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

Effects of seawater acidification and warming on morphometrics and biomineralization-related gene expression during embryo-larval development of a lightly-calcified echinoderm

CO2-induced ocean acidification and warming pose ecological threats to marine life, especially calcifying species such as echinoderms, who rely on biomineralization for skeleton formation. However, previous studies on echinoderm calcification amid climate change had a strong bias towards heavily calcified echinoderms, with little research on lightly calcified ones, such as sea cucumbers. Here, we analyzed the embryo-larval development and their biomineralization-related gene expression of a lightly calcified echinoderm, the sea cucumber (Apostichopus japonicus), under experimental seawater acidification (OA) and/or warming (OW). Results showed that OA (- 0.37 units) delayed development and decreased body size (8.58-56.25 % and 0.36-19.66 % decreases in stage duration and body length, respectively), whereas OW (+3.1 °C) accelerated development and increased body size (33.99-55.28 % increase in stage duration and 2.44-14.41 % enlargement in body length). OW buffered the negative effects of OA on the development timing and body size of A. japonicus. Additionally, no target genes were expressed in the blastula stage, and only two biomineralization genes (colp3α, cyp2) and five TFs (erg, tgif, foxN2/3, gata1/2/3, and tbr) were expressed throughout the embryo-larval development. Our findings suggest that the low calcification in A. japonicus larvae may be caused by biomineralization genes contraction, and low expression of those genes. Furthermore, this study indicated that seawater acidification and warming affect expression of biomineralization-related genes, and had an effect on body size and development rate during the embryo-larval stage in sea cucumbers. Our study is a first step toward a better understanding of the complexity of high pCO2 on calcification and helpful for revealing the adaptive strategy of less-calcified echinoderms amid climate change.

Interactive effects of chronic ocean acidification and warming on the growth, survival, and physiological responses of adults of the temperate sea urchin Strongylocentrotusintermedius

To investigate the interactive effects of chronic ocean acidification and warming (OAW) on the growth, survival, and physiological responses of sea urchins, adults of the temperate sea urchin Strongylocentrotus intermedius were incubated separately/jointly in acidic (ΔpHNBS = -0.5 units) and thermal (ΔT = +3.0 °C) seawater for 120 days under lab-controlled conditions based on the projected ocean pH and temperature for 2100 put forward by the Intergovernmental Panel on Climate Change (IPCC). Survival rate (SR), average food consumption rate (FCR), gut index (GuI), specific growth rate (SGR), digestive capability, energy production, and antioxidant capability were subsequently determined. The results showed that 1) the SR, FCR, GuI and SGR decreased sharply under OAW conditions. Significant interactive effects of OAW on SR and SGR were observed at 120 days post-incubation (dpi), and on FCR this occurred at 90 dpi. 2) OAW altered the activities of both digestive and antioxidant enzymes. There were significant interaction effects of OAW on the activities of amylase, trehalase, and superoxide dismutase. 3) The relative gene expression levels and activities of key enzymes involved in glycometabolism pathways (i.e., glycolysis and the tricarboxylic acid cycle) were significantly affected by OAW, resulting in an alteration of the total ATP content in the sea urchins. Interaction effects of OAW were observed in both relative gene expression and the activity of enzymes involved in glycolysis (hexokinase), the transformation of glycolysis end-products (lactate dehydrogenase), the tricarboxylic acid cycle (citrate synthetase), and ATP production (Na+/K+-ATPase). The data from this study will enrich our knowledge concerning the combined effects of global climate change on the survival, growth, and physiological responses of echinoderms.

Transcriptomic Responses of a Lightly Calcified Echinoderm to Experimental Seawater Acidification and Warming during Early Development

Ocean acidification (OA) and ocean warming (OW) are potential obstacles to the survival and growth of marine organisms, particularly those that rely on calcification. This study investigated the single and joint effects of OA and OW on sea cucumber Apostichopus japonicus larvae raised under combinations of two temperatures (19 °C or 22 °C) and two pCO2 levels (400 or 1000 μatm) that reflect the current and end-of-21st-century projected ocean scenarios. The investigation focused on assessing larval development and identifying differences in gene expression patterns at four crucial embryo-larval stages (blastula, gastrula, auricularia, and doliolaria) of sea cucumbers, using RNA-seq. Results showed the detrimental effect of OA on the early development and body growth of A. japonicus larvae and a reduction in the expression of genes associated with biomineralization, skeletogenesis, and ion homeostasis. This effect was particularly pronounced during the doliolaria stage, indicating the presence of bottlenecks in larval development at this transition phase between the larval and megalopa stages in response to OA. OW accelerated the larval development across four stages of A. japonicus, especially at the blastula and doliolaria stages, but resulted in a widespread upregulation of genes related to heat shock proteins, antioxidant defense, and immune response. Significantly, the negative effects of elevated pCO2 on the developmental process of larvae appeared to be mitigated when accompanied by increased temperatures at the expense of reduced immune resilience and increased system fragility. These findings suggest that alterations in gene expression within the larvae of A. japonicus provide a mechanism to adapt to stressors arising from a rapidly changing oceanic environment.

Juvenile waiting stage crown-of-thorns sea stars are resilient in heatwave conditions that bleach and kill corals

The juveniles of predatory sea stars can remain in their recruitment-nursery habitat for some time before their ontogenetic shift to the adult habitat and diet. These small juveniles are vulnerable to a range of factors with their sensitivity amplified by climate change-driven ocean warming. We investigate the thermal tolerance of the waiting stage herbivorous juveniles of the keystone coral predator, the crown-of-thorns sea star (COTS, Acanthaster sp.), in context with the degree heating weeks (DHW) model that predicts coral bleaching and mass mortality. In temperature treatments ranging from +1 to 3°C in prolonged heatwave acclimation conditions, the juveniles exhibited ~100% survival in DHW scenarios that trigger coral bleaching (4 DHW), resulting in mass mortality of corals (8 DHW) and extreme conditions well beyond those that kill corals (12 DHW). This indicates that herbivorous juvenile COTS are far more resistant to heatwave conditions than the coral prey of the adults. The juveniles exhibited higher activity (righting) and metabolic rate after weeks in increased temperature. In separate acute temperature experiments, the upper thermal limit of the juveniles was 34-36°C. In a warming world, juvenile COTS residing in their coral rubble nursery habitat will benefit from an increase in the extent of this habitat due to coral mortality. The juveniles have potential for long-term persistence as herbivores as they wait for live coral to recover before becoming coral predators, thereby serving as a proximate source of COTS outbreaks on reefs already in a tenuous state due to climate change.

Impacts of ocean warming on echinoderms: A meta-analysis

Rising ocean temperatures are threatening marine species and populations worldwide, and ectothermic taxa are particularly vulnerable. Echinoderms are an ecologically important phylum of marine ectotherms and shifts in their population dynamics can have profound impacts on the marine environment. The effects of warming on echinoderms are highly variable across controlled laboratory-based studies. Accordingly, synthesis of these studies will facilitate the better understanding of broad patterns in responses of echinoderms to ocean warming. Herein, a meta-analysis incorporating the results of 85 studies (710 individual responses) is presented, exploring the effects of warming on various performance predictors. The mean responses of echinoderms to all magnitudes of warming were compared across multiple biological responses, ontogenetic life stages, taxonomic classes, and regions, facilitated by multivariate linear mixed effects models. Further models were conducted, which only incorporated responses to warming greater than the projected end-of-century mean annual temperatures at the collection sites. This meta-analysis provides evidence that ocean warming will generally accelerate metabolic rate (+32%) and reduce survival (-35%) in echinoderms, and echinoderms from subtropical (-9%) and tropical (-8%) regions will be the most vulnerable. The relatively high vulnerability of echinoderm larvae to warming (-20%) indicates that this life stage may be a significant developmental bottleneck in the near-future, likely reducing successful recruitment into populations. Furthermore, asteroids appear to be the class of echinoderms that are most negatively affected by elevated temperature (-30%). When considering only responses to magnitudes of warming representative of end-of-century climate change projections, the negative impacts on asteroids, tropical species and juveniles were exacerbated (-51%, -34% and -40% respectively). The results of these analyses enable better predictions of how keystone and invasive echinoderm species may perform in a warmer ocean, and the possible consequences for populations, communities and ecosystems.

The effects of temperature and pH on the reproductive ecology of sand dollars and sea urchins: Impacts on sperm swimming and fertilization

In an era of climate change, impacts on the marine environment include warming and ocean acidification. These effects can be amplified in shallow coastal regions where conditions often fluctuate widely. This type of environmental variation is potentially important for many nearshore species that are broadcast spawners, releasing eggs and sperm into the water column for fertilization. We conducted two experiments to investigate: 1) the impact of water temperature on sperm swimming characteristics and fertilization rate in sand dollars (Dendraster excentricus; temperatures 8-38°C) and sea urchins (Mesocentrotus franciscanus; temperatures 8-28°C) and; 2) the combined effects of multiple stressors (water temperature and pH) on these traits in sand dollars. We quantify thermal performance curves showing that sand dollar fertilization rates, sperm swimming velocities, and sperm motility display remarkably wide thermal breadths relative to red urchins, perhaps reflecting the wider range of water temperatures experienced by sand dollars at our field sites. For sand dollars, both temperature (8, 16, 24°C) and pH (7.1, 7.5, 7.9) affected fertilization but only temperature influenced sperm swimming velocity and motility. Although sperm velocities and fertilization were positively correlated, our fertilization kinetics model dramatically overestimated measured rates and this discrepancy was most pronounced under extreme temperature and pH conditions. Our results suggest that environmental stressors like temperature and pH likely impair aspects of the reproductive process beyond simple sperm swimming behavior.

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.

Effects of Seawater Acidification on Echinoid Adult Stage: A Review

The continuous release of CO2 in the atmosphere is increasing the acidity of seawater worldwide, and the pH is predicted to be reduced by ~0.4 units by 2100. Ocean acidification (OA) is changing the carbonate chemistry, jeopardizing the life of marine organisms, and in particular calcifying organisms. Because of their calcareous skeleton and limited ability to regulate the acid–base balance, echinoids are among the organisms most threatened by OA. In this review, 50 articles assessing the effects of seawater acidification on the echinoid adult stage have been collected and summarized, in order to identify the most important aspects to consider for future experiments. Most of the endpoints considered (i.e., related to calcification, physiology, behaviour and reproduction) were altered, highlighting how various and subtle the effects of pH reduction can be. In general terms, more than 43% of the endpoints were modified by low pH compared with the control condition. However, animals exposed in long-term experiments or resident in CO2-vent systems showed acclimation capability. Moreover, the latitudinal range of animals’ distribution might explain some of the differences found among species. Therefore, future experiments should consider local variability, long-term exposure and multigenerational approaches to better assess OA effects on echinoids.

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.

Combined effect of microplastics and global warming factors on early growth and development of the sea urchin (Paracentrotus lividus)

The aim of this work was to estimate the potential risk of the combined effect of global change factors (acidification, temperature increase) and microplastic (MP) pollution on the growth and development of the sea urchin P. lividus. Embryo-larval bioassays were conducted to determine growth and morphology after 48 h of incubation with MP (1000 and 3000 particles/mL); with filtered sea water at pH = 7.6; and with their combinations. A second experiment was conducted to study the effect of pH and MP in combination with a temperature increase of 4 °C compared to control (20 °C). We found that the inhibition of growth in embryos reared at pH = 7.6 was around 75%. Larvae incubated at 3000 MP particles/mL showed a 20% decrease in growth compared to controls. The exposure to MP also induced an increase in the postoral arm separation or rounded vertices. The combined exposure to a pH 7.6 and MP caused a significant decrease of larval growth compared to control, to MP and to pH 7.6 treatments. Morphological alterations were observed in these treatments, including the development of only two arms. Increasing the temperature resulted in an increased growth in control, in pH 7.6 and pH 7.6 + MP3000 treatments, but the relative stomach volume decreased. However, when growth parameters were expressed per Degree-Days the lower growth provoked by the thermal stress was evidenced in all treatments. In this work we demonstrated that MP could aggravate the effect of a decreased pH and that an increase in water temperature generated an additional stress on P. lividus larvae, manifested in a lower growth and an altered development. Therefore, the combined stress caused by ocean warming, ocean acidification, and microplastic pollution, could threaten sea urchin populations leading to a potential impact on coastal ecosystems.

Effects of marine heatwave conditions across the metamorphic transition to the juvenile sea urchin (Heliocidaris erythrogramma)

For short development species, like the sea urchin Heliocidaris erythrogramma, the entire planktonic duration can be impacted by marine heatwaves (MHW). Developmental thermal tolerance of this species through metamorphosis was investigated over a broad range (7.6-28.0 °C), including temperatures across its distribution and MHW conditions. In controls (19.5-21.0 °C), 80% of individuals developed to metamorphosis at day 5, doubling to 10 days at 14.0 °C. The thermal range (14.4-21.2 °C) of metamorphosis on day 7 reflected the realised thermal niche with 25.9 °C the upper temperature for success (T₄₀). By day 10, juvenile tolerance narrowed to the local range (16.2-19.0 °C), similar to levels tolerated by adults, indicating negative carryover effects across the metamorphic transition. Without phenotypic adjustment or adaptation, regional warming will be detrimental, although populations may be sustained by thermotolerant offspring. Our results show the importance of the metamorphic transition in understanding the cumulative sensitivity of species to MHW.

Ocean acidification induces distinct transcriptomic responses across life history stages of the sea urchin Heliocidaris erythrogramma

Ocean acidification (OA) from seawater uptake of rising carbon dioxide emissions impairs development in marine invertebrates, particularly in calcifying species. Plasticity in gene expression is thought to mediate many of these physiological effects, but how these responses change across life history stages remains unclear. The abbreviated lecithotrophic development of the sea urchin Heliocidaris erythrogramma provides a valuable opportunity to analyse gene expression responses across a wide range of life history stages, including the benthic, post-metamorphic juvenile. We measured the transcriptional response to OA in H. erythrogramma at three stages of the life cycle (embryo, larva, and juvenile) in a controlled breeding design. The results reveal a broad range of strikingly stage-specific impacts of OA on transcription, including changes in the number and identity of affected genes; the magnitude, sign, and variance of their expression response; and the developmental trajectory of expression. The impact of OA on transcription was notably modest in relation to gene expression changes during unperturbed development and much smaller than genetic contributions from parentage. The latter result suggests that natural populations may provide an extensive genetic reservoir of resilience to OA. Taken together, these results highlight the complexity of the molecular response to OA, its substantial life history stage specificity, and the importance of contextualizing the transcriptional response to pH stress in light of normal development and standing genetic variation to better understand the capacity for marine invertebrates to adapt to OA.

Decreased pH impairs sea urchin resistance to predatory fish: A combined laboratory-field study to understand the fate of top-down processes in future oceans

Changing oceans represent a serious threat for a wide range of marine organisms, with severe cascading effects on ecosystems and their services. Sea urchins are particularly sensitive to decreased pH expected for the end of the century and their key ecological role in regulating community structure and functioning could be seriously compromised. An integrated approach of laboratory and field experiments has been implemented to investigate the effects of decreased pH on predator-prey interaction involving sea urchins and their predators. Our results suggest that under future Ocean Acidification scenarios adult sea urchins defence strategies, such as spine length, test robustness and oral plate thickness, could be compromised together with their survival chance to natural predators. Sea urchins represent the critical linkage between top-down and bottom-up processes along Mediterranean rocky reefs, and the cumulative impacts of global and local stressors could lead to a decline producing cascading effects on benthic ecosystems.

Characterizing biogeochemical fluctuations in a world of extremes: A synthesis for temperate intertidal habitats in the face of global change

Coastal and intertidal habitats are at the forefront of anthropogenic influence and environmental change. The species occupying these habitats are adapted to a world of extremes, which may render them robust to the changing climate or more vulnerable if they are at their physiological limits. We characterized the diurnal, seasonal and interannual patterns of flux in biogeochemistry across an intertidal gradient on a temperate sandstone platform in eastern Australia over 6 years (2009-2015) and present a synthesis of our current understanding of this habitat in context with global change. We used rock pools as natural mesocosms to determine biogeochemistry dynamics and patterns of eco-stress experienced by resident biota. In situ measurements and discrete water samples were collected night and day during neap low tide events to capture diurnal biogeochemistry cycles. Calculation of pH_T using total alkalinity (TA) and dissolved inorganic carbon (DIC) revealed that the mid-intertidal habitat exhibited the greatest flux over the years (pH_T 7.52-8.87), and over a single tidal cycle (1.11 pH_T units), while the low-intertidal (pH_T 7.82-8.30) and subtidal (pH_T 7.87-8.30) were less variable. Temperature flux was also greatest in the mid-intertidal (8.0-34.5°C) and over a single tidal event (14°C range), as typical of temperate rocky shores. Mean TA and DIC increased at night and decreased during the day, with the most extreme conditions measured in the mid-intertidal owing to prolonged emersion periods. Temporal sampling revealed that net ecosystem calcification and production were highest during the day and lowest at night, particularly in the mid-intertidal. Characterization of biogeochemical fluctuations in a world of extremes demonstrates the variable conditions that intertidal biota routinely experience and highlight potential microhabitat-specific vulnerabilities and climate change refugia.

Ocean acidification affects microbial community and invertebrate settlement on biofilms

Increased atmospheric CO₂ is driving ocean acidification (OA), and potential changes in marine ecosystems. Research shows that both planktonic and benthic communities are affected, but how these changes are linked remains unresolved. Here we show experimentally that decreasing seawater pH (from pH 8.1 to 7.8 and 7.4) leads to reduced biofilm formation and lower primary producer biomass within biofilms. These changes occurred concurrently with a re-arrangement of the biofilm microbial communities. Changes suggest a potential shift from autotrophic to heterotrophic dominated biofilms in response to reduced pH. In a complimentary experiment, biofilms reared under reduced pH resulted in altered larval settlement for a model species (Galeolaria hystrix). These findings show that there is a potential cascade of impacts arising from OA effects on biofilms that may drive important community shifts through altered settlement patterns of benthic species.

Ocean warming and acidification pose synergistic limits to the thermal niche of an economically important echinoderm

To make robust projectios of the impacts of climate change, it is critical to understand how abiotic factors may interact to constrain the distribution and productivity of marine flora and fauna. We evaluated the effects of projected end of the century ocean acidification (OA) and warming (OW) on the thermal tolerance of an important living marine resource, the sea urchin Loxechinus albus, a benthic shallow water coastal herbivore inhabiting part of the Pacific coast of South America. After exposing young juveniles for a 1-month period to contrasting pCO₂ (~500 and 1400 μatm) and temperature (~15 °C and 20 °C) levels, critical thermal maximum (CTmax) and minimum (CTmin) as well as thermal tolerance polygons were assessed based on self-righting success as an end point. Transcription of heat shock protein 70 (HSP70), a chaperone protecting cellular proteins from environmental stress, was also measured. Exposure to elevated pCO₂ significantly reduced thermal tolerance by increasing CTmin at both experimental temperatures and decreasing CTmax at 20 °C. There was also a strong synergistic effect of OA × OW on HSP70 transcription levels which were 75 times higher than in control conditions. If this species is unable to adapt to elevated pCO₂ in the future, the reduction in thermal tolerance and HSP response suggests that near-future warming and OA will disrupt their performance and reduce their distribution with ecological and economic consequences. Given the wider latitudinal range (6 to 56°S) and environmental tolerance of L. albus compared to other members of this region's benthic invertebrate community, OW and OA may cause substantial changes to the coastal fauna along this geographical range.

The impact of environmental acidification on the microstructure and mechanical integrity of marine invertebrate skeletons

Ocean acidification (OA), from seawater uptake of anthropogenic CO_2, has a suite of negative effects on the ability of marine invertebrates to produce and maintain their skeletons. Increased organism pCO₂ causes hypercapnia, an energetically costly physiological stress. OA alters seawater carbonate chemistry, limiting the carbonate available to form the calcium carbonate (CaCO₃) minerals used to build skeletons. The reduced saturation state of CaCO₃ also causes corrosion of CaCO₃ structures. Global change is also accelerating coastal acidification driven by land-run off (e.g. acid soil leachates, tannic acid). Building and maintaining marine biomaterials in the face of changing climate will depend on the balance between calcification and dissolution. Overall, in response to environmental acidification, many calcifiers produce less biomineral and so have smaller body size. Studies of skeleton development in echinoderms and molluscs across life stages show the stunting effect of OA. For corals, linear extension may be maintained, but at the expense of less dense biomineral. Conventional metrics used to quantify growth and calcification need to be augmented by characterisation of the changes to biomineral structure and mechanical integrity caused by environmental acidification. Scanning electron microscopy and microcomputed tomography of corals, tube worms and sea urchins exposed to experimental (laboratory) and natural (vents, coastal run off) acidification show a less dense biomineral with greater porosity and a larger void space. For bivalves, CaCO₃ crystal deposition is more chaotic in response to both ocean and coastal acidification. Biomechanics tests reveal that these changes result in weaker, more fragile skeletons, compromising their vital protective roles. Vulnerabilities differ among taxa and depend on acidification level. Climate warming has the potential to ameliorate some of the negative effects of acidification but may also make matters worse. The integrative morphology-ecomechanics approach is key to understanding how marine biominerals will perform in the face of changing climate.

Building global change resilience: Concrete has the potential to ameliorate the negative effects of climate-driven ocean change on a newly-settled calcifying invertebrate

Global climate change is driving sea level rise and increasingly frequent storm events, which are negatively impacting rapidly-growing coastal communities. To mitigate these impacts, coastal infrastructure must be further protected by upgrading hard defences. We propose that incorporating pH-buffering materials into these upgrades could safeguard marine organisms from the adverse effects of ocean acidification and ocean warming during the vulnerable transition from planktonic larvae to benthic juveniles. To test this, we examined the effects of ocean warming (24 or 27 °C), ocean acidification (pH 8.1, 7.9, 7.7), and substratum (concrete, greywacke, granite) in all combinations on the settlement success of an ecologically and commercially important sea urchin, Tripneustes gratilla. Low pH (7.9, 7.7) generally reduced the quantity and size of juveniles four weeks post-settlement, although this was partially ameliorated by increased temperature (24 vs. 27 °C). In the warmed and acidified treatments, settlement rates were lower on concrete than granite or greywacke, but two weeks post-settlement, juveniles on concrete were larger, and had longer spines and higher survival rates than on greywacke or granite, respectively. The benefits provided by concrete to newly-settled juveniles may be related to alkali chemicals leaching from concrete buffering low pH conditions in surrounding seawater and/or increased availability of bicarbonate in the boundary layers around its surface. Our results highlight the potential for pH-buffering materials to assist marine organisms in coping with the effects of changing ocean conditions, but further research is required to understand the generality and mechanism(s) driving the beneficial effects of concrete and to test pH-buffering materials in the field.

Does exposure to reduced pH and diclofenac induce oxidative stress in marine bivalves? A comparative study with the mussel Mytilus galloprovincialis and the clam Ruditapes philippinarum

CO₂-driven acidification and emerging contaminants, such as pharmaceuticals, pose new threats for the maintenance of natural populations of marine organisms by interfering with their normal biochemical pathways and defences. The combined effects of seawater acidification, as predicted in climate change scenarios, and an emerging contaminant (the non-steroidal anti-inflammatory drug, NSAID, diclofenac) on oxidative stress-related parameters were investigated in the Mediterranean mussel Mytilus galloprovincialis and the Manila clam Ruditapes philippinarum. A flow-through system was used to carry out a three-week exposure experiment with the bivalves. First, the animals were exposed to only three pH values for 7 days. The pH was manipulated by dissolving CO₂ in the seawater to obtain two reduced pH treatments (pH -0.4 units and pH -0.7 units), which were compared with seawater at the natural pH level (8.1). Thereafter, the bivalves were concomitantly exposed to the three experimental pH values and environmentally relevant concentrations of diclofenac (0.00, 0.05 and 0.50 μg/L) for an additional 14 days. The activities of superoxide dismutase, catalase and cyclooxygenase, and lipid peroxidation and DNA strand-break formation were measured in both the gills and digestive gland after 7, 14 and 21 days of exposure to each experimental condition. The results show that the biochemical parameters measured in both the mussels and clams were more influenced by the reduced pH than by the contaminant or the pH*contaminant interaction, although the biomarker variation patterns differed depending on the species and tissues analysed. Generally, due to increases in its antioxidant defence, M. galloprovincialis was more resistant than R. philippinarum to both diclofenac exposure and reduced pH. Conversely, reduced pH induced a significant decrease in COX activity in both the gills and digestive gland of clams, possibly resulting in the increased DNA damage observed in the digestive gland tissue.

Effects of natural current pH variability on the sea urchin Paracentrotus lividus larvae development and settlement

One of the most important environmental factors controlling the distribution, physiology, morphology and behaviour of marine invertebrates is ocean pH. In the last decade, the effects of decreasing ocean pH as a result of climate change processes (i.e. ocean acidification) on marine organisms have been target of much research. However, the effects of natural pH variability in the species' niche have been largely neglected. Marine coastal habitats are characterized by a high environmental variability and, in some cases, organisms are already coping with pH values predicted by the end of the century. It is thought that because of adaptation or acclimation to natural environmental variability, intertidal species may have some resilience to future changes. In this study, we explored the sensitivities of the sea urchin Paracentrotus lividus during its larvae development and settlement undergoing two different daily pH frequencies (12 h fluctuation from 7.7 to 8.1 units of pH, and constant pH treatment of 8.1 units of pH) that have been currently recorded in the sampling region (Canary Islands). Results showed that, despite larvae development was slightly enhanced by moderated fluctuating pH regimes, P. lividus larva was able to develop normally in both, fluctuating and constant, pH environments. Results of the settlement experiment showed very clear patterns since postlarvae settlement was only successful when a covering of algae was added, regardless of the pH fluctuation applied.

Robustness of larval development of intertidal sea urchin species to simulated ocean warming and acidification

Ocean warming and acidification are the two most significant side effects of carbone dioxide emissions in the world's oceans. By changing water, temperature and pH are the main environmental factors controlling the distribution, physiology, morphology and behaviour of marine invertebrates. This study evaluated the combined effects of predicted high temperature levels, and predicted low pH values, on fertilization and early development stages of the sea urchins Arbacia lixula, Paracentrotus lividus, Sphaerechinus granularis and Diadema africanum. Twelve treatments, combining different temperatures (19, 21, 23 and 25 °C) and pH values (8.1, 7.7 and 7.4 units), were tested in laboratory experiments. All of the tested temperatures and pH values were within the open coast seawater range expected within the next century. We examined fertilization rate, cleavage rate, 3-day larvae survival, and development of the different sea urchin species at set time intervals after insemination. Our results highlight the susceptibility of subtidal species to environmental changes, and the robustness of intertidal species to ocean warming and acidification.

Transgenerational effects of ocean warming on the sea urchin Strongylocentrotus intermedius

Transgenerational effects, which involve both selection and plasticity, are important for the evolutionary adaptation of echinoderms in the changing ocean. Here, we investigated the effects of breeding design and water temperature for offspring on fertilization, hatchability, larval survival, size, abnormality and metamorphosis of the sea urchin Strongylocentrotus intermedius, whose dams and sires were exposed to long-term (~15 months) elevated temperature (~3°C above ambient) or ambient temperature. There was no transgenerational effect on fertilization and metamorphosis of S. intermedius, while negative transgenerational effects were found in hatchability and most traits of larval size. Dam and sire effects were highly trait and developmental stage dependent. Interestingly, we found S. intermedius probably cannot achieve transgenerational acclimation to long-term elevated temperature for survival provided their offspring were exposed to an elevated temperature. The present study enriches our understanding of transgenerational effects of ocean warming on sea urchins.

Ocean acidification alters zooplankton communities and increases top-down pressure of a cubozoan predator

The composition of local ecological communities is determined by the members of the regional community that are able to survive the abiotic and biotic conditions of a local ecosystem. Anthropogenic activities since the industrial revolution have increased atmospheric CO₂ concentrations, which have in turn decreased ocean pH and altered carbonate ion concentrations: so called ocean acidification (OA). Single-species experiments have shown how OA can dramatically affect zooplankton development, physiology and skeletal mineralization status, potentially reducing their defensive function and altering their predatory and antipredatory behaviors. This means that increased OA may indirectly alter the biotic conditions by modifying trophic interactions. We investigated how OA affects the impact of a cubozoan predator on their zooplankton prey, predominantly Copepoda, Pleocyemata, Dendrobranchiata, and Amphipoda. Experimental conditions were set at either current (pCO₂ 370 μatm) or end-of-the-century OA (pCO₂ 1,100 μatm) scenarios, crossed in an orthogonal experimental design with the presence/absence of the cubozoan predator Carybdea rastoni. The combined effects of exposure to OA and predation by C. rastoni caused greater shifts in community structure, and greater reductions in the abundance of key taxa than would be predicted from combining the effect of each stressor in isolation. Specifically, we show that in the combined presence of OA and a cubozoan predator, populations of the most abundant member of the zooplankton community (calanoid copepods) were reduced 27% more than it would be predicted based on the effects of these stressors in isolation, suggesting that OA increases the susceptibility of plankton to predation. Our results indicate that the ecological consequences of OA may be greater than predicted from single-species experiments, and highlight the need to understand future marine global change from a community perspective.

Sea urchins in a high-CO2 world: the influence of acclimation on the immune response to ocean warming and acidification

Climate-induced ocean warming and acidification may render marine organisms more vulnerable to infectious diseases. We investigated the effects of warming and acidification on the immune response of the sea urchin Heliocidaris erythrogramma Sea urchins were gradually introduced to four combinations of temperature and pHNIST (17°C/pH 8.15, 17°C/pH 7.6, 23°C/pH 8.15 and 23°C/pH 7.6) and then held in temperature-pH treatments for 1, 15 or 30 days to determine if the immune response would adjust to stressors over time. Coelomocyte concentration and type, phagocytic capacity and bactericidal activity were measured on day 1, 15 and 30 with different sea urchins used each time. At each time point, the coelomic fluid of individuals exposed to increased temperature and acidification had the lowest coelomocyte concentrations, exhibited lower phagocytic capacities and was least effective at inhibiting bacterial growth of the pathogen Vibrio anguillarum Over time, increased temperature alleviated the negative effects of acidification on phagocytic activity. Our results demonstrate the importance of incorporating acclimation time to multiple stressors when assessing potential responses to future ocean conditions and indicate that the immune response of H. erythrogramma may be compromised under near-future ocean warming and acidification.

Ocean Acidification Reduces Spine Mechanical Strength in Euechinoid but Not in Cidaroid Sea Urchins

Echinoderms are considered particularly sensitive to ocean acidification (OA) as their skeleton is made of high-magnesium calcite, one of the most soluble forms of calcium carbonate. Recent studies have investigated effects of OA on the skeleton of "classical" sea urchins (euechinoids), but the impact of etching on skeleton mechanical properties is almost unknown. Furthermore, the integrity of the skeleton of cidaroids has never been assessed, although their extracellular fluid is under-saturated with respect to their skeleton, and the skeleton of their primary spines is in direct contact with seawater. In this study, we compared the dissolution of test plates and spines as well as the spine mechanical properties (two-points bending tests) in a cidaroid (Eucidaris tribuloides) and a euechinoid (Tripneustes ventricosus) submitted to a 5 week acidification experiment (pH_T of 8.1, 7.7, and 7.4). Test plates of both species were not affected by dissolution. The spines of E. tribuloides showed no mechanical effects at pH_SW-T 7.4 despite having traces of corrosion on secondary spines. On the contrary, spines of the T. ventricosus were significantly etched at both pH_SW-T 7.7 and 7.4 and their fracture force reduced by 16 to 35%, respectively. This increased brittleness is probably of little significance with regards to predation protection but has consequences in terms of energy allocation.

Effects of long-term elevated temperature on covering, sheltering and righting behaviors of the sea urchin Strongylocentrotus intermedius

Increases in ocean temperature due to climate change are predicted to change the behaviors of marine invertebrates. Altered behaviors of keystone ecosystem engineers such as echinoderms will have consequences for the fitness of individuals, which are expected to flow on to the local ecosystem. Relatively few studies have investigated the behavioral responses of echinoderms to long-term elevated temperature. We investigated the effects of exposure to long-term (∼31 weeks) elevated temperature (∼3 °C above the ambient water temperature) on covering, sheltering and righting behaviors of the sea urchin Strongylocentrotus intermedius. Long-term elevated temperature showed different effects on the three behaviors. It significantly decreased covering behavior, including both covering behavior reaction (time to first covering) and ability (number of covered sea urchins and number of shells used for covering). Conversely, exposure to long-term elevated temperature significantly increased sheltering behavior. Righting response in S. intermedius was not significantly different between temperature treatments. The results provide new information into behavioral responses of echinoderms to ocean warming.

Future aquafeeds may compromise reproductive fitness in a marine invertebrate

Aquaculture of higher trophic level species is increasingly dependent on the use of terrestrial oil products. The input of terrestrially derived n-6 polyunsaturated fatty acids (PUFA) into marine environments has subsequently increased, with unknown consequences for recipient species. We exposed a sea urchin, Heliocidaris erythrogramma to three experimental diets for 78 days: a high n-3 PUFA marine imitation treatment, a high n-6 PUFA "future aquafeed" treatment and an intermediate "current aquafeed" treatment. Female urchins fed the high n-6 PUFA diet produced larvae with lower survival rates than all other treatments. Males fed the high n-6 PUFA diet produced no viable sperm. Fatty acid composition in reproductive material revealed comprehensive biosynthetic and dietary sparing capabilities in H. erythrogramma. Despite this, the ratio of n-6 PUFA to n-3 PUFA in reproductive tissue increased significantly with diet. We suggest alterations to this ratio is the likely mechanism of negative impact on larval development.

Ocean Acidification and Increased Temperature Have Both Positive and Negative Effects on Early Ontogenetic Traits of a Rocky Shore Keystone Predator Species

The combined effect of ocean acidification and warming is expected to have significant effects on several traits of marine organisms. The gastropod Concholepas concholepas is a rocky shore keystone predator characteristic of the south-eastern Pacific coast of South America and an important natural resource exploited by small-scale artisanal fishermen along the coast of Chile and Peru. In this study, we used small juveniles of C. concholepas collected from the rocky intertidal habitats of southern Chile (39°S) to evaluate under laboratory conditions the potential consequences of projected near-future levels of ocean acidification and warming for important early ontogenetic traits. The individuals were exposed long-term (5.8 months) to contrasting pCO₂ (ca. 500 and 1400 μatm) and temperature (15 and 19°C) levels. After this period we compared body growth traits, dislodgement resistance, predator-escape response, self-righting and metabolic rates. With respect to these traits there was no evidence of a synergistic interaction between pCO₂ and temperature. Shell growth was negatively affected by high pCO₂ levels only at 15°C. High pCO₂ levels also had a negative effect on the predator-escape response. Conversely, dislodgement resistance and self-righting were positively affected by high pCO₂ levels at both temperatures. High tenacity and fast self-righting would reduce predation risk in nature and might compensate for the negative effects of high pCO₂ levels on other important defensive traits such as shell size and escape behaviour. We conclude that climate change might produce in C. concholepas positive and negative effects in physiology and behaviour. In fact, some of the behavioural responses might be a consequence of physiological effects, such as changes in chemosensory capacity (e.g. predator-escape response) or secretion of adhesive mucous (e.g. dislodgement resistance). Moreover, we conclude that positive behavioural responses may assist in the adaptation to negative physiological impacts, and that this may also be the case for other benthic organisms.

Are global warming and ocean acidification conspiring against marine ectotherms? A meta-analysis of the respiratory effects of elevated temperature, high CO2 and their interaction

With the occurrence of global change, research aimed at estimating the performance of marine ectotherms in a warmer and acidified future has intensified. The concept of oxygen- and capacity-limited thermal tolerance, which is inspired by the Fry paradigm of a bell-shaped increase-optimum-decrease-type response of aerobic scope to increasing temperature, but also includes proposed negative and synergistic effects of elevated CO2 levels, has been suggested as a unifying framework. The objectives of this meta-analysis were to assess the following: (i) the generality of a bell-shaped relationship between absolute aerobic scope (AAS) and temperature; (ii) to what extent elevated CO2 affects resting oxygen uptake MO2rest and AAS; and (iii) whether there is an interaction between elevated temperature and CO2. The behavioural effects of CO2 are also briefly discussed. In 31 out of 73 data sets (both acutely exposed and acclimated), AAS increased and remained above 90% of the maximum, whereas a clear thermal optimum was observed in the remaining 42 data sets. Carbon dioxide caused a significant rise in MO2rest in only 18 out of 125 data sets, and a decrease in 25, whereas it caused a decrease in AAS in four out of 18 data sets and an increase in two. The analysis did not reveal clear evidence for an overall correlation with temperature, CO2 regime or duration of CO2 treatment. When CO2 had an effect, additive rather than synergistic interactions with temperature were most common and, interestingly, they even interacted antagonistically on MO2rest and AAS. The behavioural effects of CO2 could complicate experimental determination of respiratory performance. Overall, this meta-analysis reveals heterogeneity in the responses to elevated temperature and CO2 that is not in accordance with the idea of a single unifying principle and which cannot be ignored in attempts to model and predict the impacts of global warming and ocean acidification on marine ectotherms.

Biogenic acidification reduces sea urchin gonad growth and increases susceptibility of aquaculture to ocean acidification

Decreasing oceanic pH (ocean acidification) has emphasised the influence of carbonate chemistry on growth of calcifying marine organisms. However, calcifiers can also change carbonate chemistry of surrounding seawater through respiration and calcification, a potential limitation for aquaculture. This study examined how seawater exchange rate and stocking density of the sea urchin Tripneustes gratilla that were reproductively mature affected carbonate system parameters of their culture water, which in turn influenced growth, gonad production and gonad condition. Growth, relative spine length, gonad production and consumption rates were reduced by up to 67% by increased density (9-43 individuals.m(-2)) and reduced exchange rates (3.0-0.3 exchanges.hr(-1)), but survival and food conversion efficiency were unaffected. Analysis of the influence of seawater parameters indicated that reduced pH and calcite saturation state (ΩCa) were the primary factors limiting gonad production and growth. Uptake of bicarbonate and release of respiratory CO2 by T. gratilla changed the carbonate chemistry of surrounding water. Importantly total alkalinity (AT) was reduced, likely due to calcification by the urchins. Low AT limits the capacity of culture water to buffer against acidification. Direct management to counter biogenic acidification will be required to maintain productivity and reproductive output of marine calcifiers, especially as the ocean carbonate system is altered by climate driven ocean acidification.

Urchins in a high CO2 world: partitioned effects of body-size, ocean warming and acidification on metabolic rate

Body-size and temperature are the major factors explaining metabolic rate, and the additional factor of pH is a major driver at the biochemical level. These three factors have frequently been found to interact, complicating the formulation of broad models predicting metabolic rates and hence ecological functioning. In this first study of the effects of warming and ocean acidification, and their potential interaction, on metabolic rate across a broad body-size range (two-to-three orders of magnitude difference in body mass) we addressed the impact of climate change on the sea urchin Heliocidaris erythrogramma in context with climate projections for east Australia, an ocean warming hotspot. Urchins were gradually introduced to two temperatures (18 and 23 °C) and two pH (7.5 and 8.0), and maintained for two months. That a new physiological steady-state had been reached, otherwise know as acclimation, was validated through identical experimental trials separated by several weeks. The relationship between body-size, temperature and acidification on the metabolic rate of H. erythrogramma was strikingly stable. Both stressors caused increases in metabolic rate; 20% for temperature and 19% for pH. Combined effects were additive; a 44% increase in metabolism. Body-size had a highly stable relationship with metabolic rate regardless of temperature or pH. None of these diverse drivers of metabolism interacted or modulated the effects of the others, highlighting the partitioned nature of how each influences metabolic rate, and the importance of achieving a full acclimation state. Despite these increases in energetic demand there was very limited capacity for compensatory modulating of feeding rate; food consumption increased only in the very smallest specimens, and only in response to temperature, and not pH. Our data show that warming, acidification and body-size all substantially affect metabolism and are highly consistent and partitioned in their effects, and for H. erythrogramma near-future climate change will incur a substantial energetic cost.

Ocean warming ameliorates the negative effects of ocean acidification on Paracentrotus lividus larval development and settlement

Ocean warming and acidification both impact marine ecosystems. All organisms have a limited body temperature range, outside of which they become functionally constrained. Beyond the absolute extremes of this range, they cannot survive. It is hypothesized that some stressors can present effects that interact with other environmental variables, such as ocean acidification (OA) that have the potential to narrow the thermal range where marine species are functional. An organism's response to ocean acidification can therefore be highly dependent on thermal conditions. This study evaluated the combined effects of predicted ocean warming conditions and acidification, on survival, development, and settlement, of the sea urchin Paracentrotus lividus. Nine combined treatments of temperature (19.0, 20.5 and 22.5 °C) and pH (8.1, 7.7 and 7.4 units) were carried out. All of the conditions tested were either within the current natural ranges of seawater pH and temperature or are within the ranges that have been predicted for the end of the century, in the sampling region (Canary Islands). Our results indicated that the negative effects of low pH on P. lividus larval development and settlement will be mitigated by a rise in seawater temperature, up to a thermotolerance threshold. Larval development and settlement performance of the sea urchin P. lividus was enhanced by a slight increase in temperature, even under lowered pH conditions. However, the species did show negative responses to the levels of ocean warming and acidification that have been predicted for the turn of the century.

Long-term mesocosms study of the effects of ocean acidification on growth and physiology of the sea urchin Echinometra mathaei

Recent research on the impact of ocean acidification (OA) has highlighted that it is important to conduct long-term experiments including ecosystem interactions in order to better predict the possible effects of elevated pCO2. The goal of the present study was to assess the long-term impact of OA on a suite of physiological parameters of the sea urchin Echinometra mathaei in more realistic food conditions. A long-term experiment was conducted in mesocosms provided with an artificial reef in which the urchins principally fed on algae attached to the reef calcareous substrate. Contrasted pH conditions (pH 7.7 vs control) were established gradually over six months and then maintained for seven more months. Acid-base parameters of the coelomic fluid, growth and respiration rate were monitored throughout the experiment. Results indicate that E. mathaei should be able to regulate its extracellular pH at long-term, through bicarbonate compensation. We suggest that, within sea urchins species, the ability to accumulate bicarbonates is related to their phylogeny but also on the quantity and quality of available food. Growth, respiration rate and mechanical properties of the test were not affected. This ability to resist OA levels expected for 2100 at long-term could determine the future of coral reefs, particularly reefs where E. mathaei is the major bioeroder.

Early development of congeneric sea urchins (Heliocidaris) with contrasting life history modes in a warming and high CO2 ocean

The impacts of ocean change stressors - warming and acidification - on marine invertebrate development have emerged as a significant impact of global change. We investigated the response of early development to the larval stage in sympatric, congeneric sea urchins, Heliocidaris tuberculata and Heliocidaris erythrogramma with contrasting modes of development to ocean warming and acidification. Effects of these stressors were assessed by quantifying the percentage of normal development during the first 24 h post fertilization, in cross-factorial experiments that included three temperature treatments (control: 20 °C; +4: 24 °C; +6: 26 °C) and four pHNIST levels (control: 8.2; -0.4: 7.8; -0.6: 7.6; -0.8: 0.4). The experimental treatments were designed in context with present day and near-future (∼2100) conditions for the southeast Australia global warming hotspot. Temperature was the most important factor affecting development of both species causing faster progression through developmental stages as well as a decrease in the percentage of normal development. H. erythrogramma embryos were less tolerant of increased temperature than those of H. tuberculata. Acidification impaired development to the larval stage in H. tuberculata, but this was not the case for H. erythrogramma. Thus, outcomes for the planktonic life phase of the two Heliocidaris species in response to ocean warming and acidification will differ. As shown for these species, single-stressor temperature or acidification studies can be misleading with respect to determining species' vulnerability and responses to global change.

Warming influences Mg2+ content, while warming and acidification influence calcification and test strength of a sea urchin

We examined the long-term effects of near-future changes in temperature and acidification on skeletal mineralogy, thickness, and strength in the sea urchin Tripneustes gratilla reared in all combinations of three pH (pH 8.1, 7.8, 7.6) and three temperatures (22 °C, 25 °C, 28 °C) from the early juvenile to adult, over 146 days. As the high-magnesium calcite of the echinoderm skeleton is a biomineral form highly sensitive to acidification, and influenced by temperature, we documented the MgCO3 content of the spines, test plates, and teeth. The percentage of MgCO3 varied systematically, with more Mg2+ in the test and spines. The percentage of MgCO3 in the test and teeth, but not the spines increased with temperature. Acidification did not change the percentage MgCO3. Test thickness increased with warming and decreased at pH 7.6, with no interaction between these factors. In crushing tests live urchins mostly ruptured at sutures between the plates. The force required to crush a live urchin was reduced in animals reared in low pH conditions but increased in those reared in warm conditions, a result driven by differences in urchin size. It appears that the interactive effects of warming and acidification on the Mg2+ content and protective function of the sea urchin skeleton will play out in a complex way as global climatic change unfolds.

The skeleton of postmetamorphic echinoderms in a changing world

Available evidence on the impact of acidification and its interaction with warming on the skeleton of postmetamorphic (juvenile and adult) echinoderms is reviewed. Data are available on sea urchins, starfish, and brittle stars in 33 studies. Skeleton growth of juveniles of all sea urchin species studied so far is affected from pH 7.8 to 7.6 in seawater, values that are expected to be reached during the 21st century. Growth in adult sea urchins (six species studied) is apparently only marginally affected at seawater pH relevant to this century. The interacting effect of temperature differed according to studies. Juvenile starfish as well as adults seem to be either not impacted or even boosted by acidification. Brittle stars show moderate effects at pH below or equal to 7.4. Dissolution of the body wall skeleton is unlikely to be a major threat to sea urchins. Spines, however, due to their exposed position, are more prone to this threat, but their regeneration abilities can probably ensure their maintenance, although this could have an energetic cost and induce changes in resource allocation. No information is available on skeleton dissolution in starfish, and the situation in brittle stars needs further assessment. Very preliminary evidence indicates that mechanical properties in sea urchins could be affected. So, although the impact of ocean acidification on the skeleton of echinoderms has been considered as a major threat from the first studies, we need a better understanding of the induced changes, in particular the functional consequences of growth modifications and dissolution related to mechanical properties. It is suggested to focus studies on these aspects.

Corallina and Ellisolandia (Corallinales, Rhodophyta) photophysiology over daylight tidal emersion: interactions with irradiance, temperature and carbonate chemistry

The photophysiology of three geniculate coralline algal species (Corallina officinalis, C. caespitosa and Ellisolandia elongata) was determined in intertidal rock pools in the south-west UK at Combe Martin (51°12'31N 4°2'19W) and Heybrook Bay (50°31'66N 4°11'41W), at the start, middle and end of summer (September 1 and 2) and winter (February 9 and 10) daylight tidal emersion periods, in relation to prevailing irradiance, temperature and carbonate chemistry conditions. Algal photophysiology was assessed from rapid light curves performed using pulse amplitude modulation fluorometry. Corallina and Ellisolandia experienced significant fluctuations in irradiance, temperature and carbonate chemistry over seasonal and tidal cycles. Rock pool carbonate chemistry was predictable (R² = 0.82, P < 0.0001) by photodose (summed irradiance) plus water temperature, but not significantly related to photophysiology. In contrast, Corallina and Ellisolandia relative maximum electron transfer rate showed a significant negative relationship (R² = 0.65, P < 0.0001) with irradiance plus water temperature. At a seasonal resolution, photoacclimation to maximize both light harvesting during winter months and photoprotection during summer months was observed for all species. Dynamic photoinhibition was apparent over both summer and winter tidal emersion, in relation to irradiance fluctuations. More effective photoinhibition was apparent during summer months, with greater sensitivity to irradiance and slower recovery in F_v/F_m, observed during winter. With sustained high irradiance over tidal emersion, the establishment of high pH/low inorganic carbon conditions may impact photochemistry. This study represents the first assessment of C. officinalis, C. caespitosa and E. elongata photophysiology underpinned by clear species concepts and highlights their ability to adapt to the dramatically fluctuating conditions experienced in intertidal rock pools.

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.