Functioning Of Marine Ecosystems Research Articles

Temporal and spatial variability in the feeding behavior of the black sea urchin Arbacia lixula (Echinodermata: Echinoidea) from the north-western Algerian coast

The black sea urchin Arbacia lixula (Linnaeus, 1758) is one of the most domi-nant echinoids in the sublittoral communities of the Mediterranean Sea, where it is considered an essential structuring species by its grazing activity. The present work is considered to be the first study to address the diet of the species A. lixula in Algeria. This study aims to perform on the one hand; a temporal monitoring of the food preferences of two populations of A. lixula living in two different sites in shallow water (port of Salamandre, Stidia) on the coast of Mostaganem (Algeria) during the years 2015 and 2016, and on the other hand; get an idea of the variations of the different trophic sources used and appreciated by this echinoid. The quantitative and qualitative aspect is achieved by monitoring the evolution of the repletion index as well as the identification of the items present in the digestive contents by the contact method of Jones (1968). The results of this monitoring showed that it is an opportunistic species which adapts its diet according to the quality and quantity of food available. Arbacia lixula prefers encrusted coralline algae with a large faunal fraction. In areas rich in nutrients, the spines of these sea urchins may elongate to half the diameter of the test. Based on the results, A. lixula can be associated with habitat, seasonal changes or other specific environmental parameters that merit further development in order to fully understand its functioning in marine ecosystems.

The Influence of pCO2-Driven Ocean Acidification on Open Ocean Bacterial Communities during A Short-Term Microcosm Experiment in the Eastern Tropical South Pacific (ETSP) off Northern Chile.

Due to the increasing anthropogenic CO2 emissions, Ocean Acidification (OA) is progressing rapidly around the world. Despite the major role that microorganisms play on the marine biogeochemical cycling and ecosystem functioning, the response of bacterial communities upon OA scenarios is still not well understood. Here, we have conducted a detailed characterization of the composition and relative abundance of bacterial communities in the water column of an open-ocean station in the Eastern Tropical South Pacific (ETSP) off northern Chile and their interactions with environmental factors. In addition, through a short-term microcosm experiment, we have assessed the effect of low pH/high pCO2 conditions over the abundance and genetic diversity of bacterial communities. Our results evidence a clear partitioning of community composition that could be attributed mostly to dissolved oxygen. However, our experimental approach demonstrated that low pH/high pCO2 conditions might modify the structure of the bacterial community, evidencing that small changes in pH may impact significantly the abundance and diversity of key microorganisms. This study constitutes a first step aiming to provide insight about the influence of changing carbonate chemistry conditions on natural bacterial communities and to shed light on the potential impact of OA in biogeochemical cycles on the ETSP region.

Main drivers of spatial change in the biomass of commercial species between summer and winter in the NW Mediterranean Sea

There is a general lack of information related to the spatial structure and functioning of marine ecosystems considering seasonality. Here, we modeled the biomass distribution of eight commercial marine species in the northwestern Mediterranean Sea during winter and summer. We hypothesised that the seasonal differences of the water column and the spatial heterogeneity of oceanographic conditions in the study area could result in seasonal variations on the species biomass distributions. We employed a Bayesian hierarchical species distribution modelling approach (B-SDM) with data from two experimental trawl surveys to analyse which are the significant drivers in each season. Our results showed that bathymetry, temperature and fishing patterns are important variables explaining the species spatial biomass distributions. Furthermore, we found seasonal differentiation in the spatial distribution of biomass for all the studied species. Our results provide essential knowledge about the seasonal distributions of key species in the Mediterranean Sea, with important management implications.

A Growing Freshwater Lens in the Arctic Ocean With Sustained Climate Warming Disrupts Marine Ecosystem Function

AbstractOne of the most robust changes in the hydrological cycle predicted by Earth System Models (ESMs) during the remainder of 21st century is an increase in the difference between precipitation and evapotranspiration (P‐E) in arctic and boreal regions. We explore the long‐term consequences of this change for marine ecosystems in the Arctic Ocean using the Community Earth System Model forced with a business as usual scenario of future greenhouse gas concentrations. We find that by the year 2300 increases in freshwater delivery considerably reduce Arctic Ocean surface salinity, creating a freshwater lens that has far‐reaching impacts on marine biogeochemistry. The expanding freshwater lens limits vertical nutrient supply into the euphotic zone by enhancing vertical stratification and accelerating surface lateral mixing with surface waters in the North Atlantic, which become increasingly nutrient depleted from weakening of the Atlantic Meridional Overturning Circulation (AMOC). The resulting increase in nutrient stress reduces marine export production in the Arctic Ocean by 53% in 2300 relative to the 1990s and triggers a shift in community composition with small phytoplankton replacing diatoms. At the same time, the seasonal timing of export production undergoes a 2‐month forward shift, with the peak advancing from July to May. This suggests that the threat to food webs and higher trophic levels may intensify after the year 2100 as gains in productivity from sea ice loss saturate and freshwater impacts on nutrient stress continue to strengthen. Our analysis highlights the critical importance of changing terrestrial hydrology and land‐ocean coupling as drivers of long‐term biogeochemical change in the Arctic Ocean and the necessity of multi‐century climate change projections.

Zooplankton functional group responses to environmental drivers off the west coast of Vancouver Island, Canada

Zooplankton diversity and biomass are integral to marine ecosystem functioning. Functional trait-based approaches enable an examination of ecosystem dynamics in which species groups are defined by their functional roles (i.e. functional groups) within the ecosystem, rather their taxonomic identity. Changes in the relative and absolute biomass of zooplankton functional groups may affect the productivity of higher trophic levels via change in secondary production rates and the efficiency of energy transfer. Traits from 55 mesozooplankton species were assembled from the literature and applied to a 35-year time series (1980–2016) for the southern shelf area off the west coast of Vancouver Island, Canada. Eight functional groups were identified by clustering species on the basis of functional trait similarity. A time series of biomass anomalies was calculated for each functional group, after which links between functional group biomass anomalies and several environmental variables were examined. Generalized additive modeling (GAM) identified local sea surface temperature as the most important driver of biomass anomaly patterns for three groups: Doliolids, Omnivore-Herbivores, and the Active Ambush Omnivores. The Southern Oscillation Index (SOI) was also a main driver for three groups: Egg-Brooding Carnivores, Broadcast Carnivores, and Cruise Carnivores-A. The Ocean Niño Index (ONI) was significant for Active Ambush Omnivores and Egg-Brooding Carnivores, whereas the Pacific Decadal Oscillation (PDO) was a driver of Broadcast Carnivores and Cruise Carnivores-A. The Doliolids group also varied with surface salinity, and Cruise Carnivores-B with the North Pacific Gyre Oscillation (NPGO). The relative contribution of several zooplankton functional groups to the overall biomass showed no temporal trends but some groups had increased or decreased abundance contributions. This suggests functional redundancy within groups, as smaller or larger species may dominate based on environmental conditions. Our analysis demonstrates that functional group biomass anomalies vary with environmental variables, where conditions may favor certain functional groups, therefore dictating how the ecosystem is functioning.

Seasonal Variations of Picoeukaryote Community Structure in Zhoushan Fishing Ground, East China Sea

Picoeukaryotes (<2–3 µm) are major oceanic primary producers and play a crucial role for the functioning of marine ecosystems. However, the community structure of such communities remains poorly understood, especially in the East China Sea (ECS). We investigated the seasonal variations of abundance and diversity of picoeukaryotes, and recorded environmental variables, along a transect in Zhoushan Fishing Ground. High-throughput sequencing was used for sequencing the V4–V5 variable region within the 18S rRNA gene to analyze genetic diversity and relative abundance of picoeukaryotes. A total of 40 phyla, 68 classes, 99 orders, 126 families, and 140 genera were observed. The estimated richness and diversity indices were both higher in each season. The composition and dominant picoeukaryotes changed significantly at the class level with the seasons alternating. Basidiomycota, Ciliophora, Ascomycota and Cryptomonadales were observed throughout the year. The Linear Discriminant Analysis (LDA) revealed the predominant discriminant taxa of four seasonal groups. Redundancy analysis (RDA) showed that NO2− and salinity played very important roles to picoeukaryotes for all the spring samples and DS5 sample in winter, PO43− and pH affected mostly picoeukaryotes for winter samples and autumn samples.

Plankton net mesh size influences the resultant diversity and abundance estimates of copepods in tropical oligotrophic ecosystems

Quantitative assessment of planktonic organisms is a key issue in understanding biodiversity, biomass, and carbon fluxes in marine ecosystems during the ongoing Anthropocene. However, the implications of the choice of plankton sampling equipment in tropical marine ecosystems have not been fully addressed. The goal of this study was to investigate the abundance and diversity of copepods derived from two different mesh sizes, 120 and 300 μm, to determine differences that may change our perception of the actual role of the key planktonic organisms in tropical marine ecosystems, due to the fact that missing information may be a real problem in trophic estimations (e.g. benthic-pelagic coupling processes in coastal areas). Samples were collected along 650 km of coastline in the Equatorial Atlantic. The average abundance of copepods calculated using the 120 μm net was five times higher than that of the 300 μm net. However, species richness was higher when using the 300 μm net compared to that of the 120 μm. Using the 300 μm net, the number of exclusive taxa (not found in the 120 μm mesh sampling) was higher. The Venn diagram showed that 10% of the copepod taxa were recorded exclusively in 120 μm net, whereas only 30% occurred in the 300 μm net. To improve our understanding of the structure and functioning of tropical marine ecosystems, plankton nets with smaller mesh openings should always be used to estimate abundance because of the dominance of small organisms in the nutrient-poor food webs, giving a new perspective on the available energy in water column and benthic processes of suspension feeding organisms. The absence of these smaller nets will produce an inaccurate picture of the plankton communities and their contributions to other trophic levels, including the blue carbon budget estimates worldwide.

Contrasting Futures for Australia’s Fisheries Stocks Under IPCC RCP8.5 Emissions – A Multi-Ecosystem Model Approach

Climate-driven trends in ocean temperature and primary productivity are projected to differ greatly across the globe, triggering variable levels of concern for marine biota and ecosystems. Quantifying these changes, and the complex ways in which resource-dependent communities will need to respond, is inherently difficult. Existing uncertainty about the structure, function and responses of marine ecosystems, means that a multi-model or ensemble model approach is the most prudent means of assessing the potential ecosystem responses to climate change. In this study, climate-ecological projections of 13 marine ecosystem models for regions around Australia were evaluated. Model types included dynamic food web, spatial whole of ecosystem, intermediate complexity, species distribution, and size spectrum models and were all forced by high-resolution ocean model data. Each Australian region and fishery will face its own challenges in terms of ecosystem shifts and fisheries management responses over the next 30 years. Across regions, demersal systems appear to be more strongly affected by climate change than pelagic systems, with invertebrate species in shallow waters likely to respond first and to a larger degree. With the assistance of qualitative confidence evaluations, the multi-model approach was useful for identifying the likely state of concern for each functional group and thus adaptive management and research priorities. Largest model discrepancies were found between the regional ecosystem models that represent trophic interactions and the species distribution models, with implications for future assessments and adaption planning. Study results highlight that fisheries and their management will need to foster pro-active and flexible adaptation options to make the most of coming opportunities and to minimize risks or negative outcomes.

Enabling conditions for community-based comanagement of marine protected areas in the United States

Comanagement is recognized, practiced, and recommended as an effective, equitable approach to place-based protection of marine resources. Despite acknowledged benefits and its potential for improved management outcomes, in the U.S., comanagement of marine protected areas (MPAs) is a relatively new approach, with limited applications. This paper reveals social, ecological and institutional conditions that enabled, or hindered, development of comanagement as an outcome of collaborative processes undertaken by community-based actors and state-based resource managers in three U.S. MPA case studies. A mixed method design, consisting of a literature review, in-depth interviews and document analysis was used to analyze MPAs in Hawai‘i, California and Florida where: (1) comanagement systems have developed between state government and community-based partners, (2) protected area boundaries and objectives are clearly defined, and, (3) marine habitat protection is a primary management objective. Eight enabling conditions were present in all three cases. Four of these conditions were consistent with preconditions identified in a published conceptual framework for comanagement arrangements synthesized from the literature and direct observations – an opportunity for negotiation, a legally mandated or brokered incentive, a willingness by local users to contribute, and leadership. Four more enabling conditions emerged from this study – connection to place, a capacity crisis, government willingness to partner, and a clear and just process. As managers strive to protect marine ecosystem function in the face of chronic environmental stressors and limited government support for environmental protection, applying these findings to leverage conditions that enable comanagement can help build community-based capacity to effectively manage MPAs.

Remnant kelp bed refugia and future phase-shifts under ocean acidification.

Ocean warming, ocean acidification and overfishing are major threats to the structure and function of marine ecosystems. Driven by increasing anthropogenic emissions of CO2, ocean warming is leading to global redistribution of marine biota and altered ecosystem dynamics, while ocean acidification threatens the ability of calcifying marine organisms to form skeletons due to decline in saturation state of carbonate Ω and pH. In Tasmania, the interaction between overfishing of sea urchin predators and rapid ocean warming has caused a phase-shift from productive kelp beds to overgrazed sea urchin barren grounds, however potential impacts of ocean acidification on this system have not been considered despite this threat for marine ecosystems globally. Here we use automated loggers and point measures of pH, spanning kelp beds and barren grounds, to reveal that kelp beds have the capacity to locally ameliorate effects of ocean acidification, via photosynthetic drawdown of CO2, compared to unvegetated barren grounds. Based on meta-analysis of anticipated declines in physiological performance of grazing urchins to decreasing pH and assumptions of nil adaptation, future projection of OA across kelp-barrens transition zones reveals that kelp beds could act as important pH refugia, with urchins potentially becoming increasingly challenged at distances >40 m from kelp beds. Using spatially explicit simulation of physicochemical feedbacks between grazing urchins and their kelp prey, we show a stable mosaicked expression of kelp patches to emerge on barren grounds. Depending on the adaptative capacity of sea urchins, future declines in pH appear poised to further alter phase-shift dynamics for reef communities; thus, assessing change in spatial-patterning of reef-scapes may indicate cascading ecological impacts of ocean acidification.

Trophic structure of southern marine ecosystems: a comparative isotopic analysis from the Beagle Channel to the oceanic Burdwood Bank area under a wasp-waist assumption

Understanding the structure and functioning of marine ecosystems has become a critical issue to assess the potential short- and long-term effects of natural and anthropogenic impacts and to determine the knowledge needed to conduct appropriate conservation actions. This goal can be achieved in part by acquiring more detailed food web information and evaluating the processes that shape food web structure and dynamics. Our main objective was to identify large-scale patterns in the organization of pelagic food webs that can be linked to a wasp-waist (WW) structure, proposed for the southwestern South Atlantic Ocean. We evaluated 3 sub-Antarctic marine areas in a regional context: the Beagle Channel (BC), the Atlantic coast of Tierra del Fuego (CA) and the oceanic Burdwood Bank area (BB). We used carbon and nitrogen isotopic information of all functional trophic groups, ranging from primary producers to top predators, and analyzed them through stable isotope-based Bayesian analyses. We found that BC and BB have a more pronounced WWstructure compared to CA. We identified species at mid to low trophic positions that play a key role in the trophodynamics of each marine area (e.g. Fuegian spratSprattus fuegensis, longtail southern codPatagonotothen ramsayiand squat lobsterMunida gregaria) and considered them as the most plausible WW species. The identification of the most influential species within food webs has become a crucial task for conservation purposes in local and regional contexts to maintain ecosystem integrity and the supply of ecosystem services for the southwestern South Atlantic Ocean.

Spatiotemporal Patterns in Diversity and Assembly Process of Marine Protist Communities of the Changjiang (Yangtze River) Plume and Its Adjacent Waters.

Marine protists are highly heterogeneous and play key roles in the structure and functioning of marine ecosystems. However, little is known on the underlying biogeographic processes and seasonal diversity patterns that shape their community assembly in a regional scale in marginal sea. In this study, we conducted high-throughput sequencing of 18S rRNA gene to survey the protist community compositions (PCCs) of the Changjiang (Yangtze River) plume, an intensely human-affected coastal area, to the adjacent continental shelf waters over three seasons. Furthermore, the different impacts of environmental and spatial factors on marine PCCs were examined. The results revealed significant dissimilarities of PCC’s diversity among seasons and habitats, with more obvious seasonal variations in the Changjiang plume. Procrustes analysis showed better consistency of the community-environment relationship in shelf area, further supported by stronger correlation coefficients computed in the Mantel tests. This might be explained by seasonal dynamics of Changjiang Diluted Waters (i.e., the mixing of the Changjiang runoff with inshore water of the East China Sea) that changed the environmental conditions of coastal area dramatically, resulting in lower importance of spatial factors (dispersal limitation) on PCCs compared with environmental filters, including physicochemical properties (e.g., water temperature, salinity, dissolved oxygen, and nutrients), as well as biotic factors (e.g., Chl a and food abundance). This was further explained by higher immigration rate and fitness to neutral model, which suggested a predominant role of neutral process in shaping the PCCs in coastal area. Different richness, diversity, and taxonomic compositions but comparable biogeographic patterns were observed among abundant and rare sub-communities. In general, the abundant sub-communities exhibited higher dispersal ability which tend to respond to environmental selection during dispersal, whereas the rare sub-communities appeared to be present only in few samples due to dispersal limitation. Co-occurrence network further indicated the importance of biotic interactions in community assembly and potential roles of rare taxa in maintaining the community structure. Overall, this study suggests the dynamic in the biogeographic patterns of PCCs of the Changjiang plume to the adjacent waters in the ECS responding with the changing environmental conditions and geographical factors.

Toxic effects of phenanthrene intensify with an increase of temperature for the populations of a free-living nematode

Phenanthrene is one of the most common Polycyclic Aromatic Hydrocarbons (PAHs) in the marine environment. It has high lipoafinity and environmental persistence and tends to accumulate in benthic ecosystems. Exposure to phenanthrene can have severe impacts on a wide range of marine organisms, from nematodes to fish. These effects can be exacerbated with concurrent warming associated with climate change. In this study we investigated the response of free-living nematode populations of the species Diplolaimelloides delyi following exposure to different phenanthrene concentrations under normal and increased temperature conditions (from 25 °C up to 35 °C). Phenanthrene was toxic to D. delyi, causing a decrease in population growth (at concentrations ≥1 μg ml−1) and negatively affecting their development times and reproduction (at concentrations ≥2.5 μg ml−1). The observed effects intensified with increasing temperature, leading to further reduced development and population growth rate, arrested reproduction, and even mortality in 100% of the populations exposed to phenanthrene concentrations over 5 μg ml−1 at the highest temperature used (30 °C). Thermal-induced toxicity effects on marine populations can be significant, and current climate change and warming may have substantial implications for marine food webs and ecosystem functioning.

Intraspecific size variation in planktonic foraminifera cannot be consistently predicted by the environment.

The size structure of plankton communities is an important determinant of their functions in marine ecosystems. However, few studies have quantified how organism size varies within species across biogeographical scales. Here, we investigate how planktonic foraminifera, a ubiquitous zooplankton group, vary in size across the tropical and subtropical oceans of the world. Using a recently digitized museum collection, we measured shell area of 3,799 individuals of nine extant species in 53 seafloor sediments. We first analyzed potential size biases in the collection. Then, for each site, we obtained corresponding local values of mean annual sea‐surface temperature (SST), net primary productivity (NPP), and relative abundance of each species. Given former studies, we expected species to reach largest shell sizes under optimal environmental conditions. In contrast, we observe that species differ in how much their size variation is explained by SST, NPP, and/or relative abundance. While some species have predictable size variation given these variables (Trilobatus sacculifer, Globigerinoides conglobatus, Globigerinella siphonifera, Pulleniatina obliquiloculata, Globorotalia truncatulinoides), other species show no relationships between size and the studied covariates (Globigerinoides ruber, Neogloboquadrina dutertrei, Globorotalia menardii, Globoconella inflata). By incorporating intraspecific variation and sampling broader geographical ranges compared to previous studies, we conclude that shell size variation in planktonic foraminifera species cannot be consistently predicted by the environment. Our results caution against the general use of size as a proxy for planktonic foraminifera environmental optima. More generally, our work highlights the utility of natural history collections and the importance of studying intraspecific variation when interpreting macroecological patterns.

Functional traits explain trophic allometries of cephalopods.

Individual body size strongly influences the trophic role of marine organisms and the structure and function of marine ecosystems. Quantifying trophic position-individual body size relationships (trophic allometries) underpins the development of size-structured ecosystem models to predict abundance and the transfer of energy through ecosystems. Trophic allometries are well studied for fishes but remain relatively unexplored for cephalopods. Cephalopods are important components of coastal, oceanic and deep-sea ecosystems, and they play a key role in the transfer of biomass from low trophic positions to higher predators. It is therefore important to resolve cephalopod trophic allometries to accurately represent them within size-structured ecosystem models. We assessed the trophic positions of cephalopods in an oceanic pelagic (0-500m) community (sampled by trawling in a cold-core eddy in the western Tasman Sea), comprising 22 species from 12 families, using bulk tissue stable isotope analysis and amino acid compound-specific stable isotope analysis. We assessed whether ontogenetic trophic position shifts were evident at the species-level and tested for the best predictor of community-level trophic allometry among body size, taxonomy and functional grouping (informed by fin and mantle morphology). Individuals in this cephalopod community spanned two trophic positions and fell into three functional groups on an activity level gradient: low, medium and high. The relationship between trophic position and ontogeny varied among species, with the most marked differences evident between species from different functional groups. Activity-level-based functional group and individual body size are best explained by cephalopod trophic positions (marginal R2 =0.43). Our results suggest that the morphological traits used to infer activity level, such as fin-to-mantle length ratio, fin musculature and mantle musculature are strong predictors of cephalopod trophic allometries. Contrary to established theory, not all cephalopods are voracious predators. Low activity level cephalopods have a distinct feeding mode, with low trophic positions and little-to-no ontogenetic increases. Given the important role of cephalopods in marine ecosystems, distinct feeding modes could have important consequences for energy pathways and ecosystem structure and function. These findings will facilitate trait-based and other model estimates of cephalopod abundance in the changing global ocean.

Influence of Regional Oceanography and Hydrothermal Activity on Protist Diversity and Community Structure in the Okinawa Trough.

Microbial eukaryotes (protists) contribute substantially to ecological functioning in marine ecosystems, but the relative importance of factors shaping protist diversity, such as environmental selection and dispersal, remains difficult to parse. Water masses of a back-arc basin with hydrothermal activity provide a unique opportunity for studying the effects of dispersal and environmental selection on protist communities. In this study, we used metabarcoding to characterize protist communities in the Okinawa Trough, a back-arc spreading basin containing at least twenty-five active hydrothermal vent fields. Water was sampled from four depths at fourteen stations spanning the length of the Okinawa Trough, including three sites influenced by nearby hydrothermal vent sites. While significant differences in community structure reflecting water depth were present, protist communities were mostly homogeneous horizontally. Protist communities in thebottom waters affected by hydrothermal activity were significantly different from communities in other bottom waters, suggesting that environmental factors can be especially important in shaping community composition under specific conditions. Amplicon sequence variants that were enriched in hydrothermally influenced bottom waters largely derived from cosmopolitan protists that were present, but rare, in other near-bottom samples, thus highlighting the importance of the rare biosphere.

Distinct fungal communities associated with different organs of the mangrove Sonneratia alba in the Malay Peninsula

Mangrove forests are key tropical marine ecosystems that are rich in fungi, but our understanding of fungal communities associated with mangrove trees and their various organs remains limited because much of the diversity lies within the microbiome. In this study, we investigated the fungal communities associated with the mangrove tree Sonneratia alba throughout Peninsular Malaysia and Singapore. At each sampling location, we collected leaves, fruits, pneumatophores and sediment samples and performed amplicon sequencing of the ribosomal internal transcribed spacer 1 to characterise the associated communities. Results show distinct fungal communities at each sampled location with further differentiation according to the plant part. We find a significant distance decay of similarity, particularly for sediment samples due to the greater variability of sediment environments relative to the more stable fungal habitats provided by living plant organs. We are able to assign taxonomy to the majority of sequences from leaves and fruits, but a much larger portion of the sequences recovered from pneumatophores and sediment samples could not be identified. This pattern underscores the limited mycological research performed in marine environments and demonstrates the need for a concerted research effort on multiple species to fully characterise the coastal microbiome and its role in the functioning of marine ecosystems.

Microplastic accumulation via trophic transfer: Can a predatory crab counter the adverse effects of microplastics by body defence?

Microplastics are considered detrimental to aquatic organisms due to their potential accumulation along food chains. Thus, it is puzzling why some of them appear unaffected by microplastics. Here, we assessed the contribution of water filtration and food consumption to microplastic accumulation in a predatory marine crab (Charybdis japonica) and examined the associated impacts of microplastics (particle size: 5 μm) following ingestion for one week. Results showed that water filtration and food consumption contributed similarly to the accumulation of microplastics, which were distributed among organs in this order: hepatopancreas > guts > gills > muscles. Yet, biomagnification (i.e. accumulation through consumption of microplastic-contaminated mussels) did not occur possibly due to egestion of microplastics. The crabs upregulated detoxification capacity (EROD) and antioxidant defence (GST) in response to the microplastics accumulated in their tissues. However, these defence mechanisms collapsed when the microplastic concentration in hepatopancreas exceeded ~3 mg g−1, leading to severe hepatic injury (elevated AST and ALT) and impaired neural activity (reduced AChE). Our results suggest that marine organisms have an innate capacity to counter the acute effects of microplastics, but there is a limit beyond which the defence mechanisms fail and hence physiological functions are impaired. As microplastic pollution will deteriorate in the future, the fitness and survival of marine organisms may be undermined by microplastics, affecting the stability and functioning of marine ecosystems.

Global Systematic Review of Methodological Approaches to Analyze Coastal Shelf Food Webs

The study of marine coastal food webs has a central role in the application of the integrated ecosystem approach for marine management. Changes in food webs caused by natural or anthropic drivers can lead to dramatic shifts in the overall structure and function of coastal marine ecosystems and deterioration of their services. The present review investigates the methodological approaches employed for the assessment of coastal shelf food webs at a global scale and highlights existing gaps and limitations. Out of 1652 published articles that initially met our search criteria, 880 passed the initial screening and 493 were found relevant and were fully analysed. The information extracted included the spatiotemporal coverage of the studies; the main methodological approaches utilized for the assessment of population state variables (i.e. biomass, size, abundance) and trophic levels; the biotic components and driving factors considered; indices used to describe the structure and functioning of coastal food webs; and main knowledge gaps. Results showed that most studies have been conducted at a subnational level, mostly in the Temperate Northern Atlantic marine realm. Overall, 54% of the studies provided quantitative information on food web structure. The most common methodological approach utilized was modelling (40%), followed by non-experimental-based correlations (30%), and natural or manipulative experiments (14%). Information on population state variables was provided by 69% of the studies, while 42% employed some of the following trophic level determination techniques: stable isotopes, gut contents, fatty acids, and molecular analysis, which were either combined or used in isolation. Specific natural or human drivers were incorporated in 76% of the studies, with fishing being the most common driver. Modelling approaches included multiple indices to describe food web attributes and/or the structure and functioning of coastal shelf ecosystems. Despite the great progress achieved through the development of new tools and techniques, food web analysis still suffers from important knowledge gaps and limitations of the methodological approaches, which are extensively discussed. The present review establishes a useful knowledge base to provide guidance for future research and assessments on coastal shelf food webs, and to support ecosystem-based management.

Range‐extending tropical herbivores increase diversity, intensity and extent of herbivory functions in temperate marine ecosystems

Abstract Climate change is modifying species distributions around the world, forcing some species poleward, where they can alter trophic interactions. Many tropical herbivorous fishes have successfully expanded their ranges into temperate ecosystems, and while it is clear they drive increases in herbivory rates in specific localities, little is known about how they might affect the diversity of herbivory functions across large spatial scales, considering their interaction with assemblages of native herbivores in temperate habitats. We assessed the spatial overlap and habitat associations of native temperate and range‐expanding tropical herbivorous fishes in six subregions of south‐western Australia to determine how incursions of tropical species may have affected the diversity, redundancy (index of uniqueness) and the ‘spatial extent’ (addition of functions in new areas) and ‘intensity’ (increasing density of functional groups) of specific herbivory functions in recipient ecosystems. Tropical herbivores had high abundances in temperate ecosystems, forming schools from 40 (parrotfish) to 200 (rabbitfish) individuals strongly associated with seagrass meadows and reefs with high cover of turf algae. Overlap with temperate herbivores was highest in the northern subregions, forming unique assemblages, with no apparent species displacements. The addition of tropical species increased functional diversity and uniqueness (the complement of redundancy), introducing novel herbivory functions to many locations. Seagrass browsing increased in spatial extent (27%) and intensity (15×), while seaweed browsing and grazing increased in intensity by up to 2.5× in regions with high abundances of tropical herbivores. Our results suggest that the diversity, intensity and spatial extent of different herbivory functions can change as tropical species with different habitat affinities, behaviours and diets shift their distributions poleward. Changes in functional redundancy are likely to be heterogeneous in space and might not increase initially because the diversity of herbivory functions is relatively low in some temperate marine ecosystems. However, there is the potential for greater redundancy as further tropical species arrive, their abundances increase and the spatial and functional overlap of communities rises. A free Plain Language Summary can be found within the Supporting Information of this article.