Environmental stressors, complex interactions and marine benthic communities' responses

Metabolomic and biochemical disorders reveal the toxicity of environmental microplastics and benzo[a]pyrene in the marine polychaete Hediste diversicolor

Recently, the abundance of environmental microplastics (MPs) has become a global paramount concern. Besides the danger of MPs for biota due to their tiny size, these minute particles may act as vectors of other pollutants. This study focused on evaluating the toxicity of environmentally relevant concentrations of MPs (10 and 50 mg/kg sediment) and benzo[a]pyrene (B[a]P, 1 µg/kg sediment), alone and in mixture, for 3 and 7 days in marine polychaete Hediste diversicolor, selected as a benthic bioindicator model. The exposure period was sufficient to confirm the bioaccumulation of both contaminants in seaworms, as well as the potential capacity of plastic particles to adsorb and vehiculate the B[a]P. Interestingly, increase of acidic mucus production was observed in seaworm tissues, indicative of a defense response. The activation of oxidative system pathways was demonstrated as a strategy to prevent lipid peroxidation. Furthermore, the comprehensive Nuclear Magnetic Resonance (NMR)-based metabolomics revealed significant disorders in amino acids metabolism, osmoregulatory process, energetic components, and oxidative stress related elements. Overall, these findings proved the possible synergic harmful effect of MPs and B[a]P even in small concentrations, which increases the concern about their long-term presence in marine ecosystems, and consequently their transfer and repercussions on marine fauna.

Comprehensive biochemical analysis and nutritional evaluation of fatty acid and amino acid profiles in eight seahorse species (Hippocampus spp.)

Seahorses are increasingly recognized for their nutritional potential, which underscores the necessity for comprehensive biochemical analyses. This study aims to investigate the fatty acid and amino acid compositions of eight seahorse species, including both genders of Hippocampus trimaculatus, Hippocampus kelloggi, Hippocampus abdominalis, and Hippocampus erectus, to evaluate their nutritional value. We employed Gas Chromatography-Mass Spectrometry (GC-MS) and High-Performance Liquid Chromatography (HPLC) to analyze the fatty acid and amino acid profiles of the seahorse species. GC-MS was used to detect 34 fatty acid methyl esters, while HPLC provided detailed amino acid profiles. GC-MS analysis demonstrated high precision with relative standard deviations (RSDs) generally below 2.53 %, satisfactory repeatability (RSDs from 6.55 % to 8.73 %), and stability (RSDs below 2.82 %). Recovery rates for major fatty acids ranged from 98.73 % to 109.12 %. HPLC analysis showed strong separation of amino acid profiles with theoretical plate numbers exceeding 5000. Precision tests yielded RSDs below 1.23 %, with reproducibility and stability tests showing RSDs below 2.73 % and 2.86 %, respectively. Amino acid recovery rates ranged from 97.58 % to 104.66 %. Nutritional analysis revealed significant variations in fatty acid content among the species. Female H. erectus showed higher levels of hexadecanoic acid and saturated fatty acids, while male H. abdominalis had lower concentrations of n-3 full cis 4,7,10,13,16,19-docosahexaenoic acid (DHA). Total lipid yields varied from 3.2491 % to 12.3175 %, with major fatty acids constituting 17.9717 %-74.6962 % of total lipids. In conclusion, this study provides essential insights into the fatty acid and amino acid composition of seahorses, supporting their potential as valuable dietary supplements. The differences between genders in specific fatty acids suggest a nuanced nutritional profile that could be exploited for targeted dietary applications. Further research is needed to explore the seasonal and environmental variations affecting seahorse biochemical composition.

Oil and gas platforms degrade benthic invertebrate diversity and food web structure

Oil and gas exploitation introduces toxic contaminants such as hydrocarbons and heavy metals to the surrounding sediment, resulting in deleterious impacts on marine benthic communities. This study combines benthic monitoring data over a 30-year period in the North Sea with dietary information on >1400 taxa to quantify the effects of active oil and gas platforms on benthic food webs using a multiple before-after control-impact experiment. Contamination from oil and gas platforms caused declines in benthic food web complexity, community abundance, and biodiversity. Fewer trophic interactions and increased connectance indicated that the community became dominated by generalists adapting to alternative resources, leading to simpler but more connected food webs in contaminated environments. Decreased mean body mass, shorter food chains, and the dominance of small detritivores such as Capitella capitata near to structures suggested a disproportionate loss of larger organisms from higher trophic levels. These patterns were associated with concentrations of hydrocarbons and heavy metals that exceed OSPAR's guideline thresholds of sediment toxicity. This study provides new evidence to better quantify and manage the environmental consequences of oil and gas exploitation at sea.

Exposure to nanopollutants (nZnO) enhances the negative effects of hypoxia and delays recovery of the mussels' immune system

Aquatic environments face escalating challenges from multiple stressors like hypoxia and nanoparticle exposure, with impact of these combined stressors on mussel immunity being poorly understood. We investigated the individual and combined effects of short-term and long-term hypoxia and exposure to zinc oxide nanoparticles (nZnO) on immune system of the mussels (Mytilus edulis). Hemocyte functional traits (mortality, adhesion capacity, phagocytosis, lysosomal abundance, and oxidative burst), and transcript levels of immune-related genes involved in pathogen recognition (the Toll-like receptors, the complement system components, and the adaptor proteins MyD88) were assessed. Short-term hypoxia minimally affected hemocyte parameters, while prolonged exposure led to immunosuppression, impacting hemocyte abundance, viability, phagocytosis, and defensin gene expression. Under normoxia, nZnO stimulated immune responses of mussel hemocytes. However, combined nZnO and hypoxia induced more pronounced and rapid immunosuppression than hypoxia alone, indicating a synergistic interaction. nZnO exposure hindered immune parameter recovery during post-hypoxic reoxygenation, suggesting persistent impact. Opposing trends were observed in pathogen-sensing and pathogen-elimination mechanisms, with a positive correlation between pathogen-recognition system activation and hemocyte mortality. These findings underscore a complex relationship and potential conflict between pathogen-recognition ability, immune function, and cell survival in mussel hemocytes under hypoxia and nanopollutant stress, and emphasize the importance of considering multiple stressors in assessing the vulnerability and adaptability of mussel immune system under complex environmental conditions of anthropogenically modified coastal ecosystems.

Unraveling the interplay between environmental microplastics and salinity stress on Mytilus galloprovincialis larval development: A holistic exploration

The rise of plastic production has triggered a surge in plastic waste, overwhelming marine ecosystems with microplastics. The effects of climate change, notably changing salinity, have shaped the dynamics of coastal lagoons. Thus, understanding the combined impact of these phenomena on marine organisms becomes increasingly crucial. To address these knowledge gaps, we investigated for the first time the interactive effects of environmental microplastics (EMPs) and increased salinity on the early development of Mytilus galloprovincialis larvae. Morphological assessments using the larval embryotoxicity test revealed larval anomalies and developmental arrests induced by EMPs and increased salinity. Transcriptomic analyses targeting 12 genes involved in oxidative stress, apoptosis, DNA repair, shell formation, and stress proteins were conducted on D-larvae uncovered the potential effects of EMPs on shell biomineralization, highlighting the role of Histidine Rich Glycoproteine (HRG) and tubulin as crucial adaptive mechanisms in Mytilus sp. in response to environmental shifts. Furthermore, we explored oxidative stress and neurotoxicity using biochemical assays. Our findings revealed a potential interaction between EMPs and increased salinity, impacting multiple physiological processes in mussel larvae. Our data contribute to understanding the cumulative effects of emerging anthropogenic pollutants and environmental stressors, emphasizing the need for a holistic approach to assessing their impact on marine ecosystems.

Determination of potentially toxic elements bioaccumulated in the commercially important pelagic fish narrow-barred Spanish mackerel (Scomberomorus commerson)

Anthropogenic activities have increased the discharge of marine contaminants threatening marine life. Small gulfs, such as the Arabian Gulf, are vulnerable to accumulating potentially toxic elements in marine species due to slow water exchange. The concentration of 21 elements was determined in the tissues of Scomberomorus commerson from Umm Al Quwain (United Arab Emirates) and Bandar Abbas (Iran). Chromium, Copper, and Iron exceeded internationally established maximum permissible limits. Sites could not be distinguished based on Principle Component Analyses of elements. Elevated Cu and Cr in muscle are of concern to marine species as well as humans. Metal Pollution Index showed a significant difference between sites, with 20.34 % and 100 % of individuals suffering high metal toxicity and poor body conditions, respectively. The Arabian Gulf is experiencing an increase in discharge of industrial wastes. Implementation of strict policies to reduce discharge of toxic substances is required to protect marine organisms and humans.

Behavioral responses of intertidal clams to compound extreme weather and climate events

Rapidly increasing concentration of carbon dioxide (CO2) in the atmosphere not only results in global warming, but also drives increasing seawater acidification. Infaunal bivalves play critical roles in benthic-pelagic coupling, but little is known about their behavioral responses to compound climate events. Here, we tested how heatwaves and acidification affected the behavior of Manila clams (Ruditapes philippinarum). Under acidified conditions, the clams remained capable of burrowing into sediments. Yet, when heatwaves attacked, significant decreases in burrowing ability occurred. Following two consecutive events of heatwaves, the clams exhibited rapid behavioral acclimation. The present study showed that the behavior of R. philippinarum is more sensitive to heatwaves than acidification. Given that the behavior can act as an early and sensitive indicator of the fitness of intertidal bivalves, whether, and to what extent, behavioral acclimation can persist under scenarios of intensifying heatwaves in the context of ocean acidification deserve further investigations.

Submarine outfall and new sewage treatment plant modulate the response of intertidal benthic communities in a SW Atlantic area

Spatio-temporal responses of the intertidal macrobenthic community to the effects of a submarine outfall (SO) and a new sewage treatment plant (EDAR) were evaluated, analyzing changes in macrofaunal assemblages and community structure. Study was conducted in a SW Atlantic coastal area in 4 stages: BSO (Before the SO), Du (During the construction of the SO), ASO (After the SO start-up) and AEDAR (After the treatment plant start-up). Boccardia proboscidea and Brachidontes rodriguezii contributed most to the differences between all stages at the site nearest to the discharge point. Number of individuals was highest at BSO and Du. Richness and diversity were lowest at the BSO and highest at the Du. Furthermore, the richness decreased slightly, and the diversity increased at AEDAR. Evenness was highest at the BSO and AEDAR. The nestedness was the dominant process driving the differences between the BSO stage community and the rest of the stages. SO affects the composition and structure of the intertidal macrobenthic community near the outfall area, as organic matter discharge further offshore favour the development of a more diverse intertidal community, including species sensitive to organic enrichment.

Influence of hydraulic clam dredging and seasonal environmental changes on macro-benthic communities in the Southern Adriatic (Central Mediterranean Sea)

Macro-benthic communities on the shallowest soft bottoms are impacted by hydraulic dredgers used for the harvesting of the striped venus clam (Chamelea gallina). Changes in macro-benthic assemblages were analysed across four areas in the Southern Adriatic Sea (Central Mediterranean Sea) during the winter and summer 2022 (low and high fishing pressures, respectively). Two sampling surveys were carried out collecting abundance data (N/100m2) of 69 species. Diversity indices (Shannon-Weiner and Equitability) were calculated and differences between seasons and areas were tested using non-parametric tests. Changes in the assemblage and feeding habits were explored by adopting permutational multivariate analysis of variance on 34 species. Moreover, environmental conditions of all areas in the two seasons were characterized by a set of 8 variables. Seasonal changes in diversity were only detected for the Shannon-Weiner index, with values significantly higher in winter than summer. Macro-benthic assemblages differed between the two seasons, and the winter assemblages were well-distinct in each area. In contrast, a high overlap was shown in the summer assemblages of the four areas. Changes in feeding habits showed an increase in filter feeding polychaetes and opportunistic/scavenger species during the summer. Temperature, Salinity and primary production were positively correlated to summer stations indicating potential thermic stress on the assemblages. The results provide information on the benthic community impacted by dredge disturbance and seasonal changes driven by environmental conditions, stressing the need to integrate these aspects in assessments on the health status of marine ecosystems required by European directives and fishery management plans.

Stressor fluctuations alter mechanisms of seagrass community responses relative to static stressors

Ecosystems are increasingly affected by multiple anthropogenic stressors that contribute to habitat degradation and loss. Natural ecosystems are highly dynamic, yet multiple stressor experiments often ignore variability in stressor intensity and do not consider how effects could be mediated across trophic levels, with implications for models that underpin stressor management. Here, we investigated the in situ effects of changes in stressor intensity (i.e., fluctuations) and synchronicity (i.e., timing of fluctuations) on a seagrass community, applying the stressors reduced light and physical disturbance to the sediment. We used structural equation models (SEMs) to identify causal effects of dynamic multiple stressors on seagrass shoot density and leaf surface area, and abundance of associated crustaceans. Responses depended on whether stressor intensities fluctuated or remained static. Relative to static stressor exposure at the end of the experiment, shoot density, leaf surface area, and crustacean abundance all declined under in-phase (synchronous; 17, 33, and 30 % less, respectively) and out-of-phase (asynchronous; 11, 28, and 39 % less, respectively) fluctuating treatments. Static treatment increased seagrass leaf surface area and crustacean abundance relative to the control group. We hypothesised that crustacean responses are mediated by changes in seagrass; however, causal analysis found only weak evidence for a mediation effect via leaf surface area. Changes in crustacean abundance, therefore, were primarily a direct response to stressors. Our results suggest that the mechanisms underpinning stress responses change when stressors fluctuate. For instance, increased leaf surface area under static stress could be caused by seagrass acclimating to low light, whereas no response under fluctuating stressors suggests an acclimation response was not triggered. The SEMs also revealed that community responses to the stressors can be independent of one another. Therefore, models based on static experiments may be representing ecological mechanisms not observed in natural ecosystems, and underestimating the impacts of stressors on ecosystems.

Multi-biomarker approach for the (eco)toxicity of UV-filter environmental pollution on the Mediterranean mussel Mytilus galloprovincialis in a multiple stressor context. The case of 4-MBC under salinity shifts

Marine-coastal ecosystems are rapidly transforming because of climate change (CC). At the same time, the impacts of emerging organic contaminants (i.e., organic UV-filters) on these ecosystems are intensifying. In the Mediterranean, the consequences of these disturbances are occurring at a fast pace making this area a potential sentinel site to be investigated. While singular effects of organic UV-filters or CC-related factors on marine biota have been relatively described, their combined impact is still largely unknown. Thus, the objective of this study was to assess the long-term responses of the Mediterranean mussel Mytilus galloprovincialis towards anticipated salinity changes (decreases-S20 or increases-S40) when exposed to environmentally relevant concentrations of the UV-filter 4-methylbenzylidene camphor (4-MBC). An integrated multi-biomarker approach was applied, featuring general and oxidative stress, antioxidant and biotransformation enzyme capacity, energy metabolism, genotoxicity, and neurotoxicity biomarkers. Results showed that both projected salinities, considered separately, exerted non-negligible impacts on mussels' health status, with greater biological impairments found at S 40. Combining both stressors resulted in an evident increase in mussels' susceptibility to the UV-filter, which exacerbated the toxicity of 4-MBC. The dominant influence of salinity in the climate change-contaminant interaction played a crucial role in this outcome. The most severe scenario occurred when S 20 was combined with 4-MBC. In this situation, mussels exhibited a decrease in filtration rate, metabolic capacity and deployment of energy reserves increased, with an upregulation of biotransformation and inhibition of antioxidant enzyme activities. This exposure also led to the observation of cellular and DNA damage, as well as an increase in AChE activity. Furthermore, salinity-dependent bioaccumulation patterns were evaluated revealing that the lowest values in contaminated mussels are found at S 20. Overall, the present findings provide evidence that projected CC/pollutant scenarios may represent high risks for mussels' populations, with global relevant implications for the ecosystem level.

Tipping point arises earlier under a multiple-stressor scenario

Anthropogenic impacts and global changes have profound implications for natural ecosystems and may lead to their modification, degradation or collapse. Increases in the intensity of single stressors may create abrupt shifts in biotic responses (i.e. thresholds). The effects of multiple interacting stressors may create non-additive responses, known as synergistic or antagonistic interactions. Here we combine both concepts-ecological thresholds and interactions between multiple stressors-to understand the effects of multiple interacting stressors along environmental gradients, and how this can affect the occurrence of thresholds. Using an experimental approach to investigate the effect of nutrient enrichment and saltwater intrusion on mortality in the zebra mussel, Dreissena polymorpha, we show that multiple stressors can create thresholds at lower levels of an environmental gradient. Our results reveal a major shortcoming in how we currently investigate these two ecological concepts, as considering them separately may be causing underestimation of thresholds and stressor-interaction impacts.

The relative roles of multiple drivers on benthic ciliate communities in an intertidal zone

Intertidal biodiversity is being severely disrupted as a result of increased anthropogenic activity. However, our knowledge about how natural gradients, human induced disturbance and biotic interactions affect biodiversity is limited. So, we investigated how three facets of alpha diversity and community composition of benthic ciliates responded to environmental and biological gradients in the intertidal zone of Zhejiang, China. The key determinants and their relative effects on ciliate communities were identified using structural equation modeling, distance-based redundancy analysis and variation partitioning analysis. Our results revealed that sediment grain size was the most important factor affecting alpha diversity and community composition. Human induced eutrophication had significant effects on phylogenetic alpha diversity and community composition. However, the effects of biotic interactions on ciliate communities were relatively small. Moreover, we found community composition was more sensitive to human disturbance than alpha diversity, thus, more suitable for indicating human-induced eutrophication.

Are physiological responses in foraminifera reliable environmental stress bioindicators? A systematic review

Foraminifera are considered good bioindicators of environmental stress based on morphological abnormalities, but physiological responses occur far earlier and have not been evaluated as pollution markers. The aim of this review was to collate all published articles reporting physiological changes in foraminifera after environmental and anthropogenic stressors, to evaluate their reliability as early markers of environmental stress. We reviewed 70 studies, meeting the inclusion criteria, reporting 13 physiological effects classes after exposure to 17 different stressors. Immune functions, bleaching and lifecycle disruptions, were the most reported. Amphistegina and Ammonia showed high proportion of effects with lead and mercury, with a significant relationship between these heavy metals and the number of physiological effects classes in Ammonia, and between bleaching in Amphistegina gibbosa and Amphistegina lobifera with solar light and temperature. This suggests physiological responses are potentially reliable early indicators of environmental stress. It is necessary to increase quantitative physiological measures and standard exposure protocols in order to properly evaluate these organisms as pollution bioindicators.

Indication of the impact of environmental stress on the responses of the bivalve mollusk Unio tumidus to ibuprofen and microplastics based on biomarkers of reductive stress and apoptosis

The vulnerability of bivalve mollusks to micropollutants is estimated mainly in single model exposures. However, chronic environmental stress and complex exposures can modulate their responses. To evaluate the impact of population-dependent adaptations on the ability to react to common micropollutants, we compared freshwater bivalves Unio tumidus from two distinct populations, pure (Pr) and contaminated (Ct), in their exposures to microplastics (MP, 1 mg L^-1, size 0.1-0.5 mm), pharmaceutical ibuprofen (IBU, 0.8 μg L^-1), or their combination (Mix) for 14 days. Control groups from both sites showed remarkable differences, with lower levels of total antioxidant capacity (TAC), metallothionein protein (MTSH), NADH and NAD⁺, cytochrome P450-related EROD, glutathione-S transferase (GST), and citrate synthase (CS) but higher levels of GSH, GSSG, caspase-3 and cathepsin D (CTD) in the Ct-control group. These data indicate a chronic stress impact in the Ct population. Under exposures, we found an almost common strategy in both populations for NAD⁺/NADH and MTSH suppression and CTD induction. Additionally, Mix exposure caused an increase in CS, and IBU did not change GSH in both populations. However, the expected response to IBU - the suppression of caspase-3 - was indicated only in PrIBU- and PrMix-mollusks. CTD efflux increased dramatically only in PrMP- and PrMix- groups, and suppression of EROD and GST was detected in the PrMix-group. According to discriminant analysis, exposed Pr-groups were highly differentiated from control, whereas Ct-control and exposed groups had common localization demonstrating high resistance to environmental stress. Thus, the same exposures resulted in different adverse outcome pathways depending on the population.

Anthropogenic impact on the reproductive health of two wild Patagonian fish species with differing reproductive strategies

A particularly concerning outcome of environmental pollution is the disturbance of reproductive processes. However, studies on the impacts of pollution on the reproductive health of fish inhabiting South American environments are limited. We studied the impact of anthropogenic pollution on the reproductive health of two sympatric Patagonian marine fish species with different reproductive strategies: the live-bearing rockfish Sebastes oculatus and the egg-laying Brazilian sandperch Pinguipes brasilianus. Our findings reveal that both species presented some degree of reproductive disturbance when inhabiting an affected site, but the specific alterations differed depending on the species, sex, and season. During the reproductive season, 17β-estradiol levels were elevated in females of both species living in polluted areas, while no differences in androgen levels were observed in either species or season. The gonadosomatic index (GSI) was affected in both sexes of S. oculatus during the non-reproductive season, while the gonadal stages were mainly affected in both sexes of P. brasilianus. No signs of intersex condition were observed. Our results highlight the importance of including diverse reproductive parameters to better understand anthropogenic effects on wild animals. Long-term studies including other fish species and including offspring (to evaluate possible transgenerational effects) will be necessary to determine the consequences of the documented reproductive alterations, particularly whether fish species inhabiting Patagonian marine reef areas will be able to reproductively adapt to increasing marine anthropogenic disturbances.

Metagenomics to characterize sediment microbial biodiversity associated with fishing exposure within the Stellwagen Bank National Marine Sanctuary

Microbes in marine sediments constitute a large percentage of the global marine ecosystem and function to maintain a healthy food web. In continental shelf habitats such as the Gulf of Maine (GoM), relatively little is known of the microbial community abundance, biodiversity, and natural product potential. This report is the first to provide a time-series assessment (2017–2020) of the sediment microbial structure in areas open and closed to fishing within the Stellwagen Bank National Marine Sanctuary (SBNMS). A whole metagenome sequencing (WMS) approach was used to characterize the sediment microbial community. Taxonomic abundance was calculated across seven geographic sites with 14 individual sediment samples collected during the summer and fall seasons. Bioinformatics analyses identified more than 5900 different species across multiple years. Non-metric multidimensional scaling methods and generalized linear models demonstrated that species richness was inversely associated with fishing exposure levels and varied by year. Additionally, the discovery of 12 unique biosynthetic gene clusters (BGCs) collected across sites confirmed the potential for medically relevant natural product discovery in the SBNMS. This study provides a practical assessment of how fishing exposure and temporal trends may affect microbial community structure in a coastal marine sanctuary.

Omics-based ecosurveillance for the assessment of ecosystem function, health, and resilience

Current environmental monitoring efforts often focus on known, regulated contaminants ignoring the potential effects of unmeasured compounds and/or environmental factors. These specific, targeted approaches lack broader environmental information and understanding, hindering effective environmental management and policy. Switching to comprehensive, untargeted monitoring of contaminants, organism health, and environmental factors, such as nutrients, temperature, and pH, would provide more effective monitoring with a likely concomitant increase in environmental health. However, even this method would not capture subtle biochemical changes in organisms induced by chronic toxicant exposure. Ecosurveillance is the systematic collection, analysis, and interpretation of ecosystem health-related data that can address this knowledge gap and provide much-needed additional lines of evidence to environmental monitoring programs. Its use would therefore be of great benefit to environmental management and assessment. Unfortunately, the science of ‘ecosurveillance’, especially omics-based ecosurveillance is not well known. Here, we give an overview of this emerging area and show how it has been beneficially applied in a range of systems. We anticipate this review to be a starting point for further efforts to improve environmental monitoring via the integration of comprehensive chemical assessments and molecular biology-based approaches. Bringing multiple levels of omics technology-based assessment together into a systems-wide ecosurveillance approach will bring a greater understanding of the environment, particularly the microbial communities upon which we ultimately rely to remediate perturbed ecosystems.

Omics-based ecosurveillance uncovers the influence of estuarine macrophytes on sediment microbial function and metabolic redundancy in a tropical ecosystem

Vertical zonation within estuarine ecosystems can strongly influence microbial diversity and function by regulating competition, predation, and environmental stability. The degree to which microbial communities exhibit horizontal patterns through an estuary has received comparatively less attention. Here, we take a multi-omics ecosurveillance approach to study environmental gradients created by the transition between dominant vegetation types along a near pristine tropical river system (Wenlock River, Far North Queensland, Australia). The study sites included intertidal mudflats fringed by saltmarsh, mangrove or mixed soft substrata habitats. Collected sediments were analyzed for eukaryotes and prokaryotes using small sub-unit (SSU) rRNA gene amplicons to profile the relative taxonomic composition. Central carbon metabolism metabolites and other associated organic polar metabolites were analyzed using established metabolomics-based approaches, coupled with total heavy metals analysis. Eukaryotic taxonomic information was found to be more informative of habitat type. Bacterial taxonomy and community composition also showed habitat-specificity, with phyla Proteobacteria and Cyanobacteria strongly linked to mangroves and saltmarshes, respectively. In contrast, metabolite profiling was critical for understanding the biochemical pathways and expressed functional outputs in these systems that were tied to predicted microbial gene function (16S rRNA). A high degree of metabolic redundancy was observed in the bacterial communities, with the metabolomics data suggesting varying degrees of metabolic criticality based on habitat type. The predicted functions of the bacterial taxa combined with annotated metabolites accounted for the conservative perspective of microbial community redundancy against the putative metabolic pathway impacts in the metabolomics data. Coupling these data demonstrates that habitat-mediated estuarine gradients drive patterns of community diversity and metabolic function and highlights the real redundancy potential of habitat microbiomes. This information is useful as a point of comparison for these sensitive ecosystems and provides a framework for identifying potentially vulnerable or at-risk systems before they are significantly degraded.

Evaluating Multiple Stressor Effects on Benthic–Pelagic Freshwater Communities in Systems of Different Complexities: Challenges in Upscaling

Upscaling of ecological effects from indoor microcosms to outdoor mesocosms bridging the gap between controlled laboratory conditions and highly complex natural environments poses several challenges: typical standard water types used in laboratory experiments are not feasible in large outdoor experiments. Additionally, moving from the micro- to meso-scale, biodiversity is enhanced. We performed an indoor microcosm experiment to determine the effects of agricultural run-off (ARO) on a defined benthic–pelagic community comprising primary producers and primary consumers, exposed to ambient summer temperature and +3.5 °C. Treatments were replicated in two water types (standard Volvic and Munich well water). We then scaled up to outdoor mesocosms using an ARO concentration gradient and +3 °C warming above ambient temperature, using Munich well water. We included the same benthic macroorganisms but more complex periphyton and plankton communities. All the functional groups were affected by stressors in the microcosms, and a shift from macrophyte to phytoplankton dominance was observed. While effects were present, they were less pronounced in the mesocosms, where a higher biodiversity may have modified the responses of the system to the stressors. The stressor effects observed in controlled experiments may thus be masked in more complex outdoor experiments, but should not be interpreted as “no effects”.

Ocean acidification alters anti-predator responses in a competitive dominant intertidal mussel

Widespread intertidal mussels are exposed to a variety of natural and anthropogenic stressors. Even so, our understanding of the combined influence of stressors such as predation risk and ocean acidification (OA) on these species remains limited. This study examined the response of the purple mussel (Perumytilus purpuratus), a species distributed along Pacific southeastern rocky shores, to the effects of predation risk and OA. Using a laboratory 2 × 2 cross design, purple mussels were either devoid or exposed to predator cues from the muricid snail Acanthina monodon, while simultaneously exposing them to current (500 ppm) or projected OA conditions (1500 ppm). The response of purple mussels to these factors was assessed using growth, calcification, clearance, and metabolic rates, in addition to byssus production. After 60 d, the presence of predator cues reduced mussel growth in width and length, and in the latter case, OA enhanced this response making the effects of predator cues more severe. Calcification rates were driven by the interaction between the two stressors, whereas clearance rates increased only in response to OA, likely explaining some of the growth results. Mussel byssus production also increased with pCO₂ but interacted with predation risk: in the absence of predator cues, byssus production increased with OA. These results suggest that projected levels of OA may alter and in some cases prevail over the natural response of purple mussels to predation risk. Considering the role played by this mussel as a dominant competitor and ecosystem engineer in rocky shores, these results have community-wide implications.

Dynamics of Restored and Natural Oyster Reefs After a Hurricane

Restoration of shellfish reefs has increased exponentially over the past two decades, due in part to increased awareness of widespread oyster habitat loss. Large-scale, acute disturbances such as hurricanes have the potential to influence restoration outcomes, but because storm occurrence is unpredictable with respect to restoration timelines, the responses of restored habitats are not well understood. We quantified the ecological dynamics of a newly constructed Crassostrea virginica oyster reef and nearby reference reef in a Texas estuary immediately after Hurricane Harvey, a major category 4 storm. Biophysical structure (e.g., oyster density, shell height, sediment grain size), and community composition (abundance of reef-associated epifauna, and nearby infauna) were measured for 18 months. A sharp decrease in salinity and temporary deposition of fine sediments within the first 3 months corresponded with increases in oyster and epifaunal recruitment on the restored reef, although densities were generally below those measured on restored reefs without hurricanes. Criteria for oyster reef restoration success were met within 12–18 months post-storm. Infaunal densities decreased but returned to pre-storm densities within 2 months, but bivalves were delayed, returning to pre-storm levels after 9 months. A lack of historical baseline data on the newly restored reef limited our ability to assess the magnitude of reef recovery to pre-disturbance levels or separate the direct effects of the hurricane from the dynamics of early recruitment and growth. Results provide important information about restored and natural oyster reef dynamics after large-scale disturbance and can help inform effective management and conservation measures.

Early-stage anomalies in the sea urchin (Paracentrotus lividus) as bioindicators of multiple stressors in the marine environment: Overview and future perspectives

The morphological anomalies of the early development stages of the sea urchin Paracentrotus lividus, caused by exposure to environmental stressors, are used as biomarker in ecotoxicological and ecological investigations. Here, we reviewed the available literature and classified the embryo and larval anomalies identified so far, to highlight potential commonalities or differences related to the biological action of the different stressors and their ecological impact. Morphological anomalies are influenced by a) the developmental stage of exposure to stressors; b) the intensity of the stress; c) the intra- and inter-cellular mechanisms affected by the exposure to environmental agents. The classification and analysis of embryo and larvae anomalies, either observed by the authors of this review and reported in literature, indicate that sea urchin abnormalities, caused by exposure to different stressors, can be very similar among them and classified into 18 main types, which can occur individually or mixed. All anomalies can be used to calculate an Index of Contaminant Impact to assess the impact of multiple stressors and to identify relationships between morphological anomalies and compromised biological mechanisms. This approach could be useful for a first screening of the presence of potential stressors impairing the growth and development of the early life stages of marine organisms, thus providing a relevant advancement for in future monitoring activities devoted to assess the health status in coastal marine ecosystems.