Effects of ocean warming and acidification on survival,growth and skeletal development in the early benthic juvenile sea urchin (Heliocidaris erythrogramma)

Co‐occurring ocean warming, acidification and reduced carbonate mineral saturation have significant impacts on marine biota, especially calcifying organisms. The effects of these stressors on development and calcification in newly metamorphosed juveniles (ca. 0.5 mm test diameter) of the intertidal sea urchin Heliocidaris erythrogramma, an ecologically important species in temperate Australia, were investigated in context with present and projected future conditions. Habitat temperature and pH/pCO₂ were documented to place experiments in a biologically and ecologically relevant context. These parameters fluctuated diurnally up to 10 °C and 0.45 pH units. The juveniles were exposed to three temperature (21, 23 and 25 °C) and four pH (8.1, 7.8, 7.6 and 7.4) treatments in all combinations, representing ambient sea surface conditions (21 °C, pH 8.1; pCO₂ 397; Ω_Ca 4.7; Ω_Ar 3.1), near‐future projected change (+2–4 °C, ?0.3–0.5 pH units; pCO₂ 400–1820; Ω_Ca 5.0–1.6; Ω_Ar 3.3–1.1), and extreme conditions experienced at low tide (+4 °C, ?0.3–0.7 pH units; pCO₂ 2850–2967; Ω_Ca 1.1–1.0; Ω_Ar 0.7–0.6). The lowest pH treatment (pH 7.4) was used to assess tolerance levels. Juvenile survival and test growth were resilient to current and near‐future warming and acidification. Spine development, however, was negatively affected by near‐future increased temperature (+2–4 °C) and extreme acidification (pH 7.4), with a complex interaction between stressors. Near‐future warming was the more significant stressor. Spine tips were dissolved in the pH 7.4 treatments. Adaptation to fluctuating temperature‐pH conditions in the intertidal may convey resilience to juvenile H. erythrogramma to changing ocean conditions, however, ocean warming and acidification may shift baseline intertidal temperature and pH/pCO₂ to levels that exceed tolerance limits.     

Noncalcifying larvae in a changing ocean: warming,not acidification/hypercapnia,is the dominant stressor on development of the sea star Meridiastra calcar

Climate change driven ocean warming and acidification is potentially detrimental to the sensitive planktonic life stages of benthic marine invertebrates. Research has focused on the effects of acidification on calcifying larvae with a paucity of data on species with alternate developmental strategies and on the interactive effects of warming and acidification. To determine the impact of climate change on a conspicuous component of the intertidal fauna of southeast Australia, the development of the noncalcifying lecithotrophic larvae of the sea star Meridiastra calcar was investigated in the setting of predicted ocean warming (+2 to 4 ^°C) and acidification (?0.4 to 0.6 pH units) for 2100 and beyond in all combinations of stressors. Temperature and pH were monitored in the habitat of M. calcar to place experiments in context with current environmental conditions. There was no effect of temperature or pH on cleavage stage embryos but later development (gastrula‐larvae) was negatively effected by a +2 to 4 ^°C warming and there was a negative effect of ?0.6 pH units on embryos reaching the hatched gastrula stage. Mortality and abnormal development in larvae increased significantly even with +2 ^°C warming and larval growth was impaired at +4 ^°C. For the range of temperature and pH conditions tested, there were no interactive effects of stressors across all stages monitored. For M. calcar, warming not acidification was the dominant stressor. A regression model incorporating data from this study and projected increasing SST for the region suggests an increase in larval mortality to 70% for M. calcar by 2100 in the absence of acclimation and adaptation. The broad distribution of this species in eastern Australia encompassing subtropical to cold temperate thermal regimes provides the possibility that local M. calcar populations may be sustained in a warming world through poleward migration of thermotolerant propagules, facilitated by the strong southward flow of the East Australian Current.     

Climate change and ocean acidification effects on seagrasses and marine macroalgae

Although seagrasses and marine macroalgae (macro‐autotrophs) play critical ecological roles in reef, lagoon, coastal and open‐water ecosystems, their response to ocean acidification (OA) and climate change is not well understood. In this review, we examine marine macro‐autotroph biochemistry and physiology relevant to their response to elevated dissolved inorganic carbon [DIC], carbon dioxide [CO₂], and lower carbonate [CO₃^2?] and pH. We also explore the effects of increasing temperature under climate change and the interactions of elevated temperature and [CO₂]. Finally, recommendations are made for future research based on this synthesis. A literature review of >100 species revealed that marine macro‐autotroph photosynthesis is overwhelmingly C₃ (≥ 85%) with most species capable of utilizing HCO₃^?; however, most are not saturated at current ocean [DIC]. These results, and the presence of CO₂‐only users, lead us to conclude that photosynthetic and growth rates of marine macro‐autotrophs are likely to increase under elevated [CO₂] similar to terrestrial C₃ species. In the tropics, many species live close to their thermal limits and will have to up‐regulate stress‐response systems to tolerate sublethal temperature exposures with climate change, whereas elevated [CO₂] effects on thermal acclimation are unknown. Fundamental linkages between elevated [CO₂] and temperature on photorespiration, enzyme systems, carbohydrate production, and calcification dictate the need to consider these two parameters simultaneously. Relevant to calcifiers, elevated [CO₂] lowers net calcification and this effect is amplified by high temperature. Although the mechanisms are not clear, OA likely disrupts diffusion and transport systems of H⁺ and DIC. These fluxes control micro‐environments that promote calcification over dissolution and may be more important than CaCO₃ mineralogy in predicting macroalgal responses to OA. Calcareous macroalgae are highly vulnerable to OA, and it is likely that fleshy macroalgae will dominate in a higher CO₂ ocean; therefore, it is critical to elucidate the research gaps identified in this review.     

Pacific-wide contrast highlights resistance of reef calcifiers to ocean acidification

Ocean acidification (OA) and its associated decline in calcium carbonate saturation states is one of the major threats that tropical coral reefs face this century. Previous studies of the effect of OA on coral reef calcifiers have described a wide variety of outcomes for studies using comparable partial pressure of CO₂ (pCO₂) ranges, suggesting that key questions remain unresolved. One unresolved hypothesis posits that heterogeneity in the response of reef calcifiers to high pCO₂ is a result of regional-scale variation in the responses to OA. To test this hypothesis, we incubated two coral taxa (Pocillopora damicornis and massive Porites) and two calcified algae (Porolithon onkodes and Halimeda macroloba) under 400, 700 and 1000 μatm pCO₂ levels in experiments in Moorea (French Polynesia), Hawaii (USA) and Okinawa (Japan), where environmental conditions differ. Both corals and H. macroloba were insensitive to OA at all three locations, while the effects of OA on P. onkodes were location-specific. In Moorea and Hawaii, calcification of P. onkodes was depressed by high pCO₂, but for specimens in Okinawa, there was no effect of OA. Using a study of large geographical scale, we show that resistance to OA of some reef species is a constitutive character expressed across the Pacific.     

Temperature,but not pH,compromises sea urchin fertilization and early development under near-future climate change scenarios

Global warming is causing ocean warming and acidification. The distribution of Heliocidaris erythrogramma coincides with the eastern Australia climate change hot spot, where disproportionate warming makes marine biota particularly vulnerable to climate change. In keeping with near-future climate change scenarios, we determined the interactive effects of warming and acidification on fertilization and development of this echinoid. Experimental treatments (20–26°C, pH 7.6–8.2) were tested in all combinations for the ‘business-as-usual’ scenario, with 20°C/pH 8.2 being ambient. Percentage of fertilization was high (>89%) across all treatments. There was no difference in percentage of normal development in any pH treatment. In elevated temperature conditions, +4°C reduced cleavage by 40 per cent and +6°C by a further 20 per cent. Normal gastrulation fell below 4 per cent at +6°C. At 26°C, development was impaired. As the first study of interactive effects of temperature and pH on sea urchin development, we confirm the thermotolerance and pH resilience of fertilization and embryogenesis within predicted climate change scenarios, with negative effects at upper limits of ocean warming. Our findings place single stressor studies in context and emphasize the need for experiments that address ocean warming and acidification concurrently. Although ocean acidification research has focused on impaired calcification, embryos may not reach the skeletogenic stage in a warm ocean.     

Ocean warming and acidification alter the behavioral response to flow of the sea urchin Paracentrotus lividus

Ocean warming (OW) and acidification (OA) are intensively investigated as they pose major threats to marine organism. However, little effort is dedicated to another collateral climate change stressor, the increased frequency, and intensity of storm events, here referred to as intensified hydrodynamics. A 2‐month experiment was performed to identify how OW and OA (temperature: 21°C; pH_T: 7.7, 7.4; control: 17°C‐pH_T7.9) affect the resistance to hydrodynamics in the sea urchin Paracentrotus lividus using an integrative approach that includes physiology, biomechanics, and behavior. Biomechanics was studied under both no‐flow condition at the tube foot (TF) scale and flow condition at the individual scale. For the former, TF disk adhesive properties (attachment strength, tenacity) and TF stem mechanical properties (breaking force, extensibility, tensile strength, stiffness, toughness) were evaluated. For the latter, resistance to flow was addressed as the flow velocity at which individuals detached. Under near‐ and far‐future OW and OA, individuals fully balanced their acid‐base status, but skeletal growth was halved. TF adhesive properties were not affected by treatments. Compared to the control, mechanical properties were in general improved under pH_T7.7 while in the extreme treatment (21°C‐pH_T7.4) breaking force was diminished. Three behavioral strategies were implemented by sea urchins and acted together to cope with flow: improving TF attachment, streamlining, and escaping. Behavioral responses varied according to treatment and flow velocity. For instance, individuals at 21°C‐pH_T7.4 increased the density of attached TF at slow flows or controlled TF detachment at fast flows to compensate for weakened TF mechanical properties. They also showed an absence of streamlining favoring an escaping behavior as they ventured in a riskier faster movement at slow flows. At faster flows, the effects of OW and OA were detrimental causing earlier dislodgment. These plastic behaviors reflect a potential scope for acclimation in the field, where this species already experiences diel temperature and pH fluctuations.     

The stunting effect of a high CO2 ocean on calcification and development in sea urchin larvae,a synthesis from the tropics to the poles

The stunting effect of ocean acidification on development of calcifying invertebrate larvae has emerged as a significant effect of global change. We assessed the arm growth response of sea urchin echinoplutei, here used as a proxy of larval calcification, to increased seawater acidity/pCO₂ and decreased carbonate mineral saturation in a global synthesis of data from 15 species. Phylogenetic relatedness did not influence the observed patterns. Regardless of habitat or latitude, ocean acidification impedes larval growth with a negative relationship between arm length and increased acidity/pCO₂ and decreased carbonate mineral saturation. In multiple linear regression models incorporating these highly correlated parameters, pCO₂ exerted the greatest influence on decreased arm growth in the global dataset and also in the data subsets for polar and subtidal species. Thus, reduced growth appears largely driven by organism hypercapnia. For tropical species, decreased carbonate mineral saturation was most important. No single parameter played a dominant role in arm size reduction in the temperate species. For intertidal species, the models were equivocal. Levels of acidification causing a significant (approx. 10–20+%) reduction in arm growth varied between species. In 13 species, reduction in length of arms and supporting skeletal rods was evident in larvae reared in near-future (pCO₂ 800+ µatm) conditions, whereas greater acidification (pCO₂ 1000+ µatm) reduced growth in all species. Although multi-stressor studies are few, when temperature is added to the stressor mix, near-future warming can reduce the negative effect of acidification on larval growth. Broadly speaking, responses of larvae from across world regions showed similar trends despite disparate phylogeny, environments and ecology. Larval success may be the bottleneck for species success with flow-on effects for sea urchin populations and marine ecosystems.     

Meta‐analysis reveals enhanced growth of marine harmful algae from temperate regions with warming and elevated CO2 levels

Elevated pCO₂ and warming may promote algal growth and toxin production, and thereby possibly support the proliferation and toxicity of harmful algal blooms (HABs). Here, we tested whether empirical data support this hypothesis using a meta‐analytic approach and investigated the responses of growth rate and toxin content or toxicity of numerous marine and estuarine HAB species to elevated pCO₂ and warming. Most of the available data on HAB responses towards the two tested climate change variables concern dinoflagellates, as many members of this phytoplankton group are known to cause HAB outbreaks. Toxin content and toxicity did not reveal a consistent response towards both tested climate change variables, while growth rate increased consistently with elevated pCO₂. Warming also led to higher growth rates, but only for species isolated at higher latitudes. The observed gradient in temperature growth responses shows the potential for enhanced development of HABs at higher latitudes. Increases in growth rates with more CO₂ may present an additional competitive advantage for HAB species, particularly as CO₂ was not shown to enhance growth rate of other non‐HAB phytoplankton species. However, this may also be related to the difference in representation of dinoflagellate and diatom species in the respective HAB and non‐HAB phytoplankton groups. Since the proliferation of HAB species may strongly depend on their growth rates, our results warn for a greater potential of dinoflagellate HAB development in future coastal waters, particularly in temperate regions.     

Linking genotype to phenotype in a changing ocean: inferring the genomic architecture of a blue mussel stress response with genome‐wide association

A key component to understanding the evolutionary response to a changing climate is linking underlying genetic variation to phenotypic variation in stress response. Here, we use a genome‐wide association approach (GWAS) to understand the genetic architecture of calcification rates under simulated climate stress. We take advantage of the genomic gradient across the blue mussel hybrid zone (Mytilus edulis and Mytilus trossulus) in the Gulf of Maine (GOM) to link genetic variation with variance in calcification rates in response to simulated climate change. Falling calcium carbonate saturation states are predicted to negatively impact many marine organisms that build calcium carbonate shells – like blue mussels. We sampled wild mussels and measured net calcification phenotypes after exposing mussels to a ‘climate change’ common garden, where we raised temperature by 3°C, decreased pH by 0.2 units and limited food supply by filtering out planktonic particles >5 μm, compared to ambient GOM conditions in the summer. This climate change exposure greatly increased phenotypic variation in net calcification rates compared to ambient conditions. We then used regression models to link the phenotypic variation with over 170 000 single nucleotide polymorphism loci (SNPs) generated by genotype by sequencing to identify genomic locations associated with calcification phenotype, and estimate heritability and architecture of the trait. We identified at least one of potentially 2–10 genomic regions responsible for 30% of the phenotypic variation in calcification rates that are potential targets of natural selection by climate change. Our simulations suggest a power of 13.7% with our study's average effective sample size of 118 individuals and rare alleles, but a power of >90% when effective sample size is 900.     

Mechanical robustness of the calcareous tubeworm Hydroides elegans: warming mitigates the adverse effects of ocean acidification

Development of antifouling strategies requires knowledge of how fouling organisms would respond to climate change associated environmental stressors. Here, a calcareous tube built by the tubeworm, Hydroides elegans, was used as an example to evaluate the individual and interactive effects of ocean acidification (OA), warming and reduced salinity on the mechanical properties of a tube. Tubeworms produce a mechanically weaker tube with less resistance to simulated predator attack under OA (pH 7.8). Warming (29°C) increased tube volume, tube mineral density and the tube’s resistance to a simulated predatory attack. A weakening effect by OA did not make the removal of tubeworms easier except for the earliest stage, in which warming had the least effect. Reduced salinity (27 psu) did not affect tubes. This study showed that both mechanical analysis and computational modeling can be integrated with biofouling research to provide insights into how fouling communities might develop in future ocean conditions.     

Detrimental effects of ocean acidification on the economically important Mediterranean red coral (Corallium rubrum)

The mean predicted decrease of 0.3–0.4 pH units in the global surface ocean by the end of the century has prompted urgent research to assess the potential effects of ocean acidification on the marine environment, with strong emphasis on calcifying organisms. Among them, the Mediterranean red coral (Corallium rubrum) is expected to be particularly susceptible to acidification effects, due to the elevated solubility of its Mg‐calcite skeleton. This, together with the large overexploitation of this species, depicts a bleak future for this organism over the next decades. In this study, we evaluated the effects of low pH on the species from aquaria experiments. Several colonies of C. rubrum were long‐term maintained for 314 days in aquaria at two different pH levels (8.10 and 7.81, pH_T). Calcification rate, spicule morphology, major biochemical constituents (protein, carbohydrates and lipids) and fatty acids composition were measured periodically. Exposure to lower pH conditions caused a significant decrease in the skeletal growth rate in comparison with the control treatment. Similarly, the spicule morphology clearly differed between both treatments at the end of the experiment, with aberrant shapes being observed only under the acidified conditions. On the other hand, while total organic matter was significantly higher under low pH conditions, no significant differences were detected between treatments regarding total carbohydrate, lipid, protein and fatty acid composition. However, the lower variability found among samples maintained in acidified conditions relative to controls, suggests a possible effect of pH decrease on the metabolism of the colonies. Our results show, for the first time, evidence of detrimental ocean acidification effects on this valuable and endangered coral species.     

Nitrogen source and pCO2 synergistically affect carbon allocation,growth and morphology of the coccolithophore Emiliania huxleyi: potential implications of ocean acidification for the carbon cycle

Coccolithophores are unicellular phytoplankton that produce calcium carbonate coccoliths as an exoskeleton. Emiliania huxleyi, the most abundant coccolithophore in the world's ocean, plays a major role in the global carbon cycle by regulating the exchange of CO₂ across the ocean‐atmosphere interface through photosynthesis and calcium carbonate precipitation. As CO₂ concentration is rising in the atmosphere, the ocean is acidifying and ammonium (NH₄⁺) concentration of future ocean water is expected to rise. The latter is attributed to increasing anthropogenic nitrogen (N) deposition, increasing rates of cyanobacterial N₂ fixation due to warmer and more stratified oceans, and decreased rates of nitrification due to ocean acidification. Thus, future global climate change will cause oceanic phytoplankton to experience changes in multiple environmental parameters including CO₂, pH, temperature and nitrogen source. This study reports on the combined effect of elevated pCO₂ and increased NH₄⁺ to nitrate (NO₃^?) ratio (NH₄⁺/NO₃^?) on E. huxleyi, maintained in continuous cultures for more than 200 generations under two pCO₂ levels and two different N sources. Herein, we show that NH₄⁺ assimilation under N‐replete conditions depresses calcification at both low and high pCO₂, alters coccolith morphology, and increases primary production. We observed that N source and pCO₂ synergistically drive growth rates, cell size, and the ratio of inorganic to organic carbon. These responses to N source suggest that, compared to increasing CO₂ alone, a greater disruption of the organic carbon pump could be expected in response to the combined effect of increased NH₄⁺/NO₃^? ratio and CO₂ level in the future acidified ocean. Additional experiments conducted under lower nutrient conditions are needed prior to extrapolating our findings to the global oceans. Nonetheless, our results emphasize the need to assess combined effects of multiple environmental parameters on phytoplankton biology to develop accurate predictions of phytoplankton responses to ocean acidification.     

Temperature and CO2 additively regulate physiology,morphology and genomic responses of larval sea urchins,Strongylocentrotus purpuratus

Ocean warming and ocean acidification, both consequences of anthropogenic production of CO₂, will combine to influence the physiological performance of many species in the marine environment. In this study, we used an integrative approach to forecast the impact of future ocean conditions on larval purple sea urchins (Strongylocentrotus purpuratus) from the northeast Pacific Ocean. In laboratory experiments that simulated ocean warming and ocean acidification, we examined larval development, skeletal growth, metabolism and patterns of gene expression using an orthogonal comparison of two temperature (13°C and 18°C) and pCO₂ (400 and 1100 μatm) conditions. Simultaneous exposure to increased temperature and pCO₂ significantly reduced larval metabolism and triggered a widespread downregulation of histone encoding genes. pCO₂ but not temperature impaired skeletal growth and reduced the expression of a major spicule matrix protein, suggesting that skeletal growth will not be further inhibited by ocean warming. Importantly, shifts in skeletal growth were not associated with developmental delay. Collectively, our results indicate that global change variables will have additive effects that exceed thresholds for optimized physiological performance in this keystone marine species.     

Circumpolar dynamics of a marine top‐predator track ocean warming rates

Global warming is a nonlinear process, and temperature may increase in a stepwise manner. Periods of abrupt warming can trigger persistent changes in the state of ecosystems, also called regime shifts. The responses of organisms to abrupt warming and associated regime shifts can be unlike responses to periods of slow or moderate change. Understanding of nonlinearity in the biological responses to climate warming is needed to assess the consequences of ongoing climate change. Here, we demonstrate that the population dynamics of a long‐lived, wide‐ranging marine predator are associated with changes in the rate of ocean warming. Data from 556 colonies of black‐legged kittiwakes Rissa tridactyla distributed throughout its breeding range revealed that an abrupt warming of sea‐surface temperature in the 1990s coincided with steep kittiwake population decline. Periods of moderate warming in sea temperatures did not seem to affect kittiwake dynamics. The rapid warming observed in the 1990s may have driven large‐scale, circumpolar marine ecosystem shifts that strongly affected kittiwakes through bottom‐up effects. Our study sheds light on the nonlinear response of a circumpolar seabird to large‐scale changes in oceanographic conditions and indicates that marine top predators may be more sensitive to the rate of ocean warming rather than to warming itself.     

Slow‐flow habitats as refugia for coastal calcifiers from ocean acidification

The pH of the oceans’ surface water is dropping, termed ocean acidification (OA), and the 0.4 unit reduction in pH by 2100 is projected to negatively impact benthic coastal organisms that produce calcium carbonate “skeletons.” Research has focussed on identifying species that are susceptible to OA, but there is an urgent need to discover refuge habitats that will afford protection to vulnerable species. The susceptibility of calcium carbonate skeletons to dissolution by OA depends on the pH at their surface, and this is controlled by the interaction between seawater velocity and organismal metabolism. This perspective considers how seawater velocity modifies the responses of calcifying organisms (seaweed, shellfish, and tropical corals) to OA through its action on controlling diffusion boundary layer thickness and thereby the pH and calcium carbonate saturation state (Ω) at the organisms’ surface. Evidence is presented to support the idea that slow‐flow habitats, such as wave‐sheltered bays or the within canopies of seaweed/seagrass beds, might provide inexpensive refugia from OA for vulnerable coastal calcifiers.     

Meta‐analysis reveals complex marine biological responses to the interactive effects of ocean acidification and warming

Ocean acidification and warming are considered two of the greatest threats to marine biodiversity, yet the combined effect of these stressors on marine organisms remains largely unclear. Using a meta‐analytical approach, we assessed the biological responses of marine organisms to the effects of ocean acidification and warming in isolation and combination. As expected biological responses varied across taxonomic groups, life‐history stages, and trophic levels, but importantly, combining stressors generally exhibited a stronger biological (either positive or negative) effect. Using a subset of orthogonal studies, we show that four of five of the biological responses measured (calcification, photosynthesis, reproduction, and survival, but not growth) interacted synergistically when warming and acidification were combined. The observed synergisms between interacting stressors suggest that care must be made in making inferences from single‐stressor studies. Our findings clearly have implications for the development of adaptive management strategies particularly given that the frequency of stressors interacting in marine systems will be likely to intensify in the future. There is now an urgent need to move toward more robust, holistic, and ecologically realistic climate change experiments that incorporate interactions. Without them accurate predictions about the likely deleterious impacts to marine biodiversity and ecosystem functioning over the next century will not be possible.     

Adaptation and acclimatization to ocean acidification in marine ectotherms: an in situ transplant experiment with polychaetes at a shallow CO2 vent system

Metabolic rate determines the physiological and life-history performances of ectotherms. Thus, the extent to which such rates are sensitive and plastic to environmental perturbation is central to an organism''s ability to function in a changing environment. Little is known of long-term metabolic plasticity and potential for metabolic adaptation in marine ectotherms exposed to elevated pCO₂. Consequently, we carried out a series of in situ transplant experiments using a number of tolerant and sensitive polychaete species living around a natural CO₂ vent system. Here, we show that a marine metazoan (i.e. Platynereis dumerilii) was able to adapt to chronic and elevated levels of pCO₂. The vent population of P. dumerilii was physiologically and genetically different from nearby populations that experience low pCO₂, as well as smaller in body size. By contrast, different populations of Amphiglena mediterranea showed marked physiological plasticity indicating that adaptation or acclimatization are both viable strategies for the successful colonization of elevated pCO₂ environments. In addition, sensitive species showed either a reduced or increased metabolism when exposed acutely to elevated pCO₂. Our findings may help explain, from a metabolic perspective, the occurrence of past mass extinction, as well as shed light on alternative pathways of resilience in species facing ongoing ocean acidification.     

Going with the flow: the role of ocean circulation in global marine ecosystems under a changing climate

Ocean warming, acidification, deoxygenation and reduced productivity are widely considered to be the major stressors to ocean ecosystems induced by emissions of CO₂. However, an overlooked stressor is the change in ocean circulation in response to climate change. Strong changes in the intensity and position of the western boundary currents have already been observed, and the consequences of such changes for ecosystems are beginning to emerge. In this study, we address climatically induced changes in ocean circulation on a global scale but relevant to propagule dispersal for species inhabiting global shelf ecosystems, using a high‐resolution global ocean model run under the IPCC RCP 8.5 scenario. The ¼ degree model resolution allows improved regional realism of the ocean circulation beyond that of available CMIP5‐class models. We use a Lagrangian approach forced by modelled ocean circulation to simulate the circulation pathways that disperse planktonic life stages. Based on trajectory backtracking, we identify present‐day coastal retention, dominant flow and dispersal range for coastal regions at the global scale. Projecting into the future, we identify areas of the strongest projected circulation change and present regional examples with the most significant modifications in their dominant pathways. Climatically induced changes in ocean circulation should be considered as an additional stressor of marine ecosystems in a similar way to ocean warming or acidification.     

Silent oceans: ocean acidification impoverishes natural soundscapes by altering sound production of the world's noisiest marine invertebrate

Soundscapes are multidimensional spaces that carry meaningful information for many species about the location and quality of nearby and distant resources. Because soundscapes are the sum of the acoustic signals produced by individual organisms and their interactions, they can be used as a proxy for the condition of whole ecosystems and their occupants. Ocean acidification resulting from anthropogenic CO₂ emissions is known to have profound effects on marine life. However, despite the increasingly recognized ecological importance of soundscapes, there is no empirical test of whether ocean acidification can affect biological sound production. Using field recordings obtained from three geographically separated natural CO₂ vents, we show that forecasted end-of-century ocean acidification conditions can profoundly reduce the biological sound level and frequency of snapping shrimp snaps. Snapping shrimp were among the noisiest marine organisms and the suppression of their sound production at vents was responsible for the vast majority of the soundscape alteration observed. To assess mechanisms that could account for these observations, we tested whether long-term exposure (two to three months) to elevated CO₂ induced a similar reduction in the snapping behaviour (loudness and frequency) of snapping shrimp. The results indicated that the soniferous behaviour of these animals was substantially reduced in both frequency (snaps per minute) and sound level of snaps produced. As coastal marine soundscapes are dominated by biological sounds produced by snapping shrimp, the observed suppression of this component of soundscapes could have important and possibly pervasive ecological consequences for organisms that use soundscapes as a source of information. This trend towards silence could be of particular importance for those species whose larval stages use sound for orientation towards settlement habitats.