Predicted levels of future ocean acidification and temperature rise could alter community structure and biodiversity in marine benthic communities

Climatic, oceanic, freshwater, and local environmental drivers of New Zealand estuarine macroinvertebrates

Understanding the responses of organisms to different environmental drivers is critical for improving ecosystem management and conservation. Estuarine ecosystems are under pressure from multiple anthropogenic stressors (e.g. increasing sediment and nutrient loads, pollution, climate change) that are affecting the functions and services these ecosystems provide. Here, we used long-term estuarine benthic invertebrate monitoring data (∼30 year time-series) to evaluate the responses of macrobenthic invertebrate communities and indicator species to climatic, oceanic, freshwater, and local environmental drivers in New Zealand estuaries. We aimed to improve our ability to predict ecosystem change and understand the effects of multiple environment drivers on benthic communities. Our analyses showed that the abundance and richness of macrobenthic fauna and four indicator taxa (bivalves known to have differing tolerances to sediment mud content: Austrovenus stutchburyi, Macomona liliana, Theora lubrica, and Arthritica bifurca) responded to unique combinations of multiple environmental drivers across sites and times. Macrobenthic responses were highly mixed (i.e., positive and negative) and site-dependent. We also show that responses of macrobenthic fauna were lagged and most strongly related to climatic and oceanic drivers. The way the macrobenthos responded has implications for predicting and understanding the ecological consequences of a rapidly changing environment and how we conserve and manage coastal ecosystems.

Responses of the Macroalga Ulva prolifera Müller to Ocean Acidification Revealed by Complementary NMR- and MS-Based Omics Approaches

Ocean acidification (OA) is a dramatic perturbation of seawater environments due to increasing anthropogenic emissions of CO₂. Several studies indicated that OA frequently induces marine biota stress and a reduction of biodiversity. Here, we adopted the macroalga Ulva prolifera as a model and applied a complementary multi-omics approach to investigate the metabolic profiles under normal and acidified conditions. Our results show that U. prolifera grows at higher rates in acidified environments. Consistently, we observed lower sucrose and phosphocreatine concentrations in response to a higher demand of energy for growth and a higher availability of essential amino acids, likely related to increased protein biosynthesis. In addition, pathways leading to signaling and deterrent compounds appeared perturbed. Finally, a remarkable shift was observed here for the first time in the fatty acid composition of triglycerides, with a decrease in the relative abundance of PUFAs towards an appreciable increase of palmitic acid, thus suggesting a remodeling in lipid biosynthesis. Overall, our studies revealed modulation of several biosynthetic pathways under OA conditions in which, besides the possible effects on the marine ecosystem, the metabolic changes of the alga should be taken into account considering its potential nutraceutical applications.

Structure-Function Relationships of Oxygen Transport Proteins in Marine Invertebrates Enduring Higher Temperatures and Deoxygenation

AbstractPredictions for climate change-to lesser and greater extents-reveal a common scenario in which marine waters are characterized by a deadly trio of stressors: higher temperatures, lower oxygen levels, and acidification. Ectothermic taxa that inhabit coastal waters, such as shellfish, are vulnerable to rapid and prolonged environmental disturbances, such as heatwaves, pollution-induced eutrophication, and dysoxia. Oxygen transport capacity of the hemolymph (blood equivalent) is considered the proximal driver of thermotolerance and respiration in many invertebrates. Moreover, maintaining homeostasis under environmental duress is inextricably linked to the activities of the hemolymph-based oxygen transport or binding proteins. Several protein groups fulfill this role in marine invertebrates: copper-based extracellular hemocyanins, iron-based intracellular hemoglobins and hemerythrins, and giant extracellular hemoglobins. In this brief text, we revisit the distribution and multifunctional properties of oxygen transport proteins, notably hemocyanins, in the context of climate change, and the consequent physiological reprogramming of marine invertebrates.

Does pH variation influence the toxicity of organic contaminants in estuarine sediments? Effects of Irgarol on nematode assemblages

Natural pH values in coastal waters vary largely among locations, ecosystems, and time periods; still, there is an ongoing acidification trend. In this scenario, more acidic pH values can alter bioavailability of organic contaminants, to organisms. Despite this, interactive effects between pH and chemical substances are not usually considered in Ecological Risk Assessment protocols. This study investigated the effects of pH on the toxicity of a hydrophobic organic compound on a benthic community using a microcosm experiment setup to assess the response of nematode assemblages exposed to environmentally relevant concentrations of Irgarol at two natural pH conditions. Estuarine nematode assemblages were exposed to two concentrations of Irgarol at pH 7.0 and 8.0 for periods of 7 and 35 days. Lower diversity of nematode genera was observed at the highest tested Irgarol concentration (1281 ± 65 ng.g^-1). The results showed that the effects of Irgarol contamination were independent of pH variation, indicating no influence of acidification within this range on the toxicity of Irgarol to benthic meiofauna. However, the results showed that estuarine nematode assemblages are impacted by long-term exposure to low (but naturally occurring) pHs. This indicates that estuarine organisms may be under naturally high physiological pressure and that permanent changes in the ecosystem's environmental factors, such as future coastal ocean acidification, may drive organisms closer to the edges of their tolerance windows.

Comparative transcriptomics reveals altered species interaction between the bioeroding sponge Cliona varians and the coral Porites furcata under ocean acidification

Bioeroding sponges interact and compete with corals on tropical reefs. Experimental studies have shown global change alters this biotic interaction, often in favor of the sponge. Ocean acidification in particular increases sponge bioerosion and reduces coral calcification, yet little is known about the molecular basis of these changes. We used RNA-Seq data to understand how acidification impacts the interaction between the bioeroding sponge, Cliona varians, and the coral, Porites furcata, at the transcriptomic level. Replicate sponge and coral genets were exposed to ambient (8.1 pH) and acidified (7.6 pH) conditions in isolation and in treatments where they were joined for 48hrs. The coral had a small gene expression response (tens of transcripts) to the sponge, suggesting it does little at the transcriptomic level to deter sponge overgrowth. By contrast, the sponge differentially expressed 7320 transcripts in response to the coral under ambient conditions and 3707 transcripts in response to acidification. Overlap in the responses to acidification and the coral, 2500 transcripts expressed under both treatments, suggests a similar physiological response to both cues. The sponge expressed 50x fewer transcripts in response to the coral under acidification, suggesting energetic costs of bioerosion, and other cellular processes, are lower for sponges under acidification. Our results suggest how acidification drives ecosystem-level changes in the accretion/bioerosion balance on coral reefs. This shift is not only the result of changes to the thermodynamic balance of these chemical reactions but also the result of active physiological responses of organisms to each other and their abiotic environment.

pH Regulates the Formation and Hatching of Cryptocaryon irritans Tomonts, Which Affects Cryptocaryoniasis Occurrence in Larimichthys crocea Aquaculture

Cryptocaryon irritans are the main pathogens of white spot disease in marine teleost. However, the occurrence of cryptocaryoniasis is influenced by several abiotic factors including the pH. To explore the effect of pH on the life cycle of C. irritans (encystment, cleavage, and hatchability), protomonts and tomonts of C. irritans were incubated in seawater of 10 different pH levels (2-11). pH 8 was used as the control. The change in morphology and infectivity of theronts that hatched from tomonts against Larimichthys crocea were then recorded. We found that pH 6-9 had no significant effect on the encystment, cleavage, and hatching of the parasites. However, pH beyond this limit decreased the cleavage and hatching of the tomonts. Furthermore, extreme pH decreased the number of theronts hatched by each tomont and the pathogenicity of the theronts, but increased the aspect ratio of the theronts. Infectivity experiments further revealed that extreme pH significantly decreased the infectivity of C. irritans against L. crocea. In conclusion, the C. irritans can survive in pH of 5 to 10, but pH 6-9 is the optimal range for the reproduction and infectivity of C. irritans. However, extreme pH negatively affects these aspects. IMPORTANCE Cryptocaryon irritans is a ciliate parasite that causes "white spot disease" in marine teleosts. The disease outbreak is influenced by hosts and a range of abiotic factors, such as temperature, salinity, and pH. Studies have shown that change in pH of seawater affects the structure (diversity and abundance of marine organisms) of marine ecosystem. However, how pH affects the life cycle and survival of C. irritans, and how future ocean acidification will affect the occurrence of cryptocaryoniasis, are not well understood. In this study, we explored the effect of pH on the formation and hatching of C. irritans tomonts. The findings of this study provide the foundation of the environmental adaptation of C. irritans, the occurrence of cryptocaryoniasis, and better management of marine fish culture.

Effects of Local Acidification on Benthic Communities at Shallow Hydrothermal Vents of the Aeolian Islands (Southern Tyrrhenian, Mediterranean Sea)

The Aeolian Islands (Mediterranean Sea) host a unique hydrothermal system called the "Smoking Land" due to the presence of over 200 volcanic CO₂-vents, resulting in water acidification phenomena and the creation of an acidified benthic environment. Here, we report the results of a study conducted at three sites located at ca. 16, 40, and 80 m of depth, and characterized by CO₂ emissions to assess the effects of acidification on meio- and macrobenthic assemblages. Acidification caused significant changes in both meio- and macrofaunal assemblages, with a clear decrease in terms of abundance and a shift in community composition. A noticeable reduction in biomass was observed only for macrofauna. The most sensitive meiofaunal taxa were kinorhynchs and turbellarians that disappeared at the CO₂ sites, while the abundance of halacarids and ostracods increased, possibly as a result of the larger food availability and the lower predatory pressures by the sensitive meiofaunal and macrofaunal taxa. Sediment acidification also causes the disappearance of more sensitive macrofaunal taxa, such as gastropods, and the increase in tolerant taxa such as oligochaetes. We conclude that the effects of shallow CO₂-vents result in the progressive simplification of community structure and biodiversity loss due to the disappearance of the most sensitive meio- and macrofaunal taxa.

Physiological responses of the symbiotic shrimp Ancylocaris brevicarpalis and its host sea anemone Stichodactyla haddoni to ocean acidification

In this study, the physiology of symbiotic 'peacock-tail' shrimp Ancylocaris brevicarpalis and its host 'Haddon's carpet' sea anemone Stichodactyla haddoni were tested under lowered pH (7.7) and control (8.1) conditions. The biochemical responses such as digestive enzyme (AP), organic acids (lactate and succinate), oxidative damages (MDA), antioxidants metabolites/enzymes (ASC, GSH, SOD, CAT, APX, GPX, GR, POX, and PHOX), and detoxification enzyme (GST) were measured. The AP showed insignificantly reduced values in both the organisms in lowered pH conditions compared to control indicating the effect of abiotic stress. The hierarchical clustering analysis indicated low MDA in sea anemone can be explained by higher POX, APX, GR, ASC, and GSH levels compared to shrimps. However, the detoxification enzyme GST showed less activity in sea anemones compared to shrimps. The results suggest that A. brevicarpalis and sea anemone S. haddoni may have deleterious effects when exposed to short-term acidification stress.

Climate change scenarios of increased CO2 and temperature affect a coral reef peracarid (Crustacea) community

The effects of applying scenarios of increasing CO₂ and temperature, using a mesocosm experiment, on the structure of a macrofaunal coral reef peracarid community were investigated for the first time. Samples were taken from artificial substrate units (ASUs), colonized by macrofauna from the coral reef subtidal zone of Serrambi beach (Brazil). In the laboratory, the ASUs were exposed to a Control (Ctrl) treatment and three climate change Scenarios (Sc) (increase of T° of 0.6, 2, and 3 °C, and pH drop of 0.1, 0.3, and 0.7 units for Sc I, II and III respectively), and were collected after 15 and 29 days of exposure. Our results showed that the effect of different temperature and acidity levels under experimental climate change scenarios significantly impacted density, diversity and community structure. Major differences were observed when applying Sc II and III. Peracarida also showed a reduction in specimen number when comparing both exposure times. Overall, Amphipoda, Tanaidacea and Isopoda communities all displayed a reduction in the number of individuals for both scenarios and exposure time factors, while Cumacea responded negatively in all scenarios, suggesting that these individuals were more sensitive to the experimental conditions. Dissimilarities were greatest between the Ctrl and Sc III, particularly after 29 days. Two species, Elasmopus longipropodus (Amphipoda) and Chondrochelia dubia (Tanaidacea), greatly contributed to these dissimilarities. This study demonstrates that even an intermediate level of increasing ocean temperature and acidification will negatively impact the structure of the Peracarida macrofaunal community on coral reefs. Also demonstrates that different species of Peracarida exhibit divergent response patterns, highlighting the specific responses of these taxa to the impacts of environmental stressors. These outcomes highlight the importance of studying the effects of climate change on benthic peracarids, especially because they incubate their eggs. This characteristic can reduce migration potential and thereby reduces the individual's ability to disperse in response to a changing environment.

Combined effects of ocean warming and acidification on marine fish and shellfish: A molecule to ecosystem perspective

It is expected that by 2050 human population will exceed nine billion leading to increased pressure on marine ecosystems. Therefore, it is conjectured various levels of ecosystem functioning starting from individual to population-level, species distribution, food webs and trophic interaction dynamics will be severely jeopardized in coming decades. Ocean warming and acidification are two prime threats to marine biota, yet studies about their cumulative effect on marine fish and shellfishes are still in its infancy. This review assesses existing information regarding the interactive effects of global environmental factors like warming and acidification in the perspective of marine capture fisheries and aquaculture industry. As climate change continues, distribution pattern of species is likely to be altered which will impact fisheries and fishing patterns. Our work is an attempt to compile the existing literatures in the biological perspective of the above-mentioned stressors and accentuate a clear outline of knowledge in this subject. We reviewed studies deciphering the biological consequences of warming and acidification on fish and shellfishes in the light of a molecule to ecosystem perspective. Here, for the first time impacts of these two global environmental drivers are discussed in a holistic manner taking into account growth, survival, behavioural response, prey predator dynamics, calcification, biomineralization, reproduction, physiology, thermal tolerance, molecular level responses as well as immune system and disease susceptibility. We suggest urgent focus on more robust, long term, comprehensive and ecologically realistic studies that will significantly contribute to the understanding of organism's response to climate change for sustainable capture fisheries and aquaculture.

Diverse silk and silk-like proteins derived from terrestrial and marine organisms and their applications

Organisms develop unique systems in a given environment. In the process of adaptation, they employ materials in a clever way, which has inspired mankind extensively. Understanding the behavior and material properties of living organisms provides a way to emulate these natural systems and engineer various materials. Silk is a material that has been with human for over 5000 years, and the success of mass production of silkworm silk has realized its applications to medical, pharmaceutical, optical, and even electronic fields. Spider silk, which was characterized later, has expanded the application sectors to textile and military materials based on its tough mechanical properties. Because silk proteins are main components of these materials and there are abundant creatures producing silks that have not been studied, the introduction of new silk proteins would be a breakthrough of engineering materials to open innovative industry fields. Therefore, in this review, we present diverse silk and silk-like proteins and how they are utilized with respect to organism's survival. Here, the range of organisms are not constrained to silkworms and spiders but expanded to other insects, and even marine creatures which produce silk-like proteins that are not observed in terrestrial silks. This viewpoint broadening of silk and silk-like proteins would suggest diverse targets of engineering to design promising silk-based materials. STATEMENT OF SIGNIFICANCE: Silk has been developed as a biomedical material due to unique mechanical and chemical properties. For decades, silks from various silkworm and spider species have been intensively studied. More recently, other silk and silk-like proteins with different sequences and structures have been reported, not only limited to terrestrial organisms (honeybee, green lacewing, caddisfly, and ant), but also from marine creatures (mussel, squid, sea anemone, and pearl oyster). Nevertheless, there has hardly been well-organized literature on silks from such organisms. Regarding the relationship among sequence-structure-properties, this review addresses how silks have been utilized with respect to organism's survival. Finally, this information aims to improve the understanding of diverse silk and silk-like proteins which can offer a significant interest to engineering fields.

Urban Nature: Does Green Infrastructure Relate to the Cultural and Creative Vitality of European Cities?

The COVID-19 pandemic severely upended cultural and creative production, consumption, and interactions in cities. Open green spaces, parks, forests, and gardens—green infrastructure—were instead utilized by citizens as a substitute for stimulating social interactions, sustainable tourism, and green growth. (1) The purpose of this research is to understand whether the availability of green infrastructure relates to the Cultural and Creative Cities Monitor (CCCM) benchmarking project developed by the Joint Research Centre of the European Commission performance. Does new evidence suggest revising the CCCM conceptual framework and related urban policies, especially in relation to the EU Green Deal? (2) Data from OpenStreetMap was used to count the amount of green infrastructure in 184 European Cities covered by the CCM and was then correlated with the sub-indices of the CCCM. (3) We found a moderately positive correlation of green infrastructure with the cultural vibrancy of a city and a weak positive correlation with the enabling environment of a city. (4) In light of the COVID-19 pandemic, the EU Green Deal and several other policy initiatives aimed at urban greening, we recommend that the CCCM include an Urban Nature sub-index as one of the performance indicators of the CCCM. An Urban Nature sub-index will broaden the goal of the CCCM by providing policymakers with a better understanding of actions and strategies to allow culture to contribute to social inclusion and green growth strategies in cities.

Seagrass-driven changes in carbonate chemistry enhance oyster shell growth

Quantifying the strength of non-trophic interactions exerted by foundation species is critical to understanding how natural communities respond to environmental stress. In the case of ocean acidification (OA), submerged marine macrophytes, such as seagrasses, may create local areas of elevated pH due to their capacity to sequester dissolved inorganic carbon through photosynthesis. However, although seagrasses may increase seawater pH during the day, they can also decrease pH at night due to respiration. Therefore, it remains unclear how consequences of such diel fluctuations may unfold for organisms vulnerable to OA. We established mesocosms containing different levels of seagrass biomass (Zostera marina) to create a gradient of carbonate chemistry conditions and explored consequences for growth of juvenile and adult oysters (Crassostrea gigas), a non-native species widely used in aquaculture that can co-occur, and is often grown, in proximity to seagrass beds. In particular, we investigated whether increased diel fluctuations in pH due to seagrass metabolism affected oyster growth. Seagrasses increased daytime pH up to 0.4 units but had little effect on nighttime pH (reductions less than 0.02 units). Thus, both the average pH and the amplitude of diel pH fluctuations increased with greater seagrass biomass. The highest seagrass biomass increased oyster shell growth rate (mm day^-1) up to 40%. Oyster somatic tissue weight and oyster condition index exhibited a different pattern, peaking at intermediate levels of seagrass biomass. This work demonstrates the ability of seagrasses to facilitate oyster calcification and illustrates how non-trophic metabolic interactions can modulate effects of environmental change.

Ervilia castanea (Mollusca, Bivalvia) populations adversely affected at CO2 seeps in the North Atlantic

Sites with naturally high CO₂ conditions provide unique opportunities to forecast the vulnerability of coastal ecosystems to ocean acidification, by studying the biological responses and potential adaptations to this increased environmental variability. In this study, we investigated the bivalve Ervilia castanea in coastal sandy sediments at reference sites and at volcanic CO₂ seeps off the Azores, where the pH of bottom waters ranged from average oceanic levels of 8.2, along gradients, down to 6.81, in carbonated seawater at the seeps. The bivalve population structure changed markedly at the seeps. Large individuals became less abundant as seawater CO₂ levels rose and were completely absent from the most acidified sites. In contrast, small bivalves were most abundant at the CO₂ seeps. We propose that larvae can settle and initially live in high abundances under elevated CO₂ levels, but that high rates of post-settlement dispersal and/or mortality occur. Ervilia castanea were susceptible to elevated CO₂ levels and these effects were consistently associated with lower food supplies. This raises concerns about the effects of ocean acidification on the brood stock of this species and other bivalve molluscs with similar life history traits.

Seawater Acidification Affects Beta-Diversity of Benthic Communities at a Shallow Hydrothermal Vent in a Mediterranean Marine Protected Area (Underwater Archaeological Park of Baia, Naples, Italy)

One of the most important pieces of climate change evidence is ocean acidification. Acidification effects on marine organisms are widely studied, while very little is known regarding its effects on assemblages’ β-diversity. In this framework, shallow hydrothermal vents within a Marine Protected Area (MPA) represent natural ecosystems acting as laboratory set-ups where the continuous carbon dioxide emissions affect assemblages with consequences that can be reasonably comparable to the effects of global water acidification. The aim of the present study is to test the impact of seawater acidification on the β-diversity of soft-bottom assemblages in a shallow vent field located in the Underwater Archeological Park of Baia MPA (Gulf of Naples, Mediterranean Sea). We investigated macro- and meiofauna communities of the ‘Secca delle fumose’ vent system in sites characterized by sulfurous (G) and carbon dioxide emissions (H) that are compared with control/inactive sites (CN and CS). Statistical analyses were performed on the most represented macrobenthic (Mollusca, Polychaeta, and Crustacea), and meiobenthic (Nematoda) taxa. Results show that the lowest synecological values are detected at H and, to a lesser extent, at G. Multivariate analyses show significant differences between hydrothermal vents (G, H) and control/inactive sites; the highest small-scale heterogeneities (measure of β-diversity) are detected at sites H and G and are mainly affected by pH, TOC (Total Organic Carbon), and cations concentrations. Such findings are probably related to acidification effects, since MPA excludes anthropic impacts. In particular, acidification markedly affects β-diversity and an increase in heterogeneity among sample replicates coupled to a decrease in number of taxa is an indicator of redundancy loss and, thus, of resilience capacity. The survival is assured to either tolerant species or those opportunistic taxa that can find good environmental conditions among gravels of sand.

Thermal plasticity is independent of environmental history in an intertidal seaweed

Organisms inhabiting the intertidal zone have been used to study natural ecophysiological responses and adaptations to thermal stress because these organisms are routinely exposed to high-temperature conditions for hours at a time. While intertidal organisms may be inherently better at withstanding temperature stress due to regular exposure and acclimation, they could be more vulnerable to temperature stress, already living near the edge of their thermal limits. Strong gradients in thermal stress across the intertidal zone present an opportunity to test whether thermal tolerance is a plastic or canalized trait in intertidal organisms. Here, we studied the intertidal pool-dwelling calcified alga, Ellisolandia elongata, under near-future temperature regimes, and the dependence of its thermal acclimatization response on environmental history. Two timescales of environmental history were tested during this experiment. The intertidal pool of origin was representative of long-term environmental history over the alga's life (including settlement and development), while the pool it was transplanted into accounted for recent environmental history (acclimation over many months). Unexpectedly, neither long-term nor short-term environmental history, nor ambient conditions, affected photosynthetic rates in E. elongata. Individuals were plastic in their photosynthetic response to laboratory temperature treatments (mean 13.2°C, 15.7°C, and 17.7°C). Further, replicate ramets from the same individual were not always consistent in their photosynthetic performance from one experimental time point to another or between treatments and exhibited no clear trend in variability over experimental time. High variability in climate change responses between individuals may indicate the potential for resilience to future conditions and, thus, may play a compensatory role at the population or species level over time.

Future ocean climate homogenizes communities across habitats through diversity loss and rise of generalist species

Predictions of the effects of global change on ecological communities are largely based on single habitats. Yet in nature, habitats are interconnected through the exchange of energy and organisms, and the responses of local communities may not extend to emerging community networks (i.e., metacommunities). Using large mesocosms and meiofauna communities as a model system, we investigated the interactive effects of ocean warming and acidification on the structure of marine metacommunities from three shallow-water habitats: sandy soft-bottoms, marine vegetation, and rocky reef substrates. Primary producers and detritus-key food sources for meiofauna-increased in biomass under the combined effect of temperature and acidification. The enhanced bottom-up forcing boosted nematode densities but impoverished the functional and trophic diversity of nematode metacommunities. The combined climate stressors further homogenized meiofauna communities across habitats. Under present-day conditions metacommunities were structured by habitat type, but under future conditions they showed an unstructured random pattern with fast-growing generalist species dominating the communities of all habitats. Homogenization was likely driven by local species extinctions, reducing interspecific competition that otherwise could have prevented single species from dominating multiple niches. Our findings reveal that climate change may simplify metacommunity structure and prompt biodiversity loss, which may affect the biological organization and resilience of marine communities.

Effects of reduced seawater pH on nematode community composition and diversity in sandy sediments

The present study investigated the potential effects of seawater acidification on the taxonomic structure and diversity of nematode communities using a microcosm experiment. Nematode samples for the microcosm experiment were collected from the low tidal zone of two sandy beaches with different sediment compositions (medium sand vs. very fine sand) in Qingdao (China). In the microcosm, nematode communities were exposed to nine experimental treatments comprising two pH levels for 56 days: 8.0 (ambient control) and 7.3. Communities were exposed for 0, 7, 14, 28, or 56 days. Results showed that the most distinguishable differences in nematode community structure and diversity indices were caused by sediment type. Reduced pH changed the taxonomic structure of nematode communities in medium sand sediments. An increase in species with higher tolerance to lowered pH occurred as a response and resulted in increased diversity in medium sand sediments. Nematode communities in finer sediments appeared less sensitive to reduced pH.

Long-term changes in the structure of benthic communities: Revisiting a sampling transect in Crete after 24 years

A bathymetric transect in the north coast of Crete first studied in 1989, was revisited 24 years later. Identical sampling design, season, techniques and protocols were followed in both studies in order to minimize bias in the long-term comparisons. This comprehensive macrofaunal dataset (4 stations, 2 sampling seasons, 7 replicates in each study) revealed changes in benthic diversity and community composition between the sampling periods. The recorded changes were higher at the stations located close to the coastal zone. In addition, while benthic communities showed lower total abundance during the recent sampling period, species abundances were more evenly distributed indicating that some species dominated the historical communities. In spite of these changes, the ecological status remained above the threshold values for good ecological status. The results indicated that changes in the benthic community seem to have been driven by local anthropogenic factors and natural variability rather than by large-scale factors such as nutrients influxes in the entire Mediterranean Basin.

Effects of short-term and long-term exposure to ocean acidification on carbonic anhydrase activity and morphometric characteristics in the invasive polychaete Branchiomma boholense (Annelida: Sabellidae): A case-study from a CO2 vent system

The aim of this study was to test the effects of short- and long-term exposure to high pCO₂ on the invasive polychaete Branchiomma boholense (Grube, 1878), (Sabellidae), through the implementation of a transplant experiment at the CO₂ vents of the Castello Aragonese at the island of Ischia (Italy). Analysis of carbonic anhydrase (CA) activity, protein tissue content and morphometric characteristics were performed on transplanted individuals (short-term exposure) as well as on specimens resident to both normal and low pH/high pCO₂ environments (long-term exposure). Results obtained on transplanted worms showed no significant differences in CA activity between individuals exposed to control and acidified conditions, while a decrease in weight was observed under short-term acclimatization to both control and low pH, although at low pH the decrease was more pronounced (∼20%). As regard individuals living under chronic exposure to high pCO₂, the morphometric results revealed a significantly lower (70%) wet weight of specimens from the vents with respect to animals living in high pH/low pCO₂ areas. Moreover, individuals living in the Castello vents showed doubled values of enzymatic activity and a significantly higher (50%) protein tissue content compared to specimens native from normal pH/low pCO₂. The results of this study demonstrated that B. boholense is inclined to maintain a great homeostatic capacity when exposed to low pH, although likely at the energetic expense of other physiological processes such as growth, especially under chronic exposure to high pCO₂.

CO2 leakage can cause loss of benthic biodiversity in submarine sands

One of the options to mitigate atmospheric CO₂ increase is CO₂ Capture and Storage in sub-seabed geological formations. Since predicting long-term storage security is difficult, different CO₂ leakage scenarios and impacts on marine ecosystems require evaluation. Submarine CO₂ vents may serve as natural analogues and allow studying the effects of CO₂ leakage in a holistic approach. At the study site east of Basiluzzo Islet off Panarea Island (Italy), gas emissions (90-99% CO₂) occur at moderate flows (80-120 L m^-2 h^-1). We investigated the effects of acidified porewater conditions (pH_T range: 5.5-7.7) on the diversity of benthic bacteria and invertebrates by sampling natural sediments in three subsequent years and by performing a transplantation experiment with a duration of one year, respectively. Both multiple years and one year of exposure to acidified porewater conditions reduced the number of benthic bacterial operational taxonomic units and invertebrate species diversity by 30-80%. Reduced biodiversity at the vent sites increased the temporal variability in bacterial and nematode community biomass, abundance and composition. While the release from CO₂ exposure resulted in a full recovery of nematode species diversity within one year, bacterial diversity remained affected. Overall our findings showed that seawater acidification, induced by seafloor CO₂ emissions, was responsible for loss of diversity across different size-classes of benthic organisms, which reduced community stability with potential relapses on ecosystem resilience.

Marine Metazoan Modern Mass Extinction: Improving Predictions by Integrating Fossil, Modern, and Physiological Data

Evolution, extinction, and dispersion are fundamental processes affecting marine biodiversity. Until recently, studies of extant marine systems focused mainly on evolution and dispersion, with extinction receiving less attention. Past extinction events have, however, helped shape the evolutionary history of marine ecosystems, with ecological and evolutionary legacies still evident in modern seas. Current anthropogenic global changes increase extinction risk and pose a significant threat to marine ecosystems, which are critical for human use and sustenance. The evaluation of these threats and the likely responses of marine ecosystems requires a better understanding of evolutionary processes that affect marine ecosystems under global change. Here, we discuss how knowledge of ( a) changes in biodiversity of ancient marine ecosystems to past extinctions events, ( b) the patterns of sensitivity and biodiversity loss in modern marine taxa, and ( c) the physiological mechanisms underpinning species' sensitivity to global change can be exploited and integrated to advance our critical thinking in this area.

The absence of the pCO2 effect on dissolved 134Cs uptake in select marine organisms

Ocean acidification have been shown to not affect the capacity of bivalves to bioaccumulation ¹³⁴Cs in their tissue; but as this was studied on only one species to date. There is therefore a need to verify if this holds true for other bivalve species or other marine invertebrates. The present short communication confirms that in the scallop Mimachlamys varia and the prawn Penaeus japonicus, two species that supposedly have a record to preferentially concentrates this radionuclide, that bioconcentration of ¹³⁴Cs was shown not to be influenced by a decreasing pH (and thereby increasing seawater pCO₂). Although the dissolved ¹³⁴Cs was taken up in a similar manner under different pH values (8.1, 7.8, and 7.5) in both species, being described by a saturation state equilibrium model, the species displayed different bioconcentration capacities of ¹³⁴Cs: CF_ss in the prawns was approximately 10-fold higher than in scallops. Such results suggest that the Cs bioconcentration capacity are mainly dependent of the taxa and that uptake processes are independent the physiological ones involved in the biological responses of prawns and scallops to ocean acidification.

A comparative analysis of metabarcoding and morphology-based identification of benthic communities across different regional seas

In a world of declining biodiversity, monitoring is becoming crucial. Molecular methods, such as metabarcoding, have the potential to rapidly expand our knowledge of biodiversity, supporting assessment, management, and conservation. In the marine environment, where hard substrata are more difficult to access than soft bottoms for quantitative ecological studies, Artificial Substrate Units (ASUs) allow for standardized sampling. We deployed ASUs within five regional seas (Baltic Sea, Northeast Atlantic Ocean, Mediterranean Sea, Black Sea, and Red Sea) for 12-26 months to measure the diversity and community composition of macroinvertebrates. We identified invertebrates using a traditional approach based on morphological characters, and by metabarcoding of the mitochondrial cytochrome oxidase I (COI) gene. We compared community composition and diversity metrics obtained using the two methods. Diversity was significantly correlated between data types. Metabarcoding of ASUs allowed for robust comparisons of community composition and diversity, but not all groups were successfully sequenced. All locations were significantly different in taxonomic composition as measured with both kinds of data. We recovered previously known regional biogeographical patterns in both datasets (e.g., low species diversity in the Black and Baltic Seas, affinity between the Bay of Biscay and the Mediterranean). We conclude that the two approaches provide complementary information and that metabarcoding shows great promise for marine monitoring. However, until its pitfalls are addressed, the use of metabarcoding in monitoring of rocky benthic assemblages should be used in addition to classical approaches rather than instead of them.

Decalcification and survival of benthic foraminifera under the combined impacts of varying pH and salinity

Coastal areas display natural large environmental variability such as frequent changes in salinity, pH, and carbonate chemistry. Anthropogenic impacts - especially ocean acidification - increase this variability, which may affect the living conditions of coastal species, particularly, calcifiers. We performed culture experiments on living benthic foraminifera to study the combined effects of lowered pH and salinity on the calcification abilities and survival of the coastal, calcitic species Ammonia sp. and Elphidium crispum. We found that in open ocean conditions (salinity ∼35) and lower pH than usual values for these species, the specimens displayed resistance to shell (test) dissolution for a longer time than in brackish conditions (salinity ∼5 to 20). However, the response was species specific as Ammonia sp. specimens survived longer than E. crispum specimens when placed in the same conditions of salinity and pH. Living, decalcified juveniles of Ammonia sp. were observed and we show that desalination is one cause for the decalcification. Finally, we highlight the ability of foraminifera to survive under Ω_calc < 1, and that high salinity and [Ca²⁺] as building blocks are crucial for the foraminiferal calcification process.

Experimental strategies to assess the biological ramifications of multiple drivers of global ocean change-A review

Marine life is controlled by multiple physical and chemical drivers and by diverse ecological processes. Many of these oceanic properties are being altered by climate change and other anthropogenic pressures. Hence, identifying the influences of multifaceted ocean change, from local to global scales, is a complex task. To guide policy-making and make projections of the future of the marine biosphere, it is essential to understand biological responses at physiological, evolutionary and ecological levels. Here, we contrast and compare different approaches to multiple driver experiments that aim to elucidate biological responses to a complex matrix of ocean global change. We present the benefits and the challenges of each approach with a focus on marine research, and guidelines to navigate through these different categories to help identify strategies that might best address research questions in fundamental physiology, experimental evolutionary biology and community ecology. Our review reveals that the field of multiple driver research is being pulled in complementary directions: the need for reductionist approaches to obtain process-oriented, mechanistic understanding and a requirement to quantify responses to projected future scenarios of ocean change. We conclude the review with recommendations on how best to align different experimental approaches to contribute fundamental information needed for science-based policy formulation.

Impact of ocean acidification and warming on the productivity of a rock pool community

This study examined experimentally the combined effect of ocean acidification and warming on the productivity of rock pool multi-specific assemblages, composed of coralline algae, fleshy algae, and grazers. Natural rock pool communities experience high environmental fluctuations. This may confer physiological advantage to rock pool communities when facing predicted acidification and warming. The effect of ocean acidification and warming have been assessed at both individual and assemblage level to examine the importance of species interactions in the response of assemblages. We hypothesized that rock pool assemblages have physiological advantage when facing predicted ocean acidification and warming. Species exhibited species-specific responses to increased temperature and pCO₂. Increased temperature and pCO₂ have no effect on assemblage photosynthesis, which was mostly influenced by fleshy algal primary production. The response of coralline algae to ocean acidification and warming depended on the season, which evidenced the importance of physiological adaptations to their environment in their response to climate change. We suggest that rock pool assemblages are relatively robust to changes in temperature and pCO₂, in terms of primary production.

Effects of sub-seabed CO2 leakage: Short- and medium-term responses of benthic macrofaunal assemblages

The continued rise in atmospheric carbon dioxide (CO₂) levels is driving climate change and temperature shifts at a global scale. CO₂ Capture and Storage (CCS) technologies have been suggested as a feasible option for reducing CO₂ emissions and mitigating their effects. However, before CCS can be employed at an industrial scale, any environmental risks associated with this activity should be identified and quantified. Significant leakage of CO₂ from CCS reservoirs and pipelines is considered to be unlikely, however direct and/or indirect effects of CO₂ leakage on marine life and ecosystem functioning must be assessed, with particular consideration given to spatial (e.g. distance from the source) and temporal (e.g. duration) scales at which leakage impacts could occur. In the current mesocosm experiment we tested the potential effects of CO₂ leakage on macrobenthic assemblages by exposing infaunal sediment communities to different levels of CO₂ concentration (400, 1000, 2000, 10,000 and 20,000 ppm CO₂), simulating a gradient of distance from a hypothetic leakage, over short-term (a few weeks) and medium-term (several months). A significant impact on community structure, abundance and species richness of macrofauna was observed in the short-term exposure. Individual taxa showed idiosyncratic responses to acidification. We conclude that the main impact of CO₂ leakage on macrofaunal assemblages occurs almost exclusively at the higher CO₂ concentration and over short time periods, tending to fade and disappear at increasing distance and exposure time. Although under the cautious perspective required by the possible context-dependency of the present findings, this study contributes to the cost-benefit analysis (environmental risk versus the achievement of the intended objectives) of CCS strategies.

Community responses to seawater warming are conserved across diverse biological groupings and taxonomic resolutions

Temperature variability is a major driver of ecological pattern, with recent changes in average and extreme temperatures having significant impacts on populations, communities and ecosystems. In the marine realm, very few experiments have manipulated temperature in situ, and current understanding of temperature effects on community dynamics is limited. We developed new technology for precise seawater temperature control to examine warming effects on communities of bacteria, microbial eukaryotes (protists) and metazoans. Despite highly contrasting phylogenies, size spectra and diversity levels, the three community types responded similarly to seawater warming treatments of +3°C and +5°C, highlighting the critical and overarching importance of temperature in structuring communities. Temperature effects were detectable at coarse taxonomic resolutions and many taxa responded positively to warming, leading to increased abundances at the community-level. Novel field-based experimental approaches are essential to improve mechanistic understanding of how ocean warming will alter the structure and functioning of diverse marine communities.

CO2 leakage alters biogeochemical and ecological functions of submarine sands

Subseabed CO2 storage is considered a future climate change mitigation technology. We investigated the ecological consequences of CO2 leakage for a marine benthic ecosystem. For the first time with a multidisciplinary integrated study, we tested hypotheses derived from a meta-analysis of previous experimental and in situ high-CO2 impact studies. For this, we compared ecological functions of naturally CO2-vented seafloor off the Mediterranean island Panarea (Tyrrhenian Sea, Italy) to those of nonvented sands, with a focus on biogeochemical processes and microbial and faunal community composition. High CO2 fluxes (up to 4 to 7 mol CO2 m-2 hour-1) dissolved all sedimentary carbonate, and comigration of silicate and iron led to local increases of microphytobenthos productivity (+450%) and standing stocks (+300%). Despite the higher food availability, faunal biomass (-80%) and trophic diversity were substantially lower compared to those at the reference site. Bacterial communities were also structurally and functionally affected, most notably in the composition of heterotrophs and microbial sulfate reduction rates (-90%). The observed ecological effects of CO2 leakage on submarine sands were reproduced with medium-term transplant experiments. This study assesses indicators of environmental impact by CO2 leakage and finds that community compositions and important ecological functions are permanently altered under high CO2.

Combined, short-term exposure to reduced seawater pH and elevated temperature induces community shifts in an intertidal meiobenthic assemblage

In future global change scenarios the surface ocean will experience continuous acidification and rising temperatures. While effects of both stressors on marine, benthic communities are fairly well studied, consequences of the interaction of both factors remain largely unknown. We performed a short-term microcosm experiment exposing a soft-bottom community from an intertidal flat in the Westerscheldt estuary to two levels of seawater pH (ambient pH_T = 7.9, reduced pH_T = 7.5) and temperature (10 °C ambient and 13 °C elevated temperature) in a crossed design. After 8 weeks, meiobenthic community structure and nematode staining ratios, as a proxy for mortality, were compared between treatments and structural changes were related to the prevailing abiotic conditions in the respective treatments (pore water pH_T, sediment grain size, total organic matter content, total organic carbon and nitrogen content, phytopigment concentrations and carbonate concentration). Pore water pH_T profiles were significantly altered by pH and temperature manipulations and the combination of elevated temperature and reduced pH intensified the already more acidic porewater below the oxic zone. Meiofauna community composition was significantly affected by the combination of reduced pH and elevated temperature resulting in increased densities of predatory Platyhelminthes, reduced densities of Copepoda and Nauplii and complete absence of Gastrotricha compared to the experimental control. Furthermore, nematode staining ratio was elevated when seawater pH was reduced pointing towards reduced degradation rates of dead nematode bodies. The observed synergistic interactions of pH and temperature on meiobenthic communities and abiotic sediment characteristics underline the importance of multistressor experiments when addressing impacts of global change on the marine environment.

Natural acidification changes the timing and rate of succession, alters community structure, and increases homogeneity in marine biofouling communities

Ocean acidification may have far-reaching consequences for marine community and ecosystem dynamics, but its full impacts remain poorly understood due to the difficulty of manipulating pCO₂ at the ecosystem level to mimic realistic fluctuations that occur on a number of different timescales. It is especially unclear how quickly communities at various stages of development respond to intermediate-scale pCO₂ change and, if high pCO₂ is relieved mid-succession, whether past acidification effects persist, are reversed by alleviation of pCO₂ stress, or are worsened by departures from prior high pCO₂ conditions to which organisms had acclimatized. Here, we used reciprocal transplant experiments along a shallow water volcanic pCO₂ gradient to assess the importance of the timing and duration of high pCO₂ exposure (i.e., discrete events at different stages of successional development vs. continuous exposure) on patterns of colonization and succession in a benthic fouling community. We show that succession at the acidified site was initially delayed (less community change by 8 weeks) but then caught up over the next 4 weeks. These changes in succession led to homogenization of communities maintained in or transplanted to acidified conditions, and altered community structure in ways that reflected both short- and longer-term acidification history. These community shifts are likely a result of interspecific variability in response to increased pCO₂ and changes in species interactions. High pCO₂ altered biofilm development, allowing serpulids to do best at the acidified site by the end of the experiment, although early (pretransplant) negative effects of pCO₂ on recruitment of these worms were still detectable. The ascidians Diplosoma sp. and Botryllus sp. settled later and were more tolerant to acidification. Overall, transient and persistent acidification-driven changes in the biofouling community, via both past and more recent exposure, could have important implications for ecosystem function and food web dynamics.

Altered sediment biota and lagoon habitat carbonate dynamics due to sea cucumber bioturbation in a high-pCO2 environment

The effects of global change on biological systems and functioning are already measurable, but how ecological interactions are being altered is poorly understood. Ecosystem resilience is strengthened by ecological functionality, which depends on trophic interactions between key species and resilience generated through biogenic buffering. Climate-driven alterations to coral reef metabolism, structural complexity and biodiversity are well documented, but the feedbacks between ocean change and trophic interactions of non-coral invertebrates are understudied. Sea cucumbers, some of the largest benthic inhabitants of tropical lagoon systems, can influence diel changes in reef carbonate dynamics. Whether they have the potential to exacerbate or buffer ocean acidification over diel cycles depends on their relative production of total alkalinity (A_T ) through the dissolution of ingested calcium carbonate (CaCO₃ ) sediments and release of dissolved inorganic carbon (C_T ) through respiration and trophic interactions. In this study, the potential for the sea cucumber, Stichopus herrmanni, a bêche-de-mer (fished) species listed as vulnerable to extinction, to buffer the impacts of ocean acidification on reef carbonate chemistry was investigated in lagoon sediment mesocosms across diel cycles. Stichopus herrmanni directly reduced the abundance of meiofauna and benthic primary producers through its deposit-feeding activity under present-day and near-future pCO₂ . These changes in benthic community structure, as well as A_T (sediment dissolution) and C_T (respiration) production by S. herrmanni, played a significant role in modifying seawater carbonate dynamics night and day. This previously unappreciated role of tropical sea cucumbers, in support of ecosystem resilience in the face of global change, is an important consideration with respect to the bêche-de-mer trade to ensure sea cucumber populations are sustained in a future ocean.

New climatic targets against global warming: will the maximum 2 °C temperature rise affect estuarine benthic communities?

The Paris Agreement signed by 195 countries in 2015 sets out a global action plan to avoid dangerous climate change by limiting global warming to remain below 2 °C. Under that premise, in situ experiments were run to test the effects of 2 °C temperature increase on the benthic communities in a seagrass bed and adjacent bare sediment, from a temperate European estuary. Temperature was artificially increased in situ and diversity and ecosystem functioning components measured after 10 and 30 days. Despite some warmness effects on the analysed components, significant impacts were not verified on macro and microfauna structure, bioturbation or in the fluxes of nutrients. The effect of site/habitat seemed more important than the effects of the warmness, with the seagrass habitat providing more homogenous results and being less impacted by warmness than the adjacent bare sediment. The results reinforce that most ecological responses to global changes are context dependent and that ecosystem stability depends not only on biological diversity but also on the availability of different habitats and niches, highlighting the role of coastal wetlands. In the context of the Paris Agreement it seems that estuarine benthic ecosystems will be able to cope if global warming remains below 2 °C.

Vulnerability of macronutrients to the concurrent effects of enhanced temperature and atmospheric pCO2 in representative shelf sea sediment habitats

Fundamental changes in seawater carbonate chemistry and sea surface temperatures associated with the ocean uptake of anthropogenic CO2 are accelerating, but investigations of the susceptibility of biogeochemical processes to the simultaneous occurrence of multiple components of climate change are uncommon. Here, we quantify how concurrent changes in enhanced temperature and atmospheric pCO2, coupled with an associated shift in macrofaunal community structure and behavior (sediment particle reworking and bioirrigation), modify net carbon and nutrient concentrations (NH4-N, NOx-N, PO4-P) in representative shelf sea sediment habitats (mud, sandy-mud, muddy-sand and sand) of the Celtic Sea. We show that net concentrations of organic carbon, nitrogen and phosphate are, irrespective of sediment type, largely unaffected by a simultaneous increase in temperature and atmospheric pCO2. However, our analyses also reveal that a reduction in macrofaunal species richness and total abundance occurs under future environmental conditions, varies across a gradient of cohesive to non-cohesive sediments, and negatively moderates biogeochemical processes, in particular nitrification. Our findings indicate that future environmental conditions are unlikely to have strong direct effects on biogeochemical processes but, particularly in muddy sands, the abundance, activity, composition and functional role of invertebrate communities are likely to be altered in ways that will be sufficient to regulate the function of the microbial community and the availability of nutrients in shelf sea waters.

Density mediates grasshopper performance in response to temperature manipulation and spider predation in tallgrass prairie

Species interactions are often context-dependent, where outcomes require an understanding of influences among multiple biotic and abiotic factors. However, it remains unclear how abiotic factors such as temperature combine with important biotic factors such as density-dependent food limitation and predation to influence species interactions. Using a native grassland - grasshopper - wolf spider model food chain in tallgrass prairie, we conducted a manipulative field experiment to examine how predator-prey interactions respond to manipulations of temperature, grasshopper density, and food chain length. We find that grasshopper performance responses to temperature and predator treatments were density dependent. At high densities, grasshopper survival decreased with increased temperature when no spiders were present. When spiders were present, grasshopper survival was reduced, and this effect was strongest in the cooled treatment. In contrast, grasshopper survival did not vary significantly with spider presence or among temperature treatments at low grasshopper densities. Our results indicate that context-dependent species interactions are common and highlight the importance of understanding how and when key biotic and abiotic factors combine to influence species interactions.

Effects of elevated carbon dioxide and temperature on locomotion and the repeatability of lateralization in a keystone marine mollusc

Recent work has shown that the behaviour of marine organisms can be affected by elevated PCO2, although little is known about the effect of multiple stressors. We therefore investigated the effect of elevated PCO2 and temperature on locomotion and behaviour during prey searching in the marine gastropod Concholepas concholepas, a predator characteristic of the southeastern Pacific coast. Movement duration, decision time, route finding and lateralization were measured using a T-maze tank with a prey positioned behind a barrier. Four treatments, representing present day and near-future scenarios of ocean acidification and warming were used in rearing the individuals for 6 months. Regardless of the treatment, no significant differences were found in relative and absolute lateralization before and after exposure for 6 months. However, relative lateralization was not repeatable for animals tested after 6 months at elevated PCO2 at both experimental temperatures, whereas it was repeatable in individuals kept at the present day level of PCO2. We suggest that these effects may be related to a behavioural malfunction caused by elevated PCO2. Movement duration, decision time and route finding were not repeatable. However, movement duration and decision time increased and route finding decreased in elevated PCO2 (at 15°C), suggesting that elevated PCO2 has negative effects on the locomotor and sensory performance of C. concholepas in the presence of a prey odour, thereby decreasing their ability to forage efficiently.

CO2 leaking from sub-seabed storage: Responses of two marine bacteria strains

Carbon capture and storage (CCS) in stable geological locations is one of the options to mitigate the negative effects of global warming produced by the increase in CO2 concentrations in the atmosphere. A CO2 leak is one of the risks associated with this strategy. Marine bacteria attached to the sediment may be affected by an acidification event. Responses of two marine strains (Roseobacter sp. CECT 7117 and Pseudomonas litoralis CECT 7670) were assessed under different scenarios using a range of pH values (7.8, 7, 6.5, 6, and 5.5) to mimic a CO2 leak. A CO2 injection system was used to simulate an escape from a stable sub-seabed. Growth rate (μ), cell number, inhibition of Relative Inhibitory Effect (RI CO2) and inhibited population were analysed as endpoints. P. litoralis showed more sensitivity to high CO2 concentrations than Roseobacter sp. Our results highlight the diversity and resistance in marine bacteria and their capacity to adapt under a stressful CO2 leakage.

Simulated leakage of high pCO2 water negatively impacts bivalve dominated infaunal communities from the Western Baltic Sea

Carbon capture and storage is promoted as a mitigation method counteracting the increase of atmospheric CO₂ levels. However, at this stage, environmental consequences of potential CO₂ leakage from sub-seabed storage sites are still largely unknown. In a 3-month-long mesocosm experiment, this study assessed the impact of elevated pCO₂ levels (1,500 to 24,400 μatm) on Cerastoderma edule dominated benthic communities from the Baltic Sea. Mortality of C. edule was significantly increased in the highest treatment (24,400 μatm) and exceeded 50%. Furthermore, mortality of small size classes (0–1 cm) was significantly increased in treatment levels ≥6,600 μatm. First signs of external shell dissolution became visible at ≥1,500 μatm, holes were observed at >6,600 μatm. C. edule body condition decreased significantly at all treatment levels (1,500–24,400 μatm). Dominant meiofauna taxa remained unaffected in abundance. Densities of calcifying meiofauna taxa (i.e. Gastropoda and Ostracoda) decreased in high CO₂ treatments (>6,600 μatm), while the non - calcifying Gastrotricha significantly increased in abundance at 24,400 μatm. In addition, microbial community composition was altered at the highest pCO₂ level. We conclude that strong CO₂ leakage can alter benthic infauna community composition at multiple trophic levels, likely due to high mortality of the dominant macrofauna species C. edule.

Warming and Elevated CO2 Interact to Drive Rapid Shifts in Marine Community Production

Predicting the outcome of future climate change requires an understanding of how alterations in multiple environmental factors manifest in natural communities and affect ecosystem functioning. We conducted an in situ, fully factorial field manipulation of CO₂ and temperature on a rocky shoreline in southeastern Alaska, USA. Warming strongly impacted functioning of tide pool systems within one month, with the rate of net community production (NCP) more than doubling in warmed pools under ambient CO₂ levels relative to initial NCP values. However, in pools with added CO₂, NCP was unaffected by warming. Productivity responses paralleled changes in the carbon-to-nitrogen ratio of a red alga, the most abundant primary producer species in the system, highlighting the direct link between physiology and ecosystem functioning. These observed changes in algal physiology and community productivity in response to our manipulations indicate the potential for natural systems to shift rapidly in response to changing climatic conditions and for multiple environmental factors to act antagonistically.

Ocean acidification through the lens of ecological theory

Ocean acidification, chemical changes to the carbonate system of seawater, is emerging as a key environmental challenge accompanying global warming and other human-induced perturbations. Considerable research seeks to define the scope and character of potential outcomes from this phenomenon, but a crucial impediment persists. Ecological theory, despite its power and utility, has been only peripherally applied to the problem. Here we sketch in broad strokes several areas where fundamental principles of ecology have the capacity to generate insight into ocean acidification's consequences. We focus on conceptual models that, when considered in the context of acidification, yield explicit predictions regarding a spectrum of population- and community-level effects, from narrowing of species ranges and shifts in patterns of demographic connectivity, to modified consumer-resource relationships, to ascendance of weedy taxa and loss of species diversity. Although our coverage represents only a small fraction of the breadth of possible insights achievable from the application of theory, our hope is that this initial foray will spur expanded efforts to blend experiments with theoretical approaches. The result promises to be a deeper and more nuanced understanding of ocean acidification'and the ecological changes it portends.

Alterations in the macrobenthic fauna from Guadarranque River (Southern Spain) associated with sediment-seawater acidification deriving from CO2 leakage

Nowadays, Carbon Storage in Sub-Seabed Geological Structures (CS-SSGS) is having much interest. Nonetheless, these technologies are still under development, especially the leakage of the stored CO2 and the consequent acidification of the environment. Therefore, the goal of this study is to test the impact of CO2-induced acidification on a macrobenthic community due to leakages from CS-SSGS using a mesocosm-based experiment. Results confirmed the significant correlation between the abundance of the species and the pH (positively), and the alkalinity (negatively). Additionally, the BIOENV analysis showed that the majority of the variability in the abundance of the total species was explained for the alkalinity. The correlation analysis showed differential vulnerabilities of different species, especially Cyathura carinata and a non-calcifier species as Hediste diversicolor. Nevertheless, these results showed the importance of taking into account the indirect effect associated with acidification processes, as metal release from sediment.

Force majeure: Will climate change affect our ability to attain Good Environmental Status for marine biodiversity?

The EU Marine Strategy Framework Directive (MSFD) requires that Good Environmental Status (GEnS), is achieved for European seas by 2020. These may deviate from GEnS, its 11 Descriptors, targets and baselines, due to endogenic managed pressures (from activities within an area) and externally due to exogenic unmanaged pressures (e.g. climate change). Conceptual models detail the likely or perceived changes expected on marine biodiversity and GEnS Descriptors in the light of climate change. We emphasise that marine management has to accommodate 'shifting baselines' caused by climate change particularly during GEnS monitoring, assessment and management and 'unbounded boundaries' given the migration and dispersal of highly-mobile species. We suggest climate change may prevent GEnS being met, but Member States may rebut legal challenges by claiming that this is outside its control, force majeure or due to 'natural causes' (Article 14 of the MSFD). The analysis is relevant to management of other global seas.

Acidification effects on biofouling communities: winners and losers

How ocean acidification affects marine life is a major concern for science and society. However, its impacts on encrusting biofouling communities, that are both the initial colonizers of hard substrata and of great economic importance, are almost unknown. We showed that community composition changed significantly, from 92% spirorbids, 3% ascidians and 4% sponges initially to 47% spirorbids, 23% ascidians and 29% sponges after 100 days in acidified conditions (pH 7.7). In low pH, numbers of the spirorbid Neodexiospira pseudocorrugata were reduced ×5 compared to controls. The two ascidians present behaved differently with Aplidium sp. decreasing ×10 in pH 7.7, whereas Molgula sp. numbers were ×4 higher in low pH than controls. Calcareous sponge (Leucosolenia sp.) numbers increased ×2.5 in pH 7.7 over controls. The diatom and filamentous algal community was also more poorly developed in the low pH treatments compared to controls. Colonization of new surfaces likewise showed large decreases in spirorbid numbers, but numbers of sponges and Molgula sp. increased. Spirorbid losses appeared due to both recruitment failure and loss of existing tubes. Spirorbid tubes are comprised of a loose prismatic fabric of calcite crystals. Loss of tube materials appeared due to changes in the binding matrix and not crystal dissolution, as SEM analyses showed crystal surfaces were not pitted or dissolved in low pH conditions. Biofouling communities face dramatic future changes with reductions in groups with hard exposed exoskeletons and domination by soft-bodied ascidians and sponges.