Adult acclimation to combined temperature and pH stressors significantly enhances reproductive outcomes compared to short-term exposures

Ocean warming and acidification adjust inter- and intra-specific variability in the functional trait expression of polar invertebrates

Climate change is known to affect the distribution and composition of species, but concomitant alterations to functionally important aspects of behaviour and species-environment relations are poorly constrained. Here, we examine the ecosystem ramifications of changes in sediment-dwelling invertebrate bioturbation behaviour-a key process mediating nutrient cycling-associated with near-future environmental conditions (+ 1.5 °C, 550 ppm [pCO2]) for species from polar regions experiencing rapid rates of climate change. We find that responses to warming and acidification vary between species and lead to a reduction in intra-specific variability in behavioural trait expression that adjusts the magnitude and direction of nutrient concentrations. Our analyses also indicate that species behaviour is not predetermined, but can be dependent on local variations in environmental history that set population capacities for phenotypic plasticity. We provide evidence that certain, but subtle, aspects of inter- and intra-specific variation in behavioural trait expression, rather than the presence or proportional representation of species per se, is an important and under-appreciated determinant of benthic biogeochemical responses to climate change. Such changes in species behaviour may act as an early warning for impending ecological transitions associated with progressive climate forcing.

Transgenerational acclimation to acidified seawater and gene expression patterns in a sea urchin

Transgenerational responses of susceptible calcifying organisms to progressive ocean acidification are an important issue in reducing uncertainty of future predictions. In this study, a two-generation rearing experiment was conducted using mature Mesocentrotus nudus, a major edible sea urchin that occurs along the coasts of northern Japan. Morphological observations and comprehensive gene expression analysis (RNA-seq) of resulting larvae were performed to examine transgenerational acclimation to acidified seawater. Two generations of rearing experiments showed that larvae derived from parents acclimated to acidified seawater tended to have higher survival and show less reduction in body size when exposed to acidified seawater of the same pH, suggesting that a positive carry-over effect occurred. RNA-seq analysis showed that gene expression patterns of larvae originated from both acclimated and non-acclimated parents to acidified seawater tended to be different than control condition, and the gene expression pattern of larvae originated from acclimated parents was substantially different than that of larvae of non-acclimated and control parents.

Behavioural and physiological impacts of low salinity on the sea urchin Echinus esculentus

Reduced seawater salinity as a result of freshwater input can exert a major influence on the ecophysiology of benthic marine invertebrates, such as echinoderms. While numerous experimental studies have explored the physiological and behavioural effects of short-term, acute exposure to low salinity in echinoids, surprisingly few have investigated the consequences of chronic exposure, or compared the two. In this study, the European sea urchin, Echinus esculentus, was exposed to low salinity over the short term (11‰, 16‰, 21‰, 26‰ and 31‰ for 24 h) and longer term (21, 26 and 31‰ for 25 days). Over the short term, oxygen consumption, activity coefficient and coelomic fluid osmolality were directly correlated with reduced salinity, with 100% survival at ≥21‰ and 0% at ≤16‰. Over the longer term at 21‰ (25 days), oxygen consumption was significantly higher, feeding was significantly reduced and activity coefficient values were significantly lower than at control salinity (31‰). At 26‰, all metrics were comparable to the control by the end of the experiment, suggesting acclimation. Furthermore, beneficial functional resistance (righting ability and metabolic capacity) to acute low salinity was observed at 26‰. Osmolality values were slightly hyperosmotic to the external seawater at all acclimation salinities, while coelomocyte composition and concentration were unaffected by chronic low salinity. Overall, E. esculentus demonstrate phenotypic plasticity that enables acclimation to reduced salinity around 26‰; however, 21‰ represents a lower acclimation threshold, potentially limiting its distribution in coastal areas prone to high freshwater input.

Severe 21st-century ocean acidification in Antarctic Marine Protected Areas

Antarctic coastal waters are home to several established or proposed Marine Protected Areas (MPAs) supporting exceptional biodiversity. Despite being threatened by anthropogenic climate change, uncertainties remain surrounding the future ocean acidification (OA) of these waters. Here we present 21st-century projections of OA in Antarctic MPAs under four emission scenarios using a high-resolution ocean-sea ice-biogeochemistry model with realistic ice-shelf geometry. By 2100, we project pH declines of up to 0.36 (total scale) for the top 200 m. Vigorous vertical mixing of anthropogenic carbon produces severe OA throughout the water column in coastal waters of proposed and existing MPAs. Consequently, end-of-century aragonite undersaturation is ubiquitous under the three highest emission scenarios. Given the cumulative threat to marine ecosystems by environmental change and activities such as fishing, our findings call for strong emission-mitigation efforts and further management strategies to reduce pressures on ecosystems, such as the continuation and expansion of Antarctic MPAs.

Resilience against the impacts of climate change in an ecologically and economically significant native oyster

Climate change is acidifying and warming our oceans, at an unprecedented rate posing a challenge for marine invertebrates vital across the globe for ecological services and food security. Here we show it is possible for resilience to climate change in an ecologically and economically significant oyster without detrimental effects to the energy budget. We exposed 24 pair-mated genetically distinct families of the Sydney rock oyster, Saccostrea glomerata to ocean acidification and warming for 4w and measured their resilience. Resilience was identified as the capacity to defend their acid-base balance without a loss of energy available for Scope for Growth (SFG). Of the 24 families, 13 were better able to defend their acid-base balance while eight had no loss of energy availability with a positive SFG. This study has found oyster families with reslience against climate change without a loss of SFG, is an essential mitigation strategy, in a critical mollusc.

Acclimation of the Antarctic sea urchin Sterechinus neumayeri to warmer temperatures involves a modulation of cellular machinery

Global warming is threatening marine Antarctic fauna, which has evolved in isolation in a cold environment for millions of years. Facing increasing temperatures, marine Antarctic invertebrates can either tolerate or develop adaptations to these changes. On a short timescale, their survival and resistance to warming will be driven by the efficiency of their phenotypic plasticity through their capacity for acclimation. The current study aims at evaluating the capacity for acclimation of the Antarctic sea urchin Sterechinus neumayeri to predicted ocean warming scenarios (+2, RCP 2.6 and + 4 °C, RCP 8.5, IPCC et al., 2019) and deciphering the subcellular mechanisms underlying their acclimation. A combination of transcriptomics, physiological (e.g. growth rate, gonad growth, ingestion rate and oxygen consumption), and behavioral-based approaches were used on individuals incubated at 1, 3 and, 5 °C for 22 weeks. Mortality was low at warmer temperatures (20%) and oxygen consumption and ingestion rate seemed to reach a stable state around 16 weeks suggesting that S. neumayeri might be able to acclimate to warmer temperatures (until 5 °C). Transcriptomic analyses highlighted adjustments of the cellular machinery with the activation of replication, recombination, and repair processes as well as cell cycle and division and repression of transcriptional and signal transduction mechanisms and defense processes. These results suggest that acclimation to warmer scenarios might require more than 22 weeks for the Antarctic Sea urchins S. neumayeri but that projections of climate change for the end of the century may not strongly affect the population of S. neumayeri of this part of the Antarctic.

Embryonic encapsulated development of the gastropod Acanthina monodon is impacted by future environmental changes of temperature and pCO2

Egg capsules of the gastropod Acanthina monodon were maintained during the entire period of encapsulated development at three temperatures (10, 15, 20 °C) and two pCO₂ levels (400, 1200 μatm). Embryos per capsule, size at hatching, time to hatching, embryonic metabolic rates, and the resistance of juveniles to shell breakage were quantified. No embryos maintained at 20 °C developed to hatching. The combination of temperature and pCO₂ levels had synergistic effects on hatching time and developmental success, antagonistic effects on number of hatchlings per capsule, resistance to juvenile shell cracking and metabolism, and additive effect on hatching size. Juveniles hatched significantly sooner at 15 °C, independent of the pCO₂ level that they had been exposed to, while individuals hatched at significantly smaller sizes if they had been held under 15 °C/1200 μatm rather than at 10 °C/low pCO₂. Embryos held at the higher pCO₂ had a significantly greater percentage of abnormalities. For capsules maintained at low pCO₂ and 15 °C, emerging juveniles had less resistance to shell breakage. Embryonic metabolism was significantly higher at 15 °C than at 10 °C, independent of pCO₂ level. The lower metabolism occurred in embryos maintained at the higher pCO₂ level. Thus, in this study, temperature was the factor that had the greatest effect on the encapsulated development of A. monodon, increasing the metabolism of the embryos and consequently accelerating development, which was expressed in a shorter intracapsular development time, but with smaller individuals at hatching and a lower resistance of their shells to breakage. On the other hand, the high pCO₂ level suppressed metabolism, prolonged intracapsular development, and promoted more incomplete development of the embryos. However, the combination of the two factors can mitigate--to some extent--the adverse effects of both incomplete development and lower resistance to shell breakage.

Parental exposure to ocean acidification impacts gamete production and physiology but not offspring performance in Nematostella vectensis

Ocean acidification (OA) resulting from anthropogenic CO2 emissions is impairing the reproduction of marine organisms. While parental exposure to OA can protect offspring via carryover effects, this phenomenon is poorly understood in many marine invertebrate taxa. Here, we examined how parental exposure to acidified (pH 7.40) versus ambient (pH 7.72) seawater influenced reproduction and offspring performance across six gametogenic cycles (13 weeks) in the estuarine sea anemone Nematostella vectensis. Females exhibited reproductive plasticity under acidic conditions, releasing significantly fewer but larger eggs compared to ambient females after 4 weeks of exposure, and larger eggs in two of the four following spawning cycles despite recovering fecundity, indicating long-term acclimatization and greater investment in eggs. Males showed no changes in fecundity under acidic conditions but produced a greater percentage of sperm with high mitochondrial membrane potential (MMP; a proxy for elevated motility), which corresponded with higher fertilization rates relative to ambient males. Finally, parental exposure to acidic conditions did not significantly influence offspring development rates, respiration rates, or heat tolerance. Overall, this study demonstrates that parental exposure to acidic conditions impacts gamete production and physiology but not offspring performance in N. vectensis, suggesting that increased investment in individual gametes may promote fitness.

The added costs of winter ocean warming for metabolism, arm regeneration and survival in the brittle star Ophionereis schayeri

As the climate continues to change, it is not just the magnitude of these changes that is important - equally critical is the timing of these events. Conditions that may be well tolerated at one time can become detrimental if experienced at another, as a result of seasonal acclimation. Temperature is the most critical variable as it affects most aspects of an organism's physiology. To address this, we quantified arm regeneration and respiration in the Australian brittle star Ophionereis schayeri for 10 weeks in response to a +3°C warming (18.5°C, simulating a winter heatwave) compared with ambient winter temperature (15.5°C). The metabolic scaling rate (b=0.635 at 15.5°C and 0.746 at 18.5°C) with respect to size was similar to that of other echinoderms and was not affected by temperature. Elevated temperature resulted in up to a 3-fold increase in respiration and a doubling of regeneration growth; however, mortality was greater (up to 44.2% at 18.5°C), especially in the regenerating brittle stars. Metabolic rate of the brittle stars held at 18.5°C was much higher than expected (Q10≈23) and similar to that of O. schayeri tested in summer, which was near their estimated thermotolerance limits. The additional costs associated with the elevated metabolism and regeneration rates incurred by the unseasonably warm winter temperatures may lead to increased mortality and predation risk.

Gene Expression Detects the Factors Influencing the Reproductive Success and the Survival Rates of Paracentrotus lividus Offspring

The increase in the demand for Paracentrotus lividus roe, a food delicacy, causes increased pressure on its wild stocks. In this scenario, aquaculture facilities will mitigate the effects of anthropogenic pressures on the wild stocks of P. lividus. Consequently, experimental studies should be conducted to enhance techniques to improve efficient aquaculture practices for these animals. Here, we for the first time performed molecular investigations on cultured sea urchins. We aimed at understanding if maternal influences may significantly impact the life of future offspring, and how the culture conditions may impact the development and growth of cultured specimens. Our findings demonstrate that the outcomes of in vitro fertilization of P. lividus are influenced by maternal influences, but these effects are largely determined by culture conditions. In fact, twenty-three genes involved in the response to stress and skeletogenesis, whose expressions were measured by Real Time qPCR, were differently expressed in sea urchins cultured in two experimental conditions, and the results were largely modified in offspring deriving from two groups of females. The findings herein reported will be critical to develop protocols for the larval culture of the most common sea urchin, both for research and industrial production purposes for mass production.

Live-fast-die-young: Carryover effects of heatwave-exposed adult urchins on the development of the next generation

With rising ocean temperatures, extreme weather events such as marine heatwaves (MHWs) are increasing in frequency and duration, pushing marine life beyond their physiological limits. The potential to respond to extreme conditions through physiological acclimatization, and pass on resistance to the next generation, fundamentally depends on the capacity of an organism to cope within their thermal tolerance limits. To elucidate whether heat conditioning of parents could benefit offspring development, we exposed adult sea urchins (Heliocidaris erythrogramma) to ambient summer (23°C), moderate (25°C) or strong (26°C) MHW conditions for 10 days. Offspring were then reared at constant temperature along a thermal gradient (22-28°C) and development was tracked to the 14-day juvenile stage. Progeny from the MHW-conditioned adults developed through to metamorphosis faster than those of ambient conditioned parents, with most individuals from the moderate and strong heatwaves developing to the larval stage across all temperatures. In contrast, the majority of offspring from the control summer temperature died before metamorphosis at temperatures above 25°C (moderate MHW). Juveniles produced from the strong MHW-conditioned adults were also larger across all temperatures, with the largest juveniles in the 26°C treatment. In contrast, the smallest juveniles were from control (current-day summer) parents (and reared at 22 and 25°C). Surprisingly, initial survival was higher in the progeny of MHW exposed parents, even at temperatures hotter than predicted MHWs (28°C). Importantly, however, there was substantial mortality of juveniles from the strong MHW parents by day 14. Therefore, while carryover effects of parental conditioning to MHWs resulted in faster growing, larger progeny, this benefit will only persist beyond the more sensitive juvenile stage and enhance survival if conditions return promptly to normal seasonal temperatures within current thermal tolerance limits.

Is Ocean Acidification Really a Threat to Marine Calcifiers? A Systematic Review and Meta-Analysis of 980+ Studies Spanning Two Decades

Ocean acidification is considered detrimental to marine calcifiers, but mounting contradictory evidence suggests a need to revisit this concept. This systematic review and meta-analysis aim to critically re-evaluate the prevailing paradigm of negative effects of ocean acidification on calcifiers. Based on 5153 observations from 985 studies, many calcifiers (e.g., echinoderms, crustaceans, and cephalopods) are found to be tolerant to near-future ocean acidification (pH ≈ 7.8 by the year 2100), but coccolithophores, calcifying algae, and corals appear to be sensitive. Calcifiers are generally more sensitive at the larval stage than adult stage. Over 70% of the observations in growth and calcification are non-negative, implying the acclimation capacity of many calcifiers to ocean acidification. This capacity can be mediated by phenotypic plasticity (e.g., physiological, mineralogical, structural, and molecular adjustments), transgenerational plasticity, increased food availability, or species interactions. The results suggest that the impacts of ocean acidification on calcifiers are less deleterious than initially thought as their adaptability has been underestimated. Therefore, in the forthcoming era of ocean acidification research, it is advocated that studying how marine organisms persist is as important as studying how they perish, and that future hypotheses and experimental designs are not constrained within the paradigm of negative effects.

Different ecological histories of sea urchins acclimated to reduced pH influence offspring response to multiple stressors

End-of-the-century predictions on carbon dioxide (CO₂) driven ocean acidification and the continuous leakage of pesticides from inland to coastal areas are of concern for potential negative effects on marine species' early life stages which are the most vulnerable to environmental changes. Variations in seawater chemistry related to human activities may interfere with the normal development from embryo to juvenile/adult stage. However, transgenerational studies suggest that the parental generation can influence the offspring phenotype, and thus their performances, based on the environment experienced. Here we compared the transgenerational responses to a multiple stressor scenario in sea urchins (Paracentrotus lividus) that experienced different environments since their settlement: i.e., animals from a highly variable environment, such as the Venice lagoon, versus animals from a coastal area with prevailing oligotrophic conditions in the Northern Adriatic Sea. After long-term maintenance (2 and 6 months) of adult sea urchins at natural and -0.4 units reduced pH, the F1 generations were obtained. Embryos were reared under four experimental conditions: natural and -0.4 pH both in the absence and in the presence of an emerging contaminants' mixture (glyphosate and aminomethylphosphonic acid at environmentally relevant concentrations, 100 μg/L). A significant detrimental effect of both the parental and the filial pH was highlighted, affecting embryo development and growth. Nonetheless, sea urchins from both sites were able to cope with ocean acidification. The 6-months F1 response was better than that of the 2-months F1. Conversely, the F1 response of the sea urchins maintained at natural conditions did not change sensibly after more prolonged parental exposure. An additive but mild negative effect of the mixture was observed, mostly in lagoon offspring. Results suggest that long-term exposure to reduced pH leads to transgenerational acclimation but does not affect susceptibility to the tested pollutants.

Acclimatory gene expression of primed clams enhances robustness to elevated pCO2

Sub-lethal exposure to environmental challenges may enhance ability to cope with chronic or repeated change, a process known as priming. In a previous study, pre-exposure to seawater enriched with pCO₂ improved growth and reduced antioxidant capacity of juvenile Pacific geoduck Panopea generosa, suggesting that transcriptional shifts may drive phenotypic modifications post-priming. To this end, juvenile clams were sampled and TagSeq gene expression data analyzed after 1) a 110-day acclimation under ambient (921 μatm, naïve) and moderately-elevated pCO₂ (2870 μatm, pre-exposed); then following 2) a second 7-day exposure to three pCO₂ treatments (ambient: 754 μatm; moderately-elevated: 2750 μatm; severely-elevated: 4940 μatm), a 7-day return to ambient pCO₂ , and a third 7-day exposure to two pCO₂ treatments (ambient: 967 μatm; moderately-elevated: 3030 μatm). Pre-exposed geoducks frontloaded genes for stress and apoptosis/innate immune response, homeostatic processes, protein degradation, and transcriptional modifiers. Pre-exposed geoducks were also responsive to subsequent encounters, with gene sets enriched for mitochondrial recycling and immune defense under elevated pCO₂ and energy metabolism and biosynthesis under ambient recovery. In contrast, gene sets with higher expression in naïve clams were enriched for fatty-acid degradation and glutathione components, suggesting naïve clams could be depleting endogenous fuels, with unsustainable energetic requirements if changes in carbonate chemistry persist. Collectively, our transcriptomic data indicates pCO₂ priming during post-larval periods could, via gene expression regulation, enhance robustness in bivalves to environmental change. Such priming approaches may be beneficial for aquaculture, as seafood demand intensifies concurrent with increasing climate change in marine systems.

Transgenerational effects and phenotypic plasticity in sperm and larvae of the sea urchin Paracentrotus lividus under ocean acidification

In marine organisms, differing degree of sensitivity to ocean acidification (OA) is expected for each life stage, and disturbance at one stage can carry over into the following stage or following generation. In this study we investigated phenotypic changes of sperm and larvae of the sea urchin Paracentrotus lividus in response to different pH conditions (8.0, 7.7, 7.4) experienced by the parents during gametogenesis. In sperm from two-months exposed males, sperm motility, velocity, ATP content, ATP consumption and respiration rate were evaluated at three pH values of the activating medium (8.0, 7.7 and 7.4). Moreover, larvae from each parental group were reared at pH 8.0 and 7.7 for 20 days and larval mortality and growth were then assessed. Sperm motility and respiration rate were not affected either by exposure of males to low pH or by the post-activation pH. Sperm velocity did not differ among post-activation pH values in all sperm groups, but it decreased slower in sperm developed under acidified conditions, suggesting the presence of positive carryover effect on sperm longevity. This positive carryover effect of exposure of males to low pH values was highlighted also for the sperm ATP content, which was higher in these groups of sperm. ATP consumption rate was affected by post-activation pH with higher values at pH 8.0 in sperm from males maintained at control condition and pH 7.7 while the energy consumption appeared to be differently modulated at different experimental conditions. A negative carry over effect of OA was observed on survival of larvae from parents acclimated at pH 7.4 and additive negative effects of both parental and larval exposure to low pH can be suggested. In all groups of larvae, decreased somatic growth was observed at low rearing pH, thus larvae from parents maintained at low pH did not show an increased capability to cope with OA.

Can heat shock protein 70 (HSP70) serve as biomarkers in Antarctica for future ocean acidification, warming and salinity stress?

The Antarctic Peninsula is one of the fastest-warming places on Earth. Elevated sea water temperatures cause glacier and sea ice melting. When icebergs melt into the ocean, it “freshens” the saltwater around them, reducing its salinity. The oceans absorb excess anthropogenic carbon dioxide (CO2) causing decline in ocean pH, a process known as ocean acidification. Many marine organisms are specifically affected by ocean warming, freshening and acidification. Due to the sensitivity of Antarctica to global warming, using biomarkers is the best way for scientists to predict more accurately future climate change and provide useful information or ecological risk assessments. The 70-kilodalton (kDa) heat shock protein (HSP70) chaperones have been used as biomarkers of stress in temperate and tropical environments. The induction of the HSP70 genes (Hsp70) that alter intracellular proteins in living organisms is a signal triggered by environmental temperature changes. Induction of Hsp70 has been observed both in eukaryotes and in prokaryotes as response to environmental stressors including increased and decreased temperature, salinity, pH and the combined effects of changes in temperature, acidification and salinity stress. Generally, HSP70s play critical roles in numerous complex processes of metabolism; their synthesis can usually be increased or decreased during stressful conditions. However, there is a question as to whether HSP70s may serve as excellent biomarkers in the Antarctic considering the long residence time of Antarctic organisms in a cold polar environment which appears to have greatly modified the response of heat responding transcriptional systems. This review provides insight into the vital roles of HSP70 that make them ideal candidates as biomarkers for identifying resistance and resilience in response to abiotic stressors associated with climate change, which are the effects of ocean warming, freshening and acidification in Antarctic organisms.

Large within, and between, species differences in marine cellular responses: Unpredictability in a changing environment

Predicting the impacts of altered environments on future biodiversity requires a detailed understanding of organism responses to change. To date, studies evaluating mechanisms underlying marine organism stress responses have largely concentrated on oxygen limitation and the use of heat shock proteins as biomarkers. However, whether these biomarkers represent responses that are consistent across species and different environmental stressors remains open to question. Here we show that responses to four different thermal stresses (three rates of thermal ramping (1 °C h^-1, 1 °C day^-1 or 1 °C 3 day^-1) and a three-month acclimation to warming of 2 °C) applied to three species of Antarctic marine invertebrate produced highly individual responses in gene expression profiles, both within and between species. Mapping the gene expression profiles from each treatment for each of the three species, identified considerable difference in numbers of differentially regulated transcripts ranging from 10 to 3011. When these data were correlated across the different temperature treatments, there was no evidence for a common response with only 0-2 transcripts shared between all four treatments within any one species. There were also no shared differentially expressed genes across species, even at the same thermal ramping rates. The classical cellular stress response (CSR) i.e. up-regulation of heat shock proteins, was only strongly present in two species at the fastest ramping rate of 1 °C h^-1, albeit with different sets of stress genes expressed in each species. These data demonstrate the wide variability in response to warming at the molecular level in marine species. Therefore, identification of biodiversity stress responses engendered by changing conditions will require evaluation at the species level using targeted key members of the ecosystem, strongly correlated to the local biotic and abiotic factors.

Negative carry-over effects on larval thermal tolerances across a natural thermal gradient

Under climate change, marine organisms will need to tolerate or adapt to increasing temperatures to persist. The ability of populations to cope with thermal stress may be influenced by conditions experienced by parents, by both genetic changes and transgenerational phenotypic plasticity through epigenetics or maternal provisioning. In organisms with complex life cycles, larval stages are particularly vulnerable to stress. Positive parental carry-over effects occur if more stressful parental environments yield more tolerant offspring while the opposite pattern leads to negative carry-over effects. This study evaluated the role of parental effects in determining larval thermal tolerances for the intertidal mussel, Mytilus californianus. We tested whether thermal environments across a natural gradient (shoreline elevation) impacted mussel temperature tolerances. Lethal thermal limits were compared for field-collected adults and their larvae. We observed parental effects across one generation, in which adult mussels exposed to warmer habitats yielded less tolerant offspring. Interestingly, although parental environments influenced offspring tolerances, we found no clear effects of habitat conditions on adult phenotypes (tolerances). We found indicators of trade-offs in energy investment, with higher reproductive condition and larger egg diameters in low stress environments. These results suggest that parental effects are negative, leading to possible adverse effects of thermal stress on the next generation.

Capacity of an ecologically key urchin to recover from extreme events: Physiological impacts of heatwaves and the road to recovery

Heatwaves are increasing in frequency and intensity, with substantial impacts on ecosystems and species which maintain their function. Whether or not species are harmed by heatwave conditions by being pushed beyond their physiological bounds can depend on whether energy replacement is sufficient to enable recovery from acute stress. We exposed an ecologically important sea urchin, Heliocidaris erythrogramma, to experimental marine heatwave scenarios in context with recent summer heat anomalies in moderate (25 °C), and strong heatwave (26 °C) conditions for 10 days, followed by a 10-day recovery period at normal summer temperature (23 °C). Greater heatwave intensity drove higher metabolic rates which were not matched with a concurrent increase in food consumption or faecal production. However, food consumption increased during the post-heatwave recovery period, likely to replenish an energy deficit. Despite this, mortality increased into the recovery period and seemed to be caused by latent effects, manifesting as a decline in health index as individuals progressed from spine and pedicellariae loss, through to loss of tube foot rigor, bald patch disease, culminating in mortality. We show for the first time that the acute thermal stress of heatwaves can have latent physiological effects that cause mortality even when conditions return to normal. Our results show that the negative effects of heatwaves can manifest after relief from stressful conditions and highlight the importance of understanding the latent effects on physiology and health. This understanding will offer insights into the long-term potential for stress recovery following seemingly sublethal effects and whether the restoration of ambient conditions post-heatwave is sufficient to ensure population stability.

Transgenerational responses to seawater pH in the edible oyster, with implications for the mariculture of the species under future ocean acidification

The majority of common edible oysters are projected to grow more slowly and have smaller impaired shells because of anthropogenic CO₂-induced reductions in seawater carbonate ion concentration and pH, a process called ocean acidification (OA). Recent evidence has shown that OA has carryover effects, for example, larvae exposed to OA will also exhibit either positive or negative effects after metamorphosis. This study examined the hidden carryover effects of OA exposure during parental and larval stages on post-metamorphic traits of the commercially important oyster species Crassostrea hongkongensis. Adults of C. hongkongensis were exposed to control pH (pH_NBS 8.0) and OA-induced low pH (pH_NBS 7.4) conditions. Their larval offspring were then exposed to the same aquarium conditions before being out-planted as post-metamorphic juveniles at a mariculture site for 10 months. Initially, larval offspring were resilient to low pH with or without parental exposure. The larvae exposed to low pH had significantly faster development and higher percentage of settlement success compared to control groups. The out-planted juveniles with parental exposure had improved survival and growth compared to juveniles without parental exposure, regardless of the larval exposure history. This implies that transgenerational effects due to parental exposure not only persists but also have a greater influence than the within-generational effects of larval exposure. Our results shed light on the importance of linking the various life history stages when assessing the OA-induced carryover capacity of C. hongkongensis in the natural environment. Understanding these linked relationships helps us better predict the species rapid adaptation responses in the face of changing coastal conditions due to OA.

When site matters: Metabolic and behavioural responses of adult sea urchins from different environments during long-term exposure to seawater acidification

CO₂-driven ocean acidification (OA) affects many aspects of sea urchin biology. However, even in the same species, OA effects are often not univocal due to non-uniform exposure setups or different ecological history of the experimental specimens. In the present work, two groups of adult sea urchins Paracentrotus lividus from different environments (the Lagoon of Venice and a coastal area in the Northern Adriatic Sea) were exposed to OA in a long-term exposure. Animals were maintained for six months in both natural seawater (pH_T 8.04) and end-of-the-century predicted condition (-0.4 units pH). Monthly, physiological (respiration rate, ammonia excretion, O:N ratio) and behavioural (righting, sheltering) endpoints were investigated. Both pH and time of exposure significantly influenced sea urchin responses, but differences between sites were highlighted, particularly in the first months. Under reduced pH, ammonia excretion increased and O:N decreased in coastal specimens. Righting and sheltering were impaired in coastal animals, whereas only righting decreased in lagoon ones. These findings suggested a higher adaptation ability in sea urchins from a more variable environment. Interestingly, as the exposure continued, animals from both sites were able to acclimate. Results revealed plasticity in the physiological and behavioural responses of sea urchins under future predicted OA conditions.

Effects of ocean acidification on acid-base physiology, skeleton properties, and metal contamination in two echinoderms from vent sites in Deception Island, Antarctica

Antarctic surface waters are expected to be the first to experience severe ocean acidification (OA) with carbonate undersaturation and large decreases in pH forecasted before the end of this century. Due to the long stability in environmental conditions and the relatively low daily and seasonal variations to which they are exposed, Antarctic marine organisms, especially those with a supposedly poor machinery to eliminate CO₂ and protons and with a heavily calcified skeleton like echinoderms, are hypothesized as highly vulnerable to these environmental shifts. The opportunities offered by the natural pH gradient generated by vent activities in Deception Island caldera, Western Antarctic Peninsula, were used to investigate for the first time the acid-base physiologies, the impact of OA on the skeleton and the impact of pH on metal accumulation in the Antarctic sea star Odontaster validus and sea urchin Sterechinus neumayeri. The two species were sampled in four stations within the caldera, two at pH (total scale) 8.0-8.1 and two at reduced pH 7.8. Measured variables were pH, alkalinity, and dissolved inorganic carbon of the coelomic fluid; characteristic fracture force, stress and Young's modulus using Weibull statistics and Cd, Cu, Fe, Pb and Zn concentrations in the integument, gonads and digestive system. Recorded acid-base characteristics of both studied species fit in the general picture deduced from temperate and tropical sea stars and sea urchins but conditions and possibly confounding factors, principally food availability and quality, in the studied stations prevented definitive conclusions. Reduced seawater pH 7.8 and metals had almost no impact on the skeleton mechanical properties of the two investigated species despite very high Cd concentrations in O. validus integument. Reduced pH was correlated to increased contamination by most metals but this relation was weak. Translocation and caging experiments taking into account food parameters are proposed to better understand future processes linked to ocean acidification and metal contamination in Antarctic echinoderms.

Sex- and time-specific parental effects of warming on reproduction and offspring quality in a coral reef fish

Global warming can disrupt reproduction or lead to fewer and poorer quality offspring, owing to the thermally sensitive nature of reproductive physiology. However, phenotypic plasticity may enable some animals to adjust the thermal sensitivity of reproduction to maintain performance in warmer conditions. Whether elevated temperature affects reproduction may depend on the timing of exposure to warming and the sex of the parent exposed. We exposed male and female coral reef damselfish (Acanthochromis polyacanthus) during development, reproduction or both life stages to an elevated temperature (+1.5°C) consistent with projected ocean warming and measured reproductive output and newly hatched offspring performance relative to pairs reared in a present-day control temperature. We found female development in elevated temperature increased the probability of breeding, but reproduction ceased if warming continued to the reproductive stage, irrespective of the male's developmental experience. Females that developed in warmer conditions, but reproduced in control conditions, also produced larger eggs and hatchlings with greater yolk reserves. By contrast, male development or pairs reproducing in higher temperature produced fewer and poorer quality offspring. Such changes may be due to alterations in sex hormones or an endocrine stress response. In nature, this could mean female fish developing during a marine heatwave may have enhanced reproduction and produce higher quality offspring compared with females developing in a year of usual thermal conditions. However, male development during a heatwave would likely result in reduced reproductive output. Furthermore, the lack of reproduction from an average increase in temperature could lead to population decline. Our results demonstrate how the timing of exposure differentially influences females and males and how this translates to effects on reproduction and population sustainability in a warming world.

Long-term environmental tolerance of the non-indigenous Pacific oyster to expected contemporary climate change conditions

The current global redistribution of biota is often attributed to two main drivers: contemporary climate change (CCC) and non-indigenous species (NIS). Despite evidence of synergetic effects, however, studies assessing long-term effects of CCC conditions on NIS fitness remain rare. We examined the interactive effects of warming, ocean acidification and reduced salinity on the globally distributed marine NIS Magallana gigas (Pacific oyster) over a ten-month period. Growth, clearance and oxygen consumption rates were measured monthly to assess individual fitness. Lower salinity had a significant, permanent effect on M. gigas, reducing and increasing clearance and oxygen consumption rates, respectively. Neither predicted increases in seawater temperature nor reduced pH had a long-term physiological effect, indicating conditions predicted for 2100 will not affect adult physiology and survival. These results suggest that M. gigas will remain a globally successful NIS and predicted CCC will continue to facilitate their competitive dominance in the near future.

Responses to environmentally relevant microplastics are species-specific with dietary habit as a potential sensitivity indicator

There is a lack of information on understanding how marine organisms respond to environmentally relevant microplastics (MP) which hampers decision making for waste management strategies. This study addresses this information gap by determining whether responses to MPs are species specific within a functional group. Benthic residing sea urchins, Psammechinus miliaris and Paracentrotus lividus were used as a case study. Psammechinus miliaris are strong omnivores with dietary intake including hard components (e.g. shell, tubeworms) and therefore likely to cope with the ingestion of MPs, while P. lividus are strong herbivores consuming softer dietary items (e.g. biofilms, algae) and therefore more likely sensitive. Responses to environmentally relevant MPs were conducted across two trials. Trial one determined the impact of short term (24 h) external exposure to storm-like sediment resuspension of MP concentrations (53 μm polyvinyl chloride (PVC) 25,000 MP L^-1) compared to a control without MPs. No significant impacts were observed for both P. lividus and P. miliaris on metabolic rate or righting time, and urchins were able to remove MPs from the body surface using pedicellariae and cilia. Trial two determined the impact of medium term (2 months) ingestion of a diet laced with PVC MPs (59 μm) at an inclusion rate of 0.5% mass and a control diet (without MPs) on somatic growth and animal condition. The ingestion of MPs did not significantly impact P. miliaris but significantly reduced the alimentary index within P. lividus, indicating a compromised nutritional state. This study shows that responses to microplastics are species-specific and therefore cannot be generalized. Furthermore, feeding habit could act as a potential indicator for sensitivity to MP ingestion which will be important for impact assessments of plastic pollution and management strategies.

Antarctic ecosystems in transition - life between stresses and opportunities

Important findings from the second decade of the 21st century on the impact of environmental change on biological processes in the Antarctic were synthesised by 26 international experts. Ten key messages emerged that have stakeholder-relevance and/or a high impact for the scientific community. They address (i) altered biogeochemical cycles, (ii) ocean acidification, (iii) climate change hotspots, (iv) unexpected dynamism in seabed-dwelling populations, (v) spatial range shifts, (vi) adaptation and thermal resilience, (vii) sea ice related biological fluctuations, (viii) pollution, (ix) endangered terrestrial endemism and (x) the discovery of unknown habitats. Most Antarctic biotas are exposed to multiple stresses and considered vulnerable to environmental change due to narrow tolerance ranges, rapid change, projected circumpolar impacts, low potential for timely genetic adaptation, and migration barriers. Important ecosystem functions, such as primary production and energy transfer between trophic levels, have already changed, and biodiversity patterns have shifted. A confidence assessment of the degree of 'scientific understanding' revealed an intermediate level for most of the more detailed sub-messages, indicating that process-oriented research has been successful in the past decade. Additional efforts are necessary, however, to achieve the level of robustness in scientific knowledge that is required to inform protection measures of the unique Antarctic terrestrial and marine ecosystems, and their contributions to global biodiversity and ecosystem services.

Temperature affects the reproductive outputs of coral-eating starfish Acanthaster spp. after adult exposure to near-future ocean warming and acidification

Outbreaks of the coral-eating crown-of-thorns starfish Acanthaster spp. (COTS) have become to be amongst the most severe threats to coral reefs worldwide. Although most research has focused on COTS early development, it remains unclear how COTS populations will keep pace with changing ocean conditions. Since reproduction is a key process contributing to outbreaks, we investigated the reproductive success of adult COTS acclimated for 3-4 months to different treatment combinations of ambient conditions, ocean warming (+2 °C) and acidification (-0.35 pH). Our results suggest that the optimal breeding season in New Caledonia is concentrated around the end of the calendar year, when water temperature reaches >26 °C. We found negative effects of temperature on egg metrics, fertilisation success, and GSI, conflicting with previously documented effects of temperature on echinoderm reproductive outputs. Fertilisation success dropped drastically (more than threefold) with elevated temperature during the late breeding season. In contrast, we detected no effects of near-future acidification conditions on fertilisation success nor GSI. This is the first time that COTS reproduction is compared among individuals acclimated to different conditions of warming and acidification. Our results highlight the importance of accounting for adult exposure to better understand how COTS reproduction may be impacted in the face of global change.

Do males and females respond differently to ocean acidification? An experimental study with the sea urchin Paracentrotus lividus

Seawater pH lowering, known as ocean acidification, is considered among the major threats to marine environment. In this study, post-spawning adults of the sea urchin Paracentrotus lividus were maintained at three pH values (8.0, 7.7, 7.4) for 60 days. Physiological, biochemical, cellular, behavioural and reproductive responses were evaluated in males and females. Significant differences between sexes were observed, with higher ammonia excretion and lower catalase activity in males. Respiration rate (after 21 days), catalase activity in gonads and total coelomocyte count showed the same increasing trend in males and females under low pH. Ammonia excretion, gonadosomatic index and lysozyme activity exhibited opposite responses to low pH, with an increasing trend in males and decreasing in females. Results demonstrated that exposure to low pH could result in different response strategies of male and female sea urchins at a physiological, biochemical and immunological level. Reduced female gonadosomatic index under low pH suggested decreased energy investment in reproduction.

Molecular mechanisms of biomineralization in marine invertebrates

Much recent marine research has been directed towards understanding the effects of anthropogenic-induced environmental change on marine biodiversity, particularly for those animals with heavily calcified exoskeletons, such as corals, molluscs and urchins. This is because life in our oceans is becoming more challenging for these animals with changes in temperature, pH and salinity. In the future, it will be more energetically expensive to make marine skeletons and the increasingly corrosive conditions in seawater are expected to result in the dissolution of these external skeletons. However, initial predictions of wide-scale sensitivity are changing as we understand more about the mechanisms underpinning skeletal production (biomineralization). These studies demonstrate the complexity of calcification pathways and the cellular responses of animals to these altered conditions. Factors including parental conditioning, phenotypic plasticity and epigenetics can significantly impact the production of skeletons and thus future population success. This understanding is paralleled by an increase in our knowledge of the genes and proteins involved in biomineralization, particularly in some phyla, such as urchins, molluscs and corals. This Review will provide a broad overview of our current understanding of the factors affecting skeletal production in marine invertebrates. It will focus on the molecular mechanisms underpinning biomineralization and how knowledge of these processes affects experimental design and our ability to predict responses to climate change. Understanding marine biomineralization has many tangible benefits in our changing world, including improvements in conservation and aquaculture and exploitation of natural calcified structure design using biomimicry approaches that are aimed at producing novel biocomposites.

Transcriptomes shed light on transgenerational and developmental effects of ocean warming on embryos of the sea urchin Strongylocentrotus intermedius

Ocean warming increasingly endangers the fitness of marine invertebrates. Transgenerational effects (TE) potentially mitigate the impacts of environmental stress on the embryos of marine invertebrates. The molecular mechanisms, however, remain largely unknown. Using high-throughput RNA sequencing technology, we investigated the gene expression patterns of embryos (the gastrula stage) of the sea urchin Strongylocentrotus intermedius at different developmental temperatures, whose parents were exposed to long-term (15 months) elevated temperature (A) or not (B). The temperatures at which adults were held for ~4 weeks prior to the start of the experiment (21 °C for A and 18 °C for B) were also used for the development of offspring (high: 21 °C and ambient (laboratory): 18 °C) resulting in four experimental groups (HA and HB at 21 °C, and LA and LB at 18 °C). The embryos were sampled ~24 h after fertilization. All samples were in the gastrula stage. Twelve mRNA libraries (groups HA, HB, LA, LB, 3 replicates for each group) were established for the following sequencing. Embryos whose parents were exposed to elevated temperatures or not showed 1891 significantly different DEGs (differentially expressed genes) at the ambient developmental temperature (LB vs LA, LB as control) and 2203 significantly different DEGs at the high developmental temperature (HB vs HA, HB as control), respectively. This result indicates complex molecular mechanisms of transgenerational effects of ocean warming, in which a large number of genes are involved. With the TE, we found 904 shared DEGs in both LB vs LA (LB as control) and HB vs HA (HB as control) changed in the same direction of expression (i.e., up- or down-regulated), indicating that parental exposed temperatures affect the expression of these genes in the same manner regardless of the development temperature. With developmental exposure, we found 198 shared DEGs in both HB vs LB (HB as control) and HA vs LA (HA as control) changed in the same direction of expression. Of the 198 DEGs, more genes were up-regulated at high developmental temperature. Interestingly, embryos whose parents were exposed to high temperature showed fewer differently expressed DEGs between high and low developmental temperatures than the individuals whose parents were exposed to ambient temperature. The results indicate that gene expressions are probably depressed by the transgenerational effect of ocean warming. The roles of hsp70 and hnf6 in thermal acclimation are highlighted for future studies. The present study provides new insights into the molecular mechanisms of the transgenerational and developmental effects of ocean warming on the embryos of sea urchins.

Effects of ocean acidification on Antarctic marine organisms: A meta-analysis

Southern Ocean waters are among the most vulnerable to ocean acidification. The projected increase in the CO2 level will cause changes in carbonate chemistry that are likely to be damaging to organisms inhabiting these waters. A meta-analysis was undertaken to examine the vulnerability of Antarctic marine biota occupying waters south of 60°S to ocean acidification. This meta-analysis showed that ocean acidification negatively affects autotrophic organisms, mainly phytoplankton, at CO2 levels above 1,000 μatm and invertebrates above 1,500 μatm, but positively affects bacterial abundance. The sensitivity of phytoplankton to ocean acidification was influenced by the experimental procedure used. Natural, mixed communities were more sensitive than single species in culture and showed a decline in chlorophyll a concentration, productivity, and photosynthetic health, as well as a shift in community composition at CO2 levels above 1,000 μatm. Invertebrates showed reduced fertilization rates and increased occurrence of larval abnormalities, as well as decreased calcification rates and increased shell dissolution with any increase in CO2 level above 1,500 μatm. Assessment of the vulnerability of fish and macroalgae to ocean acidification was limited by the number of studies available. Overall, this analysis indicates that many marine organisms in the Southern Ocean are likely to be susceptible to ocean acidification and thereby likely to change their contribution to ecosystem services in the future. Further studies are required to address the poor spatial coverage, lack of community or ecosystem-level studies, and the largely unknown potential for organisms to acclimate and/or adapt to the changing conditions.

Metabolic recovery and compensatory shell growth of juvenile Pacific geoduck Panopea generosa following short-term exposure to acidified seawater

While acute stressors can be detrimental, environmental stress conditioning can improve performance. To test the hypothesis that physiological status is altered by stress conditioning, we subjected juvenile Pacific geoduck, Panopea generosa, to repeated exposures of elevated pCO₂ in a commercial hatchery setting followed by a period in ambient common garden. Respiration rate and shell length were measured for juvenile geoduck periodically throughout short-term repeated reciprocal exposure periods in ambient (~550 μatm) or elevated (~2400 μatm) pCO₂ treatments and in common, ambient conditions, 5 months after exposure. Short-term exposure periods comprised an initial 10-day exposure followed by 14 days in ambient before a secondary 6-day reciprocal exposure. The initial exposure to elevated pCO₂ significantly reduced respiration rate by 25% relative to ambient conditions, but no effect on shell growth was detected. Following 14 days in common garden, ambient conditions, reciprocal exposure to elevated or ambient pCO₂ did not alter juvenile respiration rates, indicating ability for metabolic recovery under subsequent conditions. Shell growth was negatively affected during the reciprocal treatment in both exposure histories; however, clams exposed to the initial elevated pCO₂ showed compensatory growth with 5.8% greater shell length (on average between the two secondary exposures) after 5 months in ambient conditions. Additionally, clams exposed to the secondary elevated pCO₂ showed 52.4% increase in respiration rate after 5 months in ambient conditions. Early exposure to low pH appears to trigger carryover effects suggesting bioenergetic re-allocation facilitates growth compensation. Life stage-specific exposures to stress can determine when it may be especially detrimental, or advantageous, to apply stress conditioning for commercial production of this long-lived burrowing clam.

Short-Term Exposure to Storm-Like Scenario Microplastic and Salinity Conditions Does not Impact Adult Sea Urchin (Arbacia punctulata) Physiology

The effects of microplastic pollution on sea urchins has received little attention despite their ecological and economical importance. This is the first study to focus on adult sea urchins (Arbacia punctulata). These organisms were exposed to storm-like sediment resuspension of microplastic concentrations (9-μm polystyrene 25,000 spheres L^-1) combined with salinity reductions (salinity 25 vs. 33) associated with high precipitation. Urchins were exposed to these parameters for 24 h before assessing righting times and for 48 h before assessing oxygen consumption rates. No significant impacts on urchin physiology were observed showing resilience to short-term exposures of storm-like induced microplastics and salinity. No microplastic particles blocked the madreporite pores indicating the active removal of particles by cilia and pedicellariae. Gut tissue samples indicated consumption of microplastics. Studies on more species are urgently required to determine their responses to plastic pollution to inform management decision-making processes.

Elevated pCO2 does not impair performance in autotomised individuals of the intertidal predatory starfish Asterias rubens (Linnaeus, 1758)

The impacts of ocean acidification remain less well-studied in starfish compared to other echinoderm groups. This study examined the combined effects of elevated pCO2 and arm regeneration on the performance of the intertidal predatory starfish Asterias rubens, as both are predicted to come at a cost to the individual. A two-way factorial experiment (~400 μatm vs ~1000 μatm; autotomised vs non-automised individuals) was used to examine growth rates, lipid content (pyloric caeca and gonads), and calcium content (body wall) in both intact and regenerating arms, as well as subsequent effects on rate of arm regeneration, righting time (behaviour) and mortality over 120 days. Autotomised individuals tended to show lower (not significant), survival and growth. Elevated pCO2 had no effect on mortality, body growth, arm regeneration, righting time or arm calcium content. Lipid content was higher in the pyloric caeca, but not in the gonads, in response to elevated pCO2 irrespective of autotomisation. The results of the study suggest that adult A. rubens remain unaffected by increased pCO2 and/or arm autotomy for 120 days, although longer term experiments are necessary as the results indicated that survival, growth and calcification may be impaired with longer-term exposure to elevated pCO2.

Temporal variability modulates pH impact on larval sea urchin development: Themed Issue Article: Biomechanics and Climate Change

Coastal organisms reside in highly dynamic habitats. Global climate change is expected to alter not only the mean of the physical conditions experienced but also the frequencies and/or the magnitude of fluctuations of environmental factors. Understanding responses in an ecologically relevant context is essential for formulating management strategies. In particular, there are increasing suggestions that exposure to fluctuations could alleviate the impact of climate change-related stressors by selecting for plasticity that may help acclimatization to future conditions. However, it remains unclear whether the presence of fluctuations alone is sufficient to confer such effects or whether the pattern of the fluctuations matters. Therefore, we investigated the role of frequency and initial conditions of the fluctuations on performance by exposing larval sea urchin Heliocidaris crassispina to either constant or fluctuating pH. Reduced pH alone (pH 7.3 vs 8.0) did not affect larval mortality but reduced the growth of larval arms in the static pH treatments. Changes in morphology could affect the swimming mechanics for these small organisms, and geometric morphometric analysis further suggested an overall shape change such that acidified larvae had more U-shaped bodies and shorter arms, which would help maintain stability in moving water. The relative negative impact of lower pH, computed as log response ratio, on larval arm development was smaller when larvae were exposed to pH fluctuations, especially when the change was less frequent (48- vs 24-h cycle). Furthermore, larvae experiencing an initial pH drop, i.e. those where the cycle started at pH 8.0, were more negatively impacted compared with those kept at an initial pH of 7.3 before the cycling started. Our observations suggest that larval responses to climate change stress could not be easily predicted from mean conditions. Instead, to better predict organismal performance in the future ocean, monitoring and investigation of the role of real-time environmental fluctuations along the dispersive pathway is key.

Limitations of cross- and multigenerational plasticity for marine invertebrates faced with global climate change

Although cross generation (CGP) and multigenerational (MGP) plasticity have been identified as mechanisms of acclimation to global change, the weight of evidence indicates that parental conditioning over generations is not a panacea to rescue stress sensitivity in offspring. For many species, there were no benefits of parental conditioning. Even when improved performance was observed, this waned over time within a generation or across generations and fitness declined. CGP and MGP studies identified resilient species with stress tolerant genotypes in wild populations and selected family lines. Several bivalves possess favourable stress tolerance and phenotypically plastic traits potentially associated with genetic adaptation to life in habitats where they routinely experience temperature and/or acidification stress. These traits will be important to help 'climate proof' shellfish ventures. Species that are naturally stress tolerant and those that naturally experience a broad range of environmental conditions are good candidates to provide insights into the physiological and molecular mechanisms involved in CGP and MGP. It is challenging to conduct ecologically relevant global change experiments over the long times commensurate with the pace of changing climate. As a result, many studies present stressors in a shock-type exposure at rates much faster than projected scenarios. With more gradual stressor introduction over longer experimental durations and in context with conditions species are currently acclimatized and/or adapted to, the outcomes for sensitive species might differ. We highlight the importance to understand primordial germ cell development and the timing of gametogenesis with respect to stressor exposure. Although multigenerational exposure to global change stressors currently appears limited as a universal tool to rescue species in the face of changing climate, natural proxies of future conditions (upwelling zones, CO₂ vents, naturally warm habitats) show that phenotypic adjustment and/or beneficial genetic selection is possible for some species, indicating complex plasticity-adaptation interactions.

Warm temperatures, cool sponges: the effect of increased temperatures on the Antarctic sponge Isodictya sp

Although the cellular and molecular responses to exposure to relatively high temperatures (acute thermal stress or heat shock) have been studied previously, only sparse empirical evidence of how it affects cold-water species is available. As climate change becomes more pronounced in areas such as the Western Antarctic Peninsula, both long-term and occasional acute temperature rises will impact species found there, and it has become crucial to understand the capacity of these species to respond to such thermal stress. Here, we use the Antarctic sponge Isodictya sp. to investigate how sessile organisms (particularly Porifera) can adjust to acute short-term heat stress, by exposing this species to 3 and 5 °C for 4 h, corresponding to predicted temperatures under high-end 2080 IPCC-SRES scenarios. Assembling a de novo reference transcriptome (90,188 contigs, >93.7% metazoan BUSCO genes) we have begun to discern the molecular response employed by Isodictya to adjust to heat exposure. Our initial analyses suggest that TGF-β, ubiquitin and hedgehog cascades are involved, alongside other genes. However, the degree and type of response changed little from 3 to 5 °C in the time frame examined, suggesting that even moderate rises in temperature could cause stress at the limits of this organism’s capacity. Given the importance of sponges to Antarctic ecosystems, our findings are vital for discerning the consequences of short-term increases in Antarctic ocean temperature on these and other species.

Transgenerational Plasticity in Human-Altered Environments

Our ability to predict how species will respond to human-induced rapid environmental change (HIREC) may depend upon our understanding of transgenerational plasticity (TGP), which occurs when environments experienced by previous generations influence phenotypes of subsequent generations. TGP evolved to help organisms cope with environmental stressors when parental environments are highly predictive of offspring environments. HIREC can alter conditions that favored TGP in historical environments by reducing parents' ability to detect environmental conditions, disrupting previous correlations between parental and offspring environments, and interfering with the transmission of parental cues to offspring. Because of the propensity to produce errors in these processes, TGP will likely generate negative fitness outcomes in response to HIREC, though beneficial fitness outcomes may occur in some cases.

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; pHT: 7.7, 7.4; control: 17°C-pHT7.9) 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 pHT7.7 while in the extreme treatment (21°C-pHT7.4) 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-pHT7.4 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.

Assessing the impact of elevated pCO2 within and across generations in a highly invasive fouling mussel (Musculista senhousia)

Marine biofouling by the swiftly spreading invasive mussel (Musculista senhousia) has caused serious ecological and economic consequences in the global coastal waters. However, the fate of this highly invasive fouling species in a rapidly acidifying ocean remains unknown. Here, we demonstrated the impacts of ocean acidification within and across generations, to understand whether M. senhousia has the capacity to acclimate to changing ocean conditions. During the gonadal development, exposure of mussels to elevated pCO₂ caused significant decreases of survival, growth performance and condition index, and shifted the whole-organism energy budget by inflating energy expenses to fuel compensatory processes, eventually impairing the success of spawning. Yet, rapid transgenerational acclimation occurred during the early life history stage and persisted into adulthood. Eggs spawned from CO₂-exposed mussels were significantly bigger compared with those from non-CO₂-exposed mussels, indicating increased maternal provisioning into eggs and hence conferring larvae resilience under harsh conditions. Larvae with a prior history of transgenerational exposure to elevated pCO₂ developed faster and had a higher survival than those with no prior history of CO₂ exposure. Transgenerational exposure significantly increased the number of larvae completing metamorphosis. While significant differences in shell growth were no longer observed during juvenile nursery and adult grow-out, transgenerationally exposed mussels displayed improved survival in comparison to non-transgenerationally exposed mussels. Metabolic plasticity arose following transgenerational acclimation, generating more energy available for fitness-related functions. Overall, the present study demonstrates the remarkable ability of M. senhousia to respond plastically and acclimate rapidly to changing ocean conditions.

Antarctic environmental change and biological responses

Antarctica and the surrounding Southern Ocean are facing complex environmental change. Their native biota has adapted to the region's extreme conditions over many millions of years. This unique biota is now challenged by environmental change and the direct impacts of human activity. The terrestrial biota is characterized by considerable physiological and ecological flexibility and is expected to show increases in productivity, population sizes and ranges of individual species, and community complexity. However, the establishment of non-native organisms in both terrestrial and marine ecosystems may present an even greater threat than climate change itself. In the marine environment, much more limited response flexibility means that even small levels of warming are threatening. Changing sea ice has large impacts on ecosystem processes, while ocean acidification and coastal freshening are expected to have major impacts.

Transgenerational effects of UV-B radiation on egg size, fertilization, hatching and larval size of sea urchins Strongylocentrotus intermedius

Transgenerational effects are important for phenotypic plasticity and adaptation of marine invertebrates in the changing ocean. Ultraviolet-B (UV-B) radiation is an increasing threat to marine invertebrates. For the first time, we reported positive and negative transgenerational effects of UV-B radiation on egg size, fertilization, hatchability and larval size of a marine invertebrate. Strongylocentrotus intermedius exposed to UV-B radiation showed positive transgenerational effects and adaptation on egg size, hatching rate and post-oral arm length of larvae. Negative transgenerational effects were found in body length, stomach length and stomach width of larvae whose parents were exposed to UV-B radiation. Sires probably play important roles in transgenerational effects of UV-B. The present study provides valuable information into transgenerational effects of UV-B radiation on fitness related traits of sea urchins (at least Strongylocentrotus intermedius).

Robustness of Adamussium colbecki shell to ocean acidification in a short-term exposure

Atmospheric pCO₂ has increased since the industrial revolution leading to a lowering of the ocean surface water pH, a phenomenon called ocean acidification (OA). OA is claimed to be a major threat for marine organisms and ecosystems and, particularly, for Polar regions. We explored the impact of OA on the shell mechanical properties of the Antarctic scallop Adamussium colbecki exposed for one month to acidified (pH 7.6) and natural conditions (unmanipulated littoral water), by performing Scanning Electron Microscopy, nanoindentation and Vickers indentation on the scallop shell. No effect of pH could be detected either in crystal deposition or in the mechanical properties. A. colbecki shell was found to be resistant to OA, which suggests this species to be able to face a climate change scenario that may threat the persistence of the endemic Antarctic species. Further investigation should be carried out in order to elucidate the destiny of this key species in light of global change.

Lack of long-term acclimation in Antarctic encrusting species suggests vulnerability to warming

Marine encrusting communities play vital roles in benthic ecosystems and have major economic implications with regards to biofouling. However, their ability to persist under projected warming scenarios remains poorly understood and is difficult to study under realistic conditions. Here, using heated settlement panel technologies, we show that after 18 months Antarctic encrusting communities do not acclimate to either +1 °C or +2 °C above ambient temperatures. There is significant up-regulation of the cellular stress response in warmed animals, their upper lethal temperatures decline with increasing ambient temperature and population genetic analyses show little evidence of differential survival of genotypes with treatment. By contrast, biofilm bacterial communities show no significant differences in community structure with temperature. Thus, metazoan and bacterial responses differ dramatically, suggesting that ecosystem responses to future climate change are likely to be far more complex than previously anticipated.

Genetic adaptation and physiological acclimation can potentially buffer species against climate change. Here, the authors perform a long-term warming experiment of Antarctic encrusting communities and show that focal animal species failed to acclimate and lacked genetic variation in tolerance to warming.

Impacts of ocean acidification on sea urchin growth across the juvenile to mature adult life-stage transition is mitigated by warming

Understanding how growth trajectories of calcifying invertebrates are affected by changing climate requires acclimation experiments that follow development across life-history transitions. In a long-term acclimation study, the effects of increased acidification and temperature on survival and growth of the tropical sea urchin Tripneustes gratilla from the early juvenile (5 mm test diameter-TD) through the developmental transition to the mature adult (60 mm TD) were investigated. Juveniles were reared in a combination of three temperature and three pH/pCO₂ treatments, including treatments commensurate with global change projections. Elevated temperature and pCO₂/pH both affected growth, but there was no interaction between these factors. The urchins grew more slowly at pH 7.6, but not at pH 7.8. Slow growth may be influenced by the inability to compensate coelomic fluid acid-base balance at pH 7.6. Growth was faster at +3 and +6°C compared to that in ambient temperature. Acidification and warming had strong and interactive effects on reproductive potential. Warming increased the gonad index, but acidification decreased it. At pH 7.6 there were virtually no gonads in any urchins regardless of temperature. The T. gratilla were larger at maturity under combined near-future warming and acidification scenarios (+3°C/pH 7.8). Although the juveniles grew and survived in near-future warming and acidification conditions, chronic exposure to these stressors from an early stage altered allocation to somatic and gonad growth. In the absence of phenotypic adjustment, the interactive effects of warming and acidification on the benthic life phases of sea urchins may compromise reproductive fitness and population maintenance as global climatic change unfolds.

Thicker Shells Compensate Extensive Dissolution in Brachiopods under Future Ocean Acidification

Organisms with long generation times require phenotypic plasticity to survive in changing environments until genetic adaptation can be achieved. Marine calcifiers are particularly vulnerable to ocean acidification due to dissolution and a reduction in shell-building carbonate ions. Long-term experiments assess organisms' abilities to acclimatize or even adapt to environmental change. Here we present an unexpected compensatory response to extensive shell dissolution in a highly calcium-carbonate-dependent organism after long-term culture in predicted end-century acidification and warming conditions. Substantial shell dissolution with decreasing pH posed a threat to both a polar ( Liothyrella uva) and a temperate ( Calloria inconspicua) brachiopod after 7 months and 3 months exposure, respectively, with more extensive dissolution in the polar species. This impact was reflected in decreased outer primary layer thickness in the polar brachiopod. A compensatory response of increasing inner secondary layer thickness, and thereby producing a thicker shell, was exhibited by the polar species. Less extensive dissolution in the temperate brachiopod did not affect shell thickness. Increased temperature did not impact shell dissolution or thickness. Brachiopod ability to produce a thicker shell when extensive shell dissolution occurs suggests this marine calcifier has great plasticity in calcification providing insights into how similar species might cope under future environmental change.

The impact of ocean acidification on the gonads of three key Antarctic benthic macroinvertebrates

CO₂ atmospheric pressure is increasing since industrial revolution, leading to a lowering of the ocean surface water pH, a phenomenon known as ocean acidification, with several reported effects on individual species and cascading effects on marine ecosystems. Despite the great amount of literature on ocean acidification effects on calcifying organisms, the response of their reproductive system still remains poorly known. In the present study, we investigated the histopathological effects of low pH on the gonads of three key macroinvertebrates of the Terra Nova Bay (Ross Sea) littoral area: the sea urchin Sterechinus neumayeri, the sea star Odontaster validus and the scallop Adamussium colbecki. After 1 month of exposure at control (8.12) and reduced (7.8 and 7.6) pH levels, we dissected the gonads and performed histological analyses to detect potential differences among treatments. Results showed significant effects on reproductive conditions of A. colbecki and S. neumayeri, while O. validus did not show any kind of alteration. Present results reinforce the need to focus on ocean acidification effects on soft tissues, particularly the gonads, whose damage may exert large effects on the individual fitness, with cascading effects on the population dynamic of the species.

Molecular mechanisms underpinning transgenerational plasticity in the green sea urchin Psammechinus miliaris

The pre-conditioning of adult marine invertebrates to altered conditions, such as low pH, can significantly impact offspring outcomes, a process which is often referred to as transgenerational plasticity (TGP). This study describes for the first time, the gene expression profiles associated with TGP in the green sea urchin Psammechinus miliaris and evaluates the transcriptional contribution to larval resilience. RNA-Seq was used to determine how the expression profiles of larvae spawned into low pH from pre-acclimated adults differed to those of larvae produced from adults cultured under ambient pH. The main findings demonstrated that adult conditioning to low pH critically pre-loads the embryonic transcriptional pool with antioxidants to prepare the larvae for the “new” conditions. In addition, the classic cellular stress response, measured via the production of heat shock proteins (the heat shock response (HSR)), was separately evaluated. None of the early stage larvae either spawned in low pH (produced from both ambient and pre-acclimated adults) or subjected to a separate heat shock experiment were able to activate the full HSR as measured in adults, but the capacity to mount an HSR increased as development proceeded. This compromised ability clearly contributes to the vulnerability of early stage larvae to acute environmental challenge.