitude from polar to tropical coastal and upwelling regions. Under climate change, global prokaryotic biomass in surface waters is projected to decline ~1.5% per °C of warming, while prokaryotic respiration will increase ~3.5% ( ~ 0.85 Pg C yr−1). The rate of prokaryotic biomass decline is one-third that of zooplankton and fish, while the rate of increase in prokaryotic respiration is double. This suggests that future, warmer oceans could be increasingly dominated by prokaryotes, diverting a growing proportion of primary production into microbial food webs and away from higher trophic levels as well as reducing the capacity of the deep ocean to sequester carbon, all else being equal.

Phytoplankton bloom detection and trends in satellite inherent optical properties over the last two decades in a heterogeneous Patagonian coastal system

ABSTRACT To effectively address ecosystem health risks, it is crucial to use detection methods that efficiently cover vast areas with good spatial resolution. These methods should enhance understanding of how phytoplankton blooms might evolve due to climate change. Satellite Ocean Color sensors are advantageous for detecting and monitoring phytoplankton blooms over time. This study uses the Inherent Optical Properties (IOP) index, which considers light absorption by phytoplankton (Ab_phy) and by detritus plus colored dissolved organic matter (Ab_adg), to detect phytoplankton blooms in six subareas within the San Matías Gulf (SMG; Patagonia, Argentina). The findings reveal a significant increase in bloom alerts over the last 20 years in the northwestern and southwestern subareas. Temporal changes in chlorophyll a (Chla) and sea surface temperature (SST) were observed, both showing an increase over the studied period. Environmental features like the diffusive attenuation coefficient (Kd_490) and Ab_phy also showed positive trends in four of the six subareas. The positive trends in SST and Kd_490 suggest a potential reduction in the euphotic zone depth. Additionally, the presence of phytoplankton biomass, indicated by Chla and Ab_phy, is linked to reduced light penetration in the water column due to absorption by the cells and self-shading. A decrease in Ab_adg was observed, while photosynthetically active radiation (PAR) showed no significant trend over the last two decades. These patterns could significantly impact the frequency and timing of phytoplankton blooms, altering their community composition and phenology. Such changes have profound implications for the entire marine food web and the ecosystem services within the SMG. The results underscore the importance of incorporating optical data for monitoring phytoplankton blooms across multiple areas.

Path analysis reveals combined winter climate and pollution effects on the survival of a marine top predator.

Marine ecosystems are experiencing growing pressure from multiple threats caused by human activities, with far-reaching consequences for marine food webs. Determining the effects of multiple stressors is complex, in part, as they can affect different aspects of biological organisation (behaviour, individual traits and demographic rates). Determining the combined effects of stressors, through different biological pathways, is key to predict the consequences for the viability of populations threatened by global change. Due to their position in the food chain, top predators such as seabirds are considered more sensitive to environmental changes. Climate change is affecting the prey resources available for seabirds, through bottom-up effects, while organic pollutants can bioaccumulate in food chains with the greatest impacts on top predators. However, knowledge of their combined effects on population dynamics is scarce. Using a path analysis, we quantify the effects of climate change and pollution on the survival of adult great black-backed gulls, both directly and through effects of individuals' body mass. Warmer ocean temperatures in gulls' winter foraging areas in the North Sea were correlated with higher survival, potentially explained by shifts in prey availability associated with global climate change. We also found support for indirect negative effects of organochlorines, highly toxic pollutants to seabirds, on survival, which acted, in part, through a negative effect on body mass. The results from this path analysis highlight how, even for such long-lived species where variance in survival tends to be limited, two stressors still have had a marked influence on adult survival and illustrate the potential of path models to improve predictions of population variability under multiple stressors.

Diatom abundance in the polar oceans is predicted by genome size.

A principal goal in ecology is to identify the determinants of species abundances in nature. Body size has emerged as a fundamental and repeatable predictor of abundance, with smaller organisms occurring in greater numbers than larger ones. A biogeographic component, known as Bergmann's rule, describes the preponderance, across taxonomic groups, of larger-bodied organisms in colder areas. Although undeniably important, the extent to which body size is the key trait underlying these patterns is unclear. We explored these questions in diatoms, unicellular algae of global importance for their roles in carbon fixation and energy flow through marine food webs. Using a phylogenomic dataset from a single lineage with worldwide distribution, we found that body size (cell volume) was strongly correlated with genome size, which varied by 50-fold across species and was driven by differences in the amount of repetitive DNA. However, directional models identified temperature and genome size, not cell size, as having the greatest influence on maximum population growth rate. A global metabarcoding dataset further identified genome size as a strong predictor of species abundance in the ocean, but only in colder regions at high and low latitudes where diatoms with large genomes dominated, a pattern consistent with Bergmann's rule. Although species abundances are shaped by myriad interacting abiotic and biotic factors, genome size alone was a remarkably strong predictor of abundance. Taken together, these results highlight the cascading cellular and ecological consequences of macroevolutionary changes in an emergent trait, genome size, one of the most fundamental and irreducible properties of an organism.

Coccolithophore Assemblage Response to Indian Monsoon–ENSO Teleconnections During the Last Century

AbstractWe present a new, annually resolved coccolithophore relative abundance record (1889–1993 CE) from a laminated marine sediment core obtained from the northeastern Arabian Sea to document assemblage variations during the last century. Our analysis revealed that ∼80% of the assemblage is composed of the coccolithophore species Gephyrocapsa oceanica, Emiliania huxleyi, and Florisphaera profunda. Hierarchical clustering of the coccolithophore data delineates time intervals (1889–1909 CE, 1910–1959 CE, 1960–1993 CE) comparable to previously reported interdecadal changes of the El Niño–Southern Oscillation (ENSO)–Indian monsoon variance. We find that F. profunda (Fp%) is positively correlated with central Pacific ENSO (Niño 4 and Niño 3.4). Frequency analyses of Fp% match ENSO quasiperiodicity reported from instrumental data and proxy records and support the existence of previously described ENSO–Indian monsoon teleconnections. Furthermore, the increased variance of Fp% and associated decrease in marine primary productivity starting ∼1960 CE appears to be driven by decreased upward nutrient transport linked to increased surface water stratification due to surface ocean warming. With the predicted increases in frequency and strength of central Pacific El Niño as well as surface ocean warming and upper ocean stratification in the Indian Ocean over the coming century, our results imply further impacts on coccolithophores in the northeastern Arabian Sea that may have cascading effects on the marine food web and global biogeochemical cycles.

Impacts of the Early Eocene Climatic Optimum (EECO, ∼53‐49 Ma) on Planktic Foraminiferal Resilience

Plain Language SummaryThe Early Eocene Climatic Optimum (EECO) is an interval of prolonged warmth that occurred ∼53 to 49 million years ago. Planktic foraminifera are important (alongside coccolithophores) for understanding the carbon cycle and determining export production in the ocean. To understand how foraminifera can be impacted by extreme heat, we analyzed samples from the Pacific Ocean through measuring changes in (a) the relative abundance, that is, the count of different taxa in a sample, and (b) body (shell) size of planktic foraminifera. At the start of the EECO, the abundance of the genera Morozovella and Chiloguembelina decreased. Despite this decline, the number of foraminifera being buried and the size of the largest shells in a sample does not change. We attribute this to the increased abundance of the genus Acarinina. In general, the accumulation of foraminifera remains stable while the relative abundance of foraminifera to coccolithophores decreases. Together, this implies that coccolithophores are increasing in abundance, and/or mass. During the EECO, one group of foraminifera was able to counterbalance the decrease in abundance of other genera. This highlights the resilience of open‐ocean carbonate production and the base of the marine food web.

An Investigation on the Presence and Risk Assessment of Microplastics in Quilon Beach, South West Coast of India

Microplastics (MPs) are the most serious emerging pollutant around the globe. Anthropogenic activities are the major contributor of MPs in beach sediments. MPs are widely distributed along beaches and pose a serious threat to the marine food chain including human health. The present study aims to investigate, for the first time, the occurrence, quantification of abundance and risk assessment of MPs in Quilon beach, India and also identifies the potential sources along with the assessment of degree of MPs contamination using Pollution load index (PLI) and Pollution Hazard index (PHI) parameters. Sampling was conducted in dry season in the beach. A total of thirty-three samples were collected establishing a 20m grid pattern along the study area. MPs of size range 5mm - < 0.25mm were considered. The average abundance of MPs in the study area is 3145±2515 MPs/kg of sand. Polyester (PES), Acrylonitrile butadiene styrene (ABS) are the major polymer types in the study area. Fibre was the most dominant shapes. The frequent colours found were white and transparent. MPs of size <0.25mm were the most common of all the samples. Anthropogenic activities including sewage effluents, fishing and tourism activities might be the main sources of MPs pollution in this area.

Seasonal dynamics of polycyclic aromatic hydrocarbons in microplankton from Kaohsiung Harbor (Taiwan Strait, northeastern South China Sea)

The impact of polycyclic aromatic hydrocarbons (PAHs) on the marine food web is crucially understudied in the primary trophic system. We evaluated the seasonal dynamics of PAHs in microplankton in a polluted environment (Taiwan), northeastern South China Sea. Replicate size-fractionated microplankton (55–1000 μm) were freeze-dried, and PAHs were extracted with a 1:1 v/v ratio of acetone: n-hexane, then analyzed using GC–MS. Total PAHs ranged between 68 and 2548 ng/g dw in microplankton, greatest during spring (130–2548 ng/g), followed by autumn (135–772 ng/g) and summer (44–423 ng/g). Spatial distribution varied through seasons but was higher in the southern part (S6 > S4 > S5 > S2 > S3 > S1 > S7), dominated by higher-ring PAHs from mixed pyrogenic and petrogenic sources. PAHs are significantly correlated with environmental factors, especially in colder seasons and lower salinity areas. Suspended matter and plankton influenced PAH transport and partitioning seasonally. Plankton's PAHs seasonal changes and environmental influences are revealed in an anthropic environment.

Small pelagic fish in the shallow Wadden Sea show opportunistic feeding with a strong benthic link

Abstract Small pelagic fish (SPF) are crucial in marine food webs, transferring energy from plankton to higher trophic levels. This study focuses on herring (Clupea harengus) and sprat (Sprattus sprattus), addressing knowledge gaps in their feeding ecology in a nursery area, the Dutch Wadden Sea. We conducted a year-long, monthly survey, and used DNA metabarcoding to analyse zooplankton samples and stomach contents of two size classes of herring and sprat. Intra-, interspecific, and seasonal variations in fish condition, stomach fullness, and diet composition, along with selective feeding, were studied. Our study showed that condition and diet composition of herring and sprat, along with zooplankton density, exhibited a clear seasonal pattern. Juvenile herring and sprat displayed opportunistic feeding behaviour, rather than showing distinct prey selection. Besides copepods, we regularly observed (larvae of) benthic invertebrates in their diet. This emphasizes the crucial role of SPF as energy transfer agents, not solely between trophic levels, but also from benthic to pelagic habitats. Furthermore, fish post-larvae were part of the diet of larger herring (10–15 cm). Because of its unprecedented temporal and taxonomical detail, this study advances the understanding of seasonal dynamics of dominant components at the base of the Wadden Sea food web.

Anthropogenic particles determination in northern krill (Meganyctiphanes norvegica) from the Azores region: A keystone species for marine food webs

Plastic pollution poses a significant threat to marine ecosystems. Microfibres from fabrics have become the most prevalent shape of microplastic found in the marine environment. The northern krill (Meganyctiphanes norvegica) is the most abundant euphausiid species in the northern hemisphere, playing a crucial role in various pelagic ecosystems. Anthropogenic microparticles in northern krill was assessed for the first time in samples collected in the Azores on two occasions - April 2019 (n = 480) and April 2023 (n = 480). Analysis of all individuals revealed 533 anthropogenic particles, with an average abundance of 0.56 ± 0.14 items per individual and, no significant differences between years. Microfibres were the most common shape (94.8 %), with the remaining items being fragments (5.2 %), and blue and black were the predominant colours. MicroFourier transform infrared spectroscopy analysis (μFTIR) of 22.1 % of the total number of particles, showed that they were mainly cellulosic (65.3 %) - either natural or semisynthetic - followed by polyester (7.6 %). Our finding of microplastics in the northern krill raises important questions due to its crucial role in marine food webs. The intake of anthropogenic particles, particularly those that are 100 % synthetic, suggests that the northern krill may act as a transfer vector of these pollutants to higher trophic levels.

Accumulation of Per- and Polyfluoroalkyl Substances (PFAS) in Coastal Sharks from Contrasting Marine Environments: The New York Bight and The Bahamas.

Per- and polyfluoroalkyl substances (PFAS) enter the marine food web, accumulate in organisms, and potentially have adverse effects on predators and consumers of seafood. However, evaluations of PFAS in meso-to-apex predators, like sharks, are scarce. This study investigated PFAS occurrence in five shark species from two marine ecosystems with contrasting relative human population densities, the New York Bight (NYB) and the coastal waters of The Bahamas archipelago. The total detected PFAS (∑PFAS) concentrations in muscle tissue ranged from 1.10 to 58.5 ng g-1 wet weight, and perfluorocarboxylic acids (PFCAs) were dominant. Fewer PFAS were detected in Caribbean reef sharks (Carcharhinus perezi) from The Bahamas, and concentrations of those detected were, on average, ∼79% lower than in the NYB sharks. In the NYB, ∑PFAS concentrations followed: common thresher (Alopias vulpinus) > shortfin mako (Isurus oxyrinchus) > sandbar (Carcharhinus plumbeus) > smooth dogfish (Mustelus canis). PFAS precursors/intermediates, such as 2H,2H,3H,3H-perfluorodecanoic acid and perfluorooctanesulfonamide, were only detected in the NYB sharks, suggesting higher ambient concentrations and diversity of PFAS sources in this region. Ultralong-chain PFAS (C ≥ 10) were positively correlated with nitrogen isotope values (δ15N) and total mercury in some species. Our results provide some of the first baseline information on PFAS concentrations in shark species from the northwest Atlantic Ocean, and correlations between PFAS, stable isotopes, and mercury further contextualize the drivers of PFAS occurrence.

Omega-3 fatty acids-critical for the marine food web and for seabird productivity

Abstract Seabird reproductive success in northern latitudes is often linked with prey abundance, availability, size, or species. Causes are often broadly explained as changes in ocean currents/temperatures, or diets. Few studies trace diets down the food web to primary producers, thus missing what I propose as an underlying cause of seabird colony failure, dietary abundance of essential omega-3 polyunsaturated fatty acids (PUFA). PUFA differ from other nutrients because they are, in part, ligands—critical for reproduction and other physiological processes for the entire marine food web, not just for seabirds. Diatoms are one of the few life forms that can produce PUFA de novo, and a lack of PUFA in zooplankton and fish reduces their abundance and productivity, with consequences up the food web. Since the mid-1980s, historical prey of breeding seabirds has decreased, and frequency of colony failures has increased. In years of failure, prey often had less fat than historically preferred species. Likewise, proportions of alternate species’ PUFA, from published papers, show lower values than in historical prey. Production of PUFA by diatoms is depressed in warmer and more acidic environments, and I hypothesize that these warmer and more acidic seas have affected production of PUFA over the past 3–4 decades. Assuming this is true, I propose that these lower amounts of PUFA have negatively impacted the breeding success of all members of the marine food web, not just seabirds.

Erosion of fish trophic position: an indirect effect of fishing on food webs elucidated by stable isotopes.

Fishing has significant trophodynamic impacts on marine communities, including reductions in the mean trophic position (TP) of the ecosystem resulting from a decrease in the abundance and size of species and individuals with high TPs. This study demonstrates the erosion of fish TP, an additional process that results in lower TP of individuals of a given size, which may exacerbate the effects of fishing on the food web. A stable isotope approach based on the tRophicPosition Bayesian method was used to quantify the TP of 12 target marine species at a given length, and compare their TP between fishery-restricted areas and trawled areas. The results show a difference in the TP of six benthic and apical nekto-benthic predators, which feed in the median at about 0.5 TP lower in trawled areas. It appears that current 'fishing down marine food webs' analyses may underestimate the trophic effects of fishing. Accounting for changes in trophodynamics of individuals at a given size is important to detect indirect effects through food web interactions. The application of a trawling ban may lead to the restoration of lost trophic structure; however, trophic changes may occur more slowly than changes in biomass. This article is part of the theme issue 'Connected interactions: enriching food web research by spatial and social interactions'.

Usage of Diadema setosum as a bioindicator of microplastic pollution in fishing barns

This study is undertaken to evaluate potential risk of microplastic contamination in a fishing barn by using Diadema setosum as a bioindicator. Microplastic (MP) pollution levels and their potential impacts on marine biota are still unknown compared to coastal and offshore environments. For this purpose, 19 individuals of D. setosum were collected and microplastic abundance in the gastrointestinal tract (GIT) and gonad were investigated. Mean microplastic abundance in GIT was found as 3.0 MPs±3.1 MPs per individual and 0.9±1.0 MPs per g wet weight. Mean microplastic abundance in the gonad was found as 0.3±0.6 MPs per individual and 0.08±0.2 MPs per g wet weight. Among all MPs, 45% of extracted MPs were fiber and followed by fragment (44%) and pellet (11%). Regarding size, majority of the MPs extracted from GIT and all of the MPs extracted from gonad were small size MPs (less than 1 mm in size). FTIR analysis validated the plastic nature of suspected particles and polyethylene (PE) (50%) and polypropylene (PP) (50%) were found as the common type of polymers. These polymers are main polymers used in the production of fishing nets; therefore, this result seems to validate the anthropogenic influence in the study area. This study contributes to the knowledge of the transfer of microplastics to the marine food web and highlights the need for protective measurements.

Spatial food webs in the Barents Sea: atlantification and the reorganization of the trophic structure.

Climate change affects ecosystems at several levels: by altering the spatial distribution of individual species, by locally rewiring interspecific interactions, and by reorganizing trophic networks at larger scales. The dynamics of marine food webs are becoming more and more sensitive to spatial processes and connections in the seascape. As a case study, we study the atlantification of the Barents Sea: we compare spatio-temporal subsystems at three levels: the identity of key organisms, critically important interactions and the entire food web. Network analysis offers quantitative measurements, including centrality indices, trophic similarity indices, a topological measure of interaction asymmetry and network-level measures. We found that atlantification alters the identity of key species (boreal demersals becoming hubs), results in strongly asymmetric interactions (dominated by haddock), changes the dominant regulation regime (from bottom-up to wasp-waist control) and makes the food web less modular. Since the results of food web analysis may be quite sensitive to network construction, the aggregation of food web data was explicitly studied to increase the robustness of food web analysis. We found that an alternative, mathematical aggregation algorithm better preserves some network properties (e.g. density) of the original, unaggregated network than the biologically inspired aggregation into functional groups. This article is part of the theme issue 'Connected interactions: enriching food web research by spatial and social interactions'.

Physiological responses of the microalga Isochrysis galbana exposed to polystyrene microplastics with different particle sizes

Due to continuous increase in marine plastic waste, microplastics are ubiquitous in the marine environment. However, there are few studies on the harmful effects caused by microplastics with different particle sizes, and the interaction between particle size and concentration requires further investigation. This study explored the differences in physiological and biochemical responses, photosynthesis and oxidative stress damage of the microalga Isochrysis galbana exposed to three different particle size microplastics. It was found that different particle sizes and concentrations of microplastics resulted in significant differences (p < 0.05) in the growth rate, photosynthesis, and oxidative stress level of I. galbana. With the decrease of the particle size and lowering concentration of microplastics, the growth rate, photosynthesis and oxidative stress levels of I. galbana were reduced. Significant differences in photosynthesis and oxidative stress levels were observed when I. galbana was exposed to smallest particle size and lowest concentration of microplastics. This study provides new insights about whether polystyrene microplastics of different particle sizes and concentrations exhibit complex effects on microalgae, and explores the underlying reasons for such effects. In short, this study predicts the exacerbating adverse effects of microplastic pollution on the primary productivity, with significant implications for marine food webs and ecosystem health.

Feeding Habits and Prey Composition of Six Mesopelagic Fish Species from an Isolated Central Mediterranean Basin

Mesopelagic fishes hold an important position in marine food webs, serving as a link between lower trophic levels and top predators and transferring energy from their deep mesopelagic habitat to shallower oceanic layers. Despite their ecological importance, research on mesopelagic fishes’ diet and feeding habits in the Mediterranean Sea is far from thorough. The present work attempts to assess the preying patterns and diet composition of four myctophid (Benthosema glaciale, Ceratoscopelus maderensis, Myctophum punctatum, Notoscopelus elongatus) and two sternoptychid (Argyropelecus hemigymnus, Maurolicus muelleri) species from the Corinthian Gulf (Ionian Sea, Greece), sampled during pelagic trawl surveys in 2018 and 2019. Stomach vacuity was high for myctophids caught during daytime, a pattern which sternoptychids did not follow. Estimated trophic indices revealed high dietary diversity (Shannon’s H’ index) for most investigated species, but a narrow trophic niche breadth (Levins’ normalized Bn index). Copepods and various marine crustaceans were dominant in all diets, classifying them under the zooplanktivorous trophic guild, while A. hemigymnus exhibited high concentrations of particulate organic matter in their stomachs and N. elongatus exhibited consumption of fish. Diet overlap was significant among most studied mesopelagic species, as indicated by Shoener’s S index and confirmed by both the multidimensional scaling ordination and a hierarchical cluster analysis. Information on mesopelagic fishes’ diet composition in this poorly studied part of the Mediterranean is useful in further assessing and parameterizing marine food webs and midwater trophic interactions, as well as in quantifying the ensued energy transfer to top predators of commercial interest or conservation concerns.