Impact of near-future ocean acidification on echinoderms

Long-term study of the combined effects of ocean acidification and warming on the mottled brittle star, Ophionereis fasciata

The global ocean is rapidly changing, posing a substantial threat to the viability of marine populations due to the co-occurrence of multiple drivers, such as ocean warming (OW) and ocean acidification (OA). To persist, marine species must undergo some combination of acclimation and adaptation in response to these changes. Understanding such responses is essential to measure and project the magnitude and direction of current and future vulnerabilities in marine ecosystems. Echinoderms have been recognised as a model in studies of OW-OA effects on marine biota. However, despite their global diversity, vulnerability and ecological importance in most marine habitats, brittle stars (ophiuroids) are poorly studied. A long-term mesocosm experiment was conducted on adult mottled brittle star (Ophionereis fasciata) as a case study to investigate the physiological response and trade-offs of marine organisms to ocean acidification, ocean warming and the combined effect of these two drivers. Long-term exposure of O. fasciata to high temperature and low pH affected survival, respiration and regeneration rates, growth rate, calcification/dissolution and righting response. Higher temperatures increased stress and respiration, and decreased regeneration and growth rates as well as survival. Conversely, changes in pH had more subtle or no effect, affecting only respiration and calcification. Our results indicate that exposure to a combination of high temperature and low pH produces complex responses for respiration, righting response and calcification. We address the knowledge gap of the impact of a changing ocean on ophiuroids in the context of echinoderm studies, proposing this class as an ideal alternative echinoderm for future research.

Impact of tropical cyclone Biparjoy on oceanic parameters in the Arabian Sea

Climate change is expected to intensify tropical cyclones (TCs), requiring a deeper understanding of their ecosystem impacts. This study investigated TC Biparjoy impact on parameters from June 6 to 19, 2023, using satellite and vertical profiles. Initially, Chlorophyll-a levels remained steady but surged above 4 mg/m3 after the high-intensity phase, indicating increased phytoplankton biomass. Sea surface temperature (SST) initially exceeded 32 °C, favoring cyclone intensification, but dropped below 26 °C post-high-intensity phase due to mixing and upwelling of cooler waters. The SST gradient exceeded 0.15 °C/km post-cyclone. Elevated sea surface height around 0.5 m offshore and over 1 m along the coast was recorded. Wind stress values exceeding 0.4 N/m3 were observed during the high-intensity phase. Vertical profile showed uplifted low-temperature, nutrient-rich waters, enhancing phytoplankton productivity, supported by increased nitrate (>10 mmol/m3) and phosphate (>1.2 mmol/m3) levels. Additionally, slight increase in DIC, and pH during the cyclone period suggested changes in biogeochemical processes.

Are Microfibers a Threat to Marine Invertebrates? A Sea Urchin Toxicity Assessment

The rise of "fast fashion" has driven up the production of low-cost, short-lived clothing, significantly increasing global textile fiber production and, consequently, exacerbating environmental pollution. This study investigated the ecotoxicological effects of different types of anthropogenic microfibers-cotton, polyester, and mixed fibers (50% cotton: 50% polyester)-on marine organisms, specifically sea urchin embryos. All tested fibers exhibited toxicity, with cotton fibers causing notable effects on embryonic development even at environmentally relevant concentrations. The research also simulated a scenario where microfibers were immersed in seawater for 30 days to assess changes in toxicity over time. The results showed that the toxicity of microfibers increased with both concentration and exposure duration, with polyester being the most toxic among the fibers tested. Although synthetic fibers have been the primary focus of previous research, this study highlights that natural fibers like cotton, which are often overlooked, can also be toxic due to the presence of harmful additives. These natural fibers, despite decomposing faster than synthetic ones, can persist in aquatic environments for extended periods. The findings underline the critical need for further research on both natural and synthetic microfibers to understand their environmental impact and potential threats to marine ecosystems and sea urchin populations.

Drivers of biological response to fluctuating seawater ph conditions in sea urchin echinus esculentus larvae

A large body of evidence is documenting the impact of reduced pH on marine species and ecosystems. This information is used to infer the present and future impacts of ocean acidification. However, a vast majority of the studies were performed using constant pH and the high level of pH variability experienced by marine organisms on the coastal zone was often overlooked. Recent studies highlight the key role of this variability in driving biological response to pH as well as species sensitivity to ocean acidification. For example, it was hypothesized that because of local adaptation, the extreme of the present range of pH variability is a good predictor for local biological thresholds. Using a complex experimental design, we investigated what part of the pH variability is driving the biological response of the sea urchin Echinus esculentus larvae. Comparing stable (pH 8.13, 7.82, 7.53) and fluctuating treatments (12 h at pH 8.13 and 12 h at pH 7.53) following natural or inverted diurnal cycles, we were able to show that (i) under constant conditions, low pH deviating from the present range of natural variability had a negative effect on larval growth rate and calcification; (ii) under fluctuating conditions, a desynchronization of the pH variation with the photoperiod led to decreased larval growth rate and calcification; (iii) overall, larval fitness (survival, growth and calcification) was higher under fluctuating conditions as compared to constant. While these data do not support the hypothesis that the minimum pH is the main driver of the biological response, they provide evidence of adaptation to variability in a coastal species with associated a cost of plasticity but not a cost of canalization.

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.

De Novo Assembly of the Genome of the Sea Urchin Paracentrotus lividus (Lamarck 1816)

The Mediterranean purple sea urchin Paracentrotus lividus (Lamarck 1816) is a remarkable model system for molecular, evolutionary and cell biology studies, particularly in the field of developmental biology. We sequenced the genome, performed a de novo assembly, and analysed the assembly content. The genome of P. lividus was sequenced using Illumina NextSeq 500 System (Illumina) in a 2 × 150 paired-end format. More than 30,000 open reading frames (ORFs), (more than 8000 are unique), were identified and analysed to provide molecular tools accessible for the scientific community. In particular, several genes involved in complex innate immune responses, oxidative metabolism, signal transduction, and kinome, as well as genes regulating the membrane receptors, were identified in the P. lividus genome. In this way, the employment of the Mediterranean sea urchin for investigations and comparative analyses was empowered, leading to the explanation of cis-regulatory networks and their evolution in a key developmental model occupying an important evolutionary position with respect to vertebrates and humans.

Coastal aquaculture in Bangladesh: Sundarbans's role against climate change

The Sundarbans, a natural shield on earth, is one and only place that has many noteworthy environmental and geographical values with breathtaking natural beauties. Near the Sundarbans area, proliferation of aquaculture in this delta contributes appreciably to the national economy. Although aquaculture has become a means of daily livelihood, this sector is nevertheless threatened by a complex of climate change impacts. Cyclones, rising temperatures, rising sea levels, coastal flooding, and erosion make coastal farming difficult. As a panacea, the Sundarbans can play a critical role in preserving coastal aquaculture. As noticed, forests have high potential to recover from unusual consequences of climate change. Practicing safe aquaculture should be opted to refrain from endangering the Sundarbans. This review addressed various climate change impacts on coastal farming and identified the capabilities of the Sundarbans to protect coastal aquaculture from calamitous impacts. Findings show clues for researchers to analyze problems, consequences, and mitigations.

The Reproductive Capacities of the Calanoid Copepods Parvocalanus crassirostis and Acartia pacifica under Different pH and Temperature Conditions

The increasing atmospheric CO₂ concentrations and warming of marine waters have encouraged experiments on multi-stressor interactions in marine organisms. We conducted a multigenerational experiment to assess reproductive capacities regarding egg production in calanoid copepods Parvocalanus crassirostis and Acartia pacifica under different pH and temperature conditions. The experimental set-up allowed assessing the tandem effect of warming and acidification on the number of eggs produced by healthy copepod pairs under two pH conditions of 8.20 and 7.50 (hard selection) as well as with a gradual reduction of 0.05 pH units at each generation (soft selection). The results are quite interesting, with very diverse performance across temperatures. The number of eggs produced under hard selection was higher at pH 8.20 compared to pH 7.50 for both species, with the maximum number of eggs produced at 24-28 °C, whereas under soft selection, there was no significant difference in the egg production rate at 24-28 °C across generations and there was an improvement in the number of eggs produced at 8-16 °C. The results provide evidence that in a future ocean scenario of lower pH and higher temperature, the two species, and possibly the copepod population at large, might not decrease. Copepod populations might be resilient, and the transcriptomic evidence of adaptation to increased temperature and lower pH is a ray of hope. We believe further studies are needed to provide more robust datasets to underpin the hypothesis of adaptation to climate change.

Ocean acidification increases inorganic carbon over organic carbon in shrimp's exoskeleton

Ocean acidification (OA) may either increase or have a neutral effect on the calcification in shrimp's exoskeleton. However, investigations on changes in the carbon composition of shrimp's exoskeletons under OA are lacking. We exposed juvenile Pacific white shrimps to target pHs of 8.0, 7.9, and 7.6 for 100 days to evaluate changes in carapace thickness, total carbon (TC), particulate organic carbon (POC), particulate inorganic carbon (PIC), calcium, and magnesium concentrations in their exoskeletons. The PIC: POC ratio of shrimp in pH 7.6 treatment was significantly higher by 175 % as compared to pH 8.0 treatment. Thickness and Ca% in pH 7.6 treatment were significantly higher as compared to pH 8.0 treatment (90 % and 65 %, respectively). This is the first direct evidence of an increased PIC: POC ratio in shrimp exoskeletons under OA. In the future, such changes in carbon composition may affect the shrimp population, ecosystem functions, and regional carbon cycle.

Modulation of stress factors for cryopreservation of Paracentrotus lividus (Lamarck 1816) larvae

In the present work we modulated two stress factors salinity and temperature, whose ranges have been previously determined by bioassays using six pre-treatments (18 °C-29.5‰; 18 °C-35‰; 18 °C-39‰ and 20 °C-29.5‰; 20 °C-35‰; 20 °C-39‰), in order to obtain a successful cryopreservation protocol for pluteus larvae of the sea urchin P. lividus (Lamarck 1816). Toxicity tests were performed with different cryoprotectants in a range of 0.5-3 M. Best results pointed out to METH and Me₂SO as those more suitable for cryopreservation. First an exploratory cryopreservation experiment with Me₂SO supplemented with 0.04 M trehalose (TRE) was tested following the protocol for cryopreservation of embryos (8-h blastula) of Bellas and Paredes, 2011, which did not give satisfactory results. A cryopreservation experiment was performed with both cryoprotectants supplemented with 0.04 M trehalose on 4-arm pluteus larvae (48 h-old) developed in these pre-treatment conditions, followed by a simpler and shorter protocol with a cooling rate of 1 °C/min to -35 °C, achieving for the first time the successful cryopreservation of P. lividus larvae. When larvae were incubated in low salinity or low temperature pre-treatments, they showed delayed larval development and abnormalities. In contrast, pretreatments with high temperature and salinity showed good results. Dimethyl sulfoxide with trehalose proved to be the only effective cryoprotectant for successful cryopreservation of P. lividus larvae. The success of dimethyl sulfoxide is consistent with that described for other cases in previous literature, where dimethyl sulfoxide, although not the least toxic compound, gave the best cryopreservation result.

A review on recent advances in the electrochemical reduction of CO2 to CO with nano-electrocatalysts

The electrochemical reduction (ECR) of CO2 is a powerful strategy to reduce the world's carbon footprint by converting CO2 to useful products such as CH3OH and CO. Recent techno-economic analysis has found that for the electro-conversion of CO2 to be adapted for practical use, the main products formed from this reaction need to be low-order, such as CO. This review summarizes recent progress in the ECR of CO2 to CO on nano-electrocatalysts (noble, non-noble metals and carbon nanomaterials) and provides the limitations and challenges that each electrocatalyst faces. It discusses the mechanism behind the performance of the electrocatalysts and offers the potential future prospects of the ECR process.

Ocean Warming Amplifies the Effects of Ocean Acidification on Skeletal Mineralogy and Microstructure in the Asterinid Starfish Aquilonastra yairi

Ocean acidification and ocean warming compromise the capacity of calcifying marine organisms to generate and maintain their skeletons. While many marine calcifying organisms precipitate low-Mg calcite or aragonite, the skeleton of echinoderms consists of more soluble Mg-calcite. To assess the impact of exposure to elevated temperature and increased pCO2 on the skeleton of echinoderms, in particular the mineralogy and microstructure, the starfish Aquilonastra yairi (Echinodermata: Asteroidea) was exposed for 90 days to simulated ocean warming (27 °C and 32 °C) and ocean acidification (455 µatm, 1052 µatm, 2066 µatm) conditions. The results indicate that temperature is the major factor controlling the skeletal Mg (Mg/Ca ratio and Mgnorm ratio), but not for skeletal Sr (Sr/Ca ratio and Srnorm ratio) and skeletal Ca (Canorm ratio) in A. yairi. Nevertheless, inter-individual variability in skeletal Sr and Ca ratios increased with higher temperature. Elevated pCO2 did not induce any statistically significant element alterations of the skeleton in all treatments over the incubation time, but increased pCO2 concentrations might possess an indirect effect on skeletal mineral ratio alteration. The influence of increased pCO2 was more relevant than that of increased temperature on skeletal microstructures. pCO2 as a sole stressor caused alterations on stereom structure and degradation on the skeletal structure of A. yairi, whereas temperature did not; however, skeletons exposed to elevated pCO2 and high temperature show a strongly altered skeleton structure compared to ambient temperature. These results indicate that ocean warming might exacerbate the skeletal maintaining mechanisms of the starfish in a high pCO2 environment and could potentially modify the morphology and functions of the starfish skeleton.

Responses of sea urchins (Strongylocentrotus intermedius) with different sexes to CO2-induced seawater acidification: Histology, physiology, and metabolomics

Responses of different sexes of farmed Strongylocentrotus intermedius to chronic CO₂-induced seawater acidification were investigated in 120-day lab-based experiments. Four experimental groups were set up as one control group and three seawater acidification groups. The results showed that 1) Specific growth rate and the numbers of mature gamete cells declined in a pH-dependent way in both sexes of adult S. intermedius. 2) There were differences in SDMs identified in females and males reared in acidified seawater reflecting sex-specific response variation in adult S. intermedius. 3) The number of altered metabolic pathways exhibited a linear increasing trend as seawater pH declined in both sexes of adult S. intermedius. Meanwhile seawater acidification might affect metabolic processes via changing the relative expression and activity of key enzymes controlling the corresponding metabolic pathways of adult S. intermedius.

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.

Comparing genetic markers’ efficiencies for discrimination between two commercially important holothuroids in the Mediterranean Sea, Holothuria polii and Holothuria sanctori

Sea cucumber (bêche-de-mer, Echinodermata: Holothuroidea) is one of the top internationally traded seafood varieties. Besides its direct nutritional benefits, it is continuously used in the traditional medicine in different areas and cultures in the world. This world-wide interest triggered various issues related to stocks´ declining and risks of species extinction. For these reasons, the current study was designed to provide molecular tools for accurate discrimination between two sea cucumber species that prevail the Mediterranean of these echinoderms in Egypt, that are Holothuria polii and H. sanctori. The power of three gene markers, i.e., 16S rDNA, 28S rDNA, and Histone H3 in achieving accurate DNA-based identification, as well as elucidating clear phylogenetic and genetic diversity differences between those two species was assessed. Among the three genes, 16S rDNA showed the highest potentials as genetic and phylogenetic species discrimination marker. Both 28S rDNA and H3 exhibited the least number of holothuroid reference sequences in the GenBank database. For genetic diversity within each species population, 16S rDNA exhibited the best potentials, followed by H3. 28S rDNA showed no genetic polymorphism at all. Moreover, the collective data of both H3 and 16S rDNA suggested a possible role of asexual reproduction behavior in H. sanctori in the reduction of genetic diversity, as a possible response to overfishing. Hence, the current research can recommend the simultaneous application of both 16S rDNA and H3 as accurate markers for genetic discrimination among H. polii, H. sanctori and other different holothuroid species.  

Near future ocean acidification modulates the physiological impact of fluoxetine at environmental concentration on larval urchins

Pharmaceuticals found in human wastes are emergent pollutants that are continuously released into aquatic systems. While exposure to pharmaceuticals alone could adversely impact aquatic organisms, few studies have considered the interactive effects of pharmaceuticals and the future environmental conditions, such as decreasing pH due to ocean acidification. Given the bioavailability of many pharmaceuticals is dependent on these physical conditions, we investigated the effect of environmentally-relevant concentrations of fluoxetine (10 and 100 ng L^-1) under ambient (pH 8.0) and reduced pH conditions (pH 7.7) on physiology, behavior, and DNA integrity of larval sea urchins (Heliocidaris crassispina). Notably, the negative impacts of fluoxetine exposure were attenuated by reduced pH. Larvae exposed to both reduced pH and fluoxetine exhibited lower levels of DNA damage compared to those exposed to only one of the stressors. Similar antagonistic interactions were observed at the organismal level: for example, fluoxetine exposure at 10 ng L^-1 under ambient pH increased the percentage of embryos at later developmental stages, but such effects of fluoxetine were absent at pH 7.7. However, despite the modulation of fluoxetine impacts under ocean acidification, control larvae performed better than those exposed to either stressor, alone or in combination. We also observed that pH alone impacted organismal behaviors, as larvae swam slower at reduced pH regardless of fluoxetine exposure. Our findings highlight the need to consider multi-stressor interactions when determining future organismal performance and that multiple metrics are needed to paint a fuller picture of ecological risks.

CO2-driven seawater acidification increases cadmium toxicity in a marine copepod

Here, we examined the 48-h acute toxicity of cadmium (Cd) in the marine copepod Tigriopus japonicus under two pCO₂ concentrations (400 and 1000 μatm). Subsequently, T. japonicus was interactively exposed to different pCO₂ (400, 1000 μatm) and Cd (control, 500 μg/L) treatments for 48 h. After exposure, biochemical and physiological responses were analyzed for the copepods. The results showed that the 48-h LC₅₀ values of Cd were calculated as 12.03 mg/L and 9.08 mg/L in T. japonicus, respectively, under 400 and 1000 μatm pCO₂ conditions. Cd exposure significantly promoted Cd exclusion/glycolysis, detoxification/stress response, and oxidative stress/apoptosis while it depressed that of antioxidant capacity. Intriguingly, CO₂-driven acidification enhanced Cd bioaccumulation and its toxicity in T. japonicus. Overall, our study provides a mechanistic understanding about the interaction between seawater acidification and Cd pollution in marine copepods.

Microplastic ingestion induces asymmetry and oxidative stress in larvae of the sea urchin Pseudechinus huttoni

Determining the effects of microplastic (MP) ingestion by marine organisms, especially during the sensitive larval stages, is an important step in understanding wider ecosystem responses. We investigated the ingestion, retention (1-5 μm), and short-term exposure effects (1-4 μm) of spherical MPs by larvae of the sea urchin Pseudechinus huttoni. Larvae ingested MPs in a dose-dependent manner and successfully egested particles after a short retention period. Survival was not significantly affected by exposure to MPs over the 10-day experimental period, however, a teratogenic response in terms of delayed development resulted in an increase of larval arm asymmetry. Additionally, MP exposure resulted in oxidative damage to lipids and proteins in larval body tissue despite a significant upregulation of antioxidant defences. The findings indicate MP exposure may impair cellular function, leading to negative consequences for an organism's fitness and survival.

Impact on Fertility Rate and Embryo-Larval Development Due to the Association Acidification, Ocean Warming and Lead Contamination of a Sea Urchin Echinometra lucunter (Echinodermata: Echinoidea)

Ocean warming and acidification can cause deleterious effects on marine biota, which may be potentialized when associated with metal pollution. Thus, the aim of this work was to evaluate the effects of pH decrease, temperature increase and lead contamination on fertility rate and embryo-larval development of Echinometra lucunter. Gametes and embryos were exposed at pH 8.2 (control) and 7.5; at 26°C (control) and 28°C; and at lead concentrations of 0 (control), 125, 250 and 500 μg/L. These conditions were tested individually and in combination. The fertilization rate of E. lucunter was only significantly reduced in the treatments where temperature was increased and in the treatment where pH decreased. However, the development rate of the pluteus larvae was significantly affected in the majority of treatments: metal contamination in the higher concentration; decreased pH in all metal concentrations; increased temperature in the highest metal concentration; decreased pH and increased temperature and all variables combined, which is decreased pH, increased temperature and metal contamination in relation to the control group (C). The development test was shown to be more sensitive than the fertilization test in all the studied scenarios. In general, the present study suggests that pH decrease, temperature increase and metal pollution may have a significant impact on E. lucunter reproductive cycle.

Impacts of Plastic-Made Packaging on Marine Key Species: Effects Following Water Acidification and Ecological Implications

This study evaluates the impacts of 16 different leachates of plastic-made packaging on marine species of different trophic levels (bacteria, algae, echinoderms). Standard ecotoxicological endpoints (inhibition of bioluminescence, inhibition of growth, embryo-toxicity) and alterations of ecologically significant parameters (i.e., echinoderms’ body-size) were measured following exposure under different pH water conditions: marine standard (pH 8.1) and two increasingly acidic conditions (pH 7.8 and 7.5) in order to evaluate possible variations induced by ocean acidification. The results obtained in this study evidence that the tested doses are not able to significantly affect bacteria (Vibrio fischeri) and algae (Phaeodactylum tricornutum). On the contrary, Paracentrotus lividus larvae were significantly affected by several packaging types (13 out of 16) with meaningless differences between pH conditions.

Gene Expression Changes after Parental Exposure to Metals in the Sea Urchin Affect Timing of Genetic Programme of Embryo Development

It is widely accepted that phenotypic traits can be modulated at the epigenetic level so that some conditions can affect the progeny of exposed individuals. To assess if the exposure of adult animals could result in effects on the offspring, the Mediterranean sea urchin and its well-characterized gene regulatory networks (GRNs) was chosen as a model. Adult animals were exposed to known concentrations of zinc and cadmium (both individually and in combination) for 10 days, and the resulting embryos were followed during the development. The oxidative stress occurring in parental gonads, embryo phenotypes and mortality, and the expression level of a set of selected genes, including members of the skeletogenic and endodermal GRNs, were evaluated. Increased oxidative stress at F₀, high rates of developmental aberration with impaired gastrulation, in association to deregulation of genes involved in skeletogenesis (dri, hex, sm50, p16, p19, msp130), endodermal specification (foxa, hox11/13b, wnt8) and epigenetic regulation (kat2A, hdac1, ehmt2, phf8 and UBE2a) occurred either at 24 or 48 hpf. Results strongly indicate that exposure to environmental pollutants can affect not only directly challenged animals but also their progeny (at least F₁), influencing optimal timing of genetic programme of embryo development, resulting in an overall impairment of developmental success.

The effect of ocean acidification on the enzyme activity of Apostichopus japonicus

The influence of ocean acidification (OA) is particularly significant on calcifying organisms. The sea cucumber Apostichopus japonicus is an important cultured calcifying organism in the northern China seas. Little was known about the effects of OA on this economically important species. In this study, individuals from embryo to juveniles stage of A. japonicus, cultured in different levels of acidified seawater, were measured their enzymes activities, including five metabolic enzymes and three immune enzymes. The activity of acid phosphatase (ACP) and alkaline phosphatase (ALP) was significantly lower in the severely acid group (pH 7.1), while the content of lactate dehydrogenase (LDH) was significantly higher. Superoxide dismutase (SOD) and catalase (CAT) were significantly lower in the severely acid group. The multivariate statistical results showed that the significant difference of enzyme assemblage existed among three experimental groups. This study indicated that OA could reduce the biomineralization capacity, influence the anaerobic metabolism and severely affect the immune process of A. japonicas. More researches are needed in the future to reveal the mechanisms of enzyme regulation and expression of A. japonicas underlying mixture environmental stress.

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.

Rapid deep ocean deoxygenation and acidification threaten life on Northeast Pacific seamounts

Anthropogenic climate change is causing our oceans to lose oxygen and become more acidic at an unprecedented rate, threatening marine ecosystems and their associated animals. In deep-sea environments, where conditions have typically changed over geological timescales, the associated animals, adapted to these stable conditions, are expected to be highly vulnerable to any change or direct human impact. Our study coalesces one of the longest deep-sea observational oceanographic time series, reaching back to the 1960s, with a modern visual survey that characterizes almost two vertical kilometers of benthic seamount ecosystems. Based on our new and rigorous analysis of the Line P oceanographic monitoring data, the upper 3,000 m of the Northeast Pacific (NEP) has lost 15% of its oxygen in the last 60 years. Over that time, the oxygen minimum zone (OMZ), ranging between approximately 480 and 1,700 m, has expanded at a rate of 3.0 ± 0.7 m/year (due to deepening at the bottom). Additionally, carbonate saturation horizons above the OMZ have been shoaling at a rate of 1-2 m/year since the 1980s. Based on our visual surveys of four NEP seamounts, these deep-sea features support ecologically important taxa typified by long life spans, slow growth rates, and limited mobility, including habitat-forming cold water corals and sponges, echinoderms, and fish. By examining the changing conditions within the narrow realized bathymetric niches for a subset of vulnerable populations, we resolve chemical trends that are rapid in comparison to the life span of the taxa and detrimental to their survival. If these trends continue as they have over the last three to six decades, they threaten to diminish regional seamount ecosystem diversity and cause local extinctions. This study highlights the importance of mitigating direct human impacts as species continue to suffer environmental changes beyond our immediate control.

Ocean acidification, hypoxia and warming impair digestive parameters of marine mussels

Global change and anthropogenic activities have driven marine environment changes dramatically during the past century, and hypoxia, acidification and warming have received much attention recently. Yet, the interactive effects among these stressors on marine organisms are extremely complex and not accurately clarified. Here, we evaluated the combined effects of low dissolved oxygen (DO), low pH and warming on the digestive enzyme activities of the mussel Mytilus coruscus. In this experiment, mussels were exposed to eight treatments, including two degrees of pH (8.1, 7.7), DO (6, 2 mg/l) and temperature (30 °C and 20 °C) for 30 days. Amylase (AMS), lipase (LPS), trypsin (TRY), trehalase (TREH) and lysozyme (LZM) activities were measured in the digestive glands of mussels. All the tested stress conditions showed significant effects on the enzymatic activities. AMS, LPS, TRY, TREH showed throughout decreased trend in their activities due to low pH, low DO, increased temperature and different combinations of these three stressors with time but LZM showed increased and then decreased trend in their activities. Hypoxia and warming showed almost similar effects on the enzymatic activities. PCA showed a positive correlation among all measured biochemical parameters. Therefore, the fitness of mussel is likely impaired by such marine environmental changes and their population may be affected under the global change scenarios.

Specialized adaptations allow vent-endemic crabs (Xenograpsus testudinatus) to thrive under extreme environmental hypercapnia

Shallow hydrothermal vent environments are typically very warm and acidic due to the mixing of ambient seawater with volcanic gasses (> 92% CO₂) released through the seafloor making them potential ‘natural laboratories’ to study long-term adaptations to extreme hypercapnic conditions. Xenograpsus testudinatus, the shallow hydrothermal vent crab, is the sole metazoan inhabitant endemic to vents surrounding Kueishantao Island, Taiwan, where it inhabits waters that are generally pH 6.50 with maximum acidities reported as pH 5.50. This study assessed the acid–base regulatory capacity and the compensatory response of X. testudinatus to investigate its remarkable physiological adaptations. Hemolymph parameters (pH, [HCO₃⁻], \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{P}}_{{{\text{CO}}_{2} }}$$\end{document}PCO2, [NH₄⁺], and major ion compositions) and the whole animal’s rates of oxygen consumption and ammonia excretion were measured throughout a 14-day acclimation to pH 6.5 and 5.5. Data revealed that vent crabs are exceptionally strong acid–base regulators capable of maintaining homeostatic pH against extreme hypercapnia (pH 5.50, 24.6 kPa \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{P}}_{{{\text{CO}}_{2} }}$$\end{document}PCO2) via HCO₃⁻/Cl⁻ exchange, retention and utilization of extracellular ammonia. Intact crabs as well as their isolated perfused gills maintained \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{P}}_{{{\text{CO}}_{2} }}$$\end{document}PCO2tensions below environmental levels suggesting the gills can excrete CO₂ against a hemolymph-directed \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{P}}_{{{\text{CO}}_{2} }}$$\end{document}PCO2 gradient. These specialized physiological mechanisms may be amongst the adaptations required by vent-endemic animals surviving in extreme conditions.

Cuttlefish Buoyancy in Response to Food Availability and Ocean Acidification

Carbon dioxide concentration in the atmosphere is expected to continue rising by 2100, leading to a decrease in ocean pH in a process known as ocean acidification (OA). OA can have a direct impact on calcifying organisms, including on the cuttlebone of the common cuttlefish Sepia officinalis. Moreover, nutritional status has also been shown to affect the cuttlebone structure and potentially affect buoyancy. Here, we aimed to understand the combined effects of OA (980 μatm CO2) and food availability (fed vs. non-fed) on the buoyancy of cuttlefish newborns and respective cuttlebone weight/area ratio (as a proxy for calcification). Our results indicate that while OA elicited negative effects on hatching success, it did not negatively affect the cuttlebone weight/area ratio of the hatchlings-OA led to an increase in cuttlebone weight/area ratio of fed newborns (but not in unfed individuals). The proportion of "floating" (linked to buoyancy control loss) newborns was greatest under starvation, regardless of the CO2 treatment, and was associated with a drop in cuttlebone weight/area ratio. Besides showing that cuttlefish buoyancy is unequivocally affected by starvation, here, we also highlight the importance of nutritional condition to assess calcifying organisms' responses to ocean acidification.

A scientometric review of the research on the impacts of climate change on water quality during 1998-2018

Research on the impacts of climate change on water quality helps to better formulate water quality strategies under the challenge of an uncertain future, which is critical for human survival and development. As a result, in recent years, there has been growing attention given to research in the field, and the attention has led to an increasing number of publications, which is why a systematic literature review on this topic has been proposed in the current paper. This study reviewed 2998 related articles extracted from the Science Citation Index-Expanded (SCI-E) database from 1998 to 2018 to analyse and visualize historical trend evolution, current research hotspots, and promising ideas for future research by combining a traditional literature review, bibliometric analysis, and scientific knowledge mapping. The results revealed that the impacts of climate change on water quality mainly included the aggravation of eutrophication, changes in the flow, hydrological and thermal conditions, and the destruction of ecosystems and biodiversity. Further exploration of the influence mechanism of climate change on cyanobacteria is an emerging research topic. Additionally, the water quality conditions of shallow lakes and drinking water are promising future research objects. In the context of climate change, the general rules of water quality management and the scientific planning of land use are of great significance and need to be further studied. This study provides a practical and valuable reference for researchers to help with the selection of future research topics, which may contribute to further development in this field.

Transgenerational acclimation to changes in ocean acidification in marine invertebrates

The rapid pace of increasing oceanic acidity poses a major threat to the fitness of the marine ecosystem, as well as the buffering capacity of the oceans. Disruption in chemical equilibrium in the ocean leads to decreased carbonate ion precipitation, resulting in calcium carbonate saturation. If these trends continue, calcifying invertebrates will experience difficultly maintaining their calcium carbonate exoskeleton and shells. Because malfunction of exoskeleton formation by calcifiers in response to ocean acidification (OA) will have non-canonical biological cascading results in the marine ecosystem, many studies have investigated the direct and indirect consequences of OA on ecosystem- and physiology-related traits of marine invertebrates. Considering that evolutionary adaptation to OA depends on the duration of OA effects, long-term exposure to OA stress over multi-generations may result in adaptive mechanisms that increase the potential fitness of marine invertebrates in response to OA. Transgenerational studies have the potential to elucidate the roles of acclimation, carryover effects, and evolutionary adaptation within and over generations in response to OA. In particular, understanding mechanisms of transgenerational responses (e.g., antioxidant responses, metabolic changes, epigenetic reprogramming) to changes in OA will enhance our understanding of marine invertebrate in response to rapid climate change.

CO2-driven ocean acidification repressed the growth of adult sea urchin Strongylocentrotus intermedius by impairing intestine function

Strongylocentrotus intermedius cultured in the northern Yellow Sea in China was utilized to evaluate the effects of chronic CO₂-driven ocean acidification (OA) on adult sea urchins. Based on the projection of the Intergovernmental Panel on Climate Change (IPCC), present natural seawater conditions (pH_NBS = 8.10 ± 0.03) and three laboratory-controlled OA conditions (OA₁, ΔpH_NBS = - 0.3 units; OA₂, ΔpH_NBS = - 0.4 units; OA₃, ΔpH_NBS = - 0.5 units) were employed. After 60-day incubation, our results showed that (1) OA significantly repressed the growth of adult S. intermedius; (2) food consumption tended to be decreased with pH decline; (3) intestinal morphology was changed, and activities of intestinal cellulase and lipase were decreased under acidified conditions; (4) expression levels of two immune-related genes (SiTNF14 and SiTGF-β) were altered; (5) rate-limiting enzyme activities of the glycolytic pathway and tricarboxylic acid cycle (TAC) were changed in all OA treatments compared to those of controls.

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.

The effect of ocean acidification on the intertidal hermit crab Pagurus criniticornis is not modulated by cheliped amputation and sex

Impacts of the interactive effects of ocean acidification (OA) with other anthropogenic environmental stressors on marine biodiversity are receiving increasing attention in recent years. However, little is known about how organismal responses to OA may be influenced by common phenomena such as autotomy and sexual dimorphism. This study evaluated the long-term (120 days) combined effects of OA (pH 7.7), experimental cheliped amputation and sex on physiological stress (mortality, growth, number of molts, cheliped regeneration and startle response) and energy budget (lipid and calcium contents) in the intertidal sexually-dimorphic hermit crab Pagurus criniticornis. Crabs exposed to OA reduced survivorship (46%), molting frequency (36%) and lipid content (42%). Autotomised crabs and males molted more frequently (39% and 32%, respectively). Males presented higher regeneration (33%) and lower lipid content (24%). The few synergistic effects recorded did not indicate any clear pattern among treatments however, (1) a stronger reduction in lipid content was recorded in non-autotomised crabs exposed to low pH; (2) calcium content was higher in males than females only for autotomised crabs under control pH; and (3) autotomised females showed a proportionally slower activity recovery than autotomised males. Although our results suggest an effect of long-term exposure to low pH on the physiological stress and energy budget of Pagurus criniticornis, the physiological repertoire and plasticity associated with limb regeneration and the maintenance of dimorphism in secondary sexual characters may provide resilience to long-term exposure to OA.

Exposure of key marine species to sunscreens: Changing ecotoxicity as a possible indirect effect of global warming

Sunscreens can induce ecotoxicological effects and may cause significant impacts in the aquatic ecosystem. In spite of that, ecotoxicological responses of key marine species to sunscreens are scarcely studied in Mediterranean ecosystems, and literature data are lacking. Furthermore, changes in water salinity induced by global warming could significantly affect the ecotoxicological responses of marine species exposed to sunscreens. This research focuses on the evaluation of ecotoxicological responses of Phaeodactylum tricornutum (algae), Corophium orientalis (macroinvertebrate), and Paracentrotus lividus (echinoderms) exposed to sunscreens, which include both chemical- and physical-based. This study, also, analyzes the changes in ecotoxicological responses of the tested species linked to increase in salinity. Results showed that salinity stress significantly increases the toxicity of sunscreens on the tested marine species. Physical-based sunscreens resulted in more toxicity at higher salinity than chemical-based ones toward C. orientalis and P. tricornutum. This study evidenced that risk classifications of sunscreens recorded under standard salinity conditions could be significantly different from that recorded in the natural environment under salinity stress. The collection of a complete dataset on the ecotoxicological effects of sunscreens on marine species tested under salinity stress could be useful to correctly weigh risks for the marine environment under possible future ecological changing scenarios following the global changing driver.

Complex and interactive effects of ocean acidification and warming on the life span of a marine trematode parasite

Human activities have caused an increase in atmospheric CO₂ over the last 250 years, leading to unprecedented rates of change in seawater pH and temperature. These global scale processes are now commonly referred to as ocean acidification and warming, and have the potential to substantially alter the physiological performance of many marine organisms. It is vital that the effects of ocean acidification and warming on marine organisms are explored so that we can predict how marine communities may change in future. In particular, the effect of ocean acidification and warming on host-parasite dynamics is poorly understood, despite the ecological importance of these relationships. Here, we explore the response of one himasthlid trematode, Himasthla sp., an abundant and broadly distributed species of marine parasite, to combinations of elevated temperature and pCO₂ that represent physiological extremes, pre-industrial conditions, and end of century predictions. Specifically, we quantified the life span of the free-living cercarial stage under elevated temperature and pCO₂, focussing our research on functional life span (the time cercariae spend actively swimming) and absolute life span (the period before death). We found that the effects of temperature and pCO₂ were complex and interactive. Overall, increased temperature negatively affected functional and absolute life span, e.g. across all pCO₂ treatments the average time to 50% cessation of active swimming was approximately 8 h at 5 °C, 6 h at 15 °C, 4 h at 25 °C, and 2 h at 40 °C. The effect of pCO₂, which significantly affected absolute life span, was highly variable across temperature treatments. These results strongly suggest that ocean acidification and warming may alter the transmission success of trematode cercariae, and potentially reduce the input of cercariae to marine zooplankton. Either outcome could substantially alter the community structure of coastal marine systems.

Description and ecophysiology of a new species of Syndesmis Silliman, 1881 (Rhabdocoela: Umagillidae) from the sea urchin Evechinus chloroticus (Valenciennes, 1846) Mortensen, 1943 in New Zealand

A new rhabdocoel of the genus Syndesmis Silliman, 1881 (Umagillidae) is described from the intestine of the New Zealand sea urchin Evechinus chloroticus (Valenciennes, 1846) Mortensen, 1943a. This new species, Syndesmis kurakaikina n. sp., is morphologically distinct and can easily be recognised by its very long (±1 mm) stylet and its bright-red colour. In addition to providing a formal description, we present some observations on reproduction and life history of this new species. Fecundity is comparable to that of other umagillids and the rate of egg production and development increases with temperature. Hatching in this species is induced by intestinal fluids of its host. Relevant to global warming, we assessed the effect of temperature on survival, fecundity, and development. The tests indicate that Syndesmis kurakaikina n. sp. is tolerant of a wide range of temperatures (11-25 °C) and that its temperature optimum lies between 18.0 and 21.5 °C. Egg viability is, however, significantly compromised at the higher end of this temperature range, with expelled egg capsules often being deformed and showing increasingly lower rates of hatching. Given this, a rise in global temperature might increase the risk of Syndesmis kurakaikina n. sp. infecting new hosts and would possibly facilitate the spread of these endosymbionts.

Measurement of feeding rates, respiration, and pH regulatory processes in the light of ocean acidification research

The physiology of marine larvae has received considerable attention in the context of anthropogenic ocean acidification (OA). Many marine larvae including those of echinoderms, hemichordates, and mollusks are characterized by a developmental delay when exposed to reductions in seawater pH with the underlying mechanisms being largely unexplored. A key task in the frame of OA research lies in the identification of unifying physiological principles that may explain reductions in growth and development. The sea urchin larva has been identified as a good model organism, and energy allocations toward compensatory processes were found to be key factors affecting development. However, physiological approaches to assess the animal's energy budget, as well as methods to characterize energy consuming processes (e.g., gut pH homeostasis and biomineralization) were scarce. During the last decade, a suite of physiological techniques was developed, to accurately determine the larval energy budget including feeding and metabolic rate measurements. To identify and characterize energy consuming processes, gastroscopic pH measurements in the larval gut and intracellular pH measurements of primary mesenchyme cells were developed. These techniques helped to understand fundamental processes of gut homeostasis and biomineralization in the developing sea urchin larva and their interaction with the environment. Using the sea urchin larva as a model these methods were successfully transferred to other echinoderm and hemichordate early developmental stages. This chapter explains and provides the methodological basis for the determination of feeding and metabolic rates as well as intracellular and extracellular pH measurements using the sea urchin larva as an example.

Effects of ocean warming and acidification on fertilization success and early larval development in the green sea urchin Lytechinus variegatus

Ocean acidification and warming are predicted to affect the early life of many marine organisms, but their effects can be synergistic or antagonistic. This study assessed the combined effects of near-future (2100) ocean acidification (pH 7.8) and warming (+3 °C) on the fertilization, larval development and growth of the green sea urchin, Lytechinus variegatus, common in tropical reefs of Florida and the Caribbean. Acidification had no effect on fertilization, but delayed larval development, stunted growth, and increased asymmetry. Warming decreased fertilization success when the sperm:egg ratio was higher (1847:1), accelerated larval development, but had no effect on growth. When exposed to both acidification and warming, fertilization rates decreased, larval development accelerated (due to increased respiration/metabolism), but larvae were smaller and more asymmetric, meaning acidification and warming had additive effects. Thus, climate change is expected to decrease the abundance of this important herbivore, exacerbating macroalgal growth and dominance on coral reefs.

The importance of inter-individual variation in predicting species' responses to global change drivers

Inter-individual variation in phenotypic traits has long been considered as "noise" rather than meaningful phenotypic variation, with biological studies almost exclusively generating and reporting average responses for populations and species' average responses. Here, we compare the use of an individual approach in the investigation of extracellular acid-base regulation by the purple sea urchin Paracentrotus lividus challenged with elevated pCO2 and temperature conditions, with a more traditional approach which generates and formally compares mean values. We detected a high level of inter-individual variation in acid-base regulation parameters both within and between treatments. Comparing individual and mean values for the first (apparent) dissociation constant of the coelomic fluid for individual sea urchins resulted in substantially different (calculated) acid-base parameters, and models with stronger statistical support. While the approach using means showed that coelomic pCO2 was influenced by seawater pCO2 and temperature combined, the individual approach indicated that it was in fact seawater temperature in isolation that had a significant effect on coelomic pCO2. On the other hand, coelomic [HCO3 -] appeared to be primarily affected by seawater pCO2, and less by seawater temperature, irrespective of the approach adopted. As a consequence, we suggest that individual variation in physiological traits needs to be considered, and where appropriate taken into account, in global change biology studies. It could be argued that an approach reliant on mean values is a "procedural error." It produces an artefact, that is, a population's mean phenotype. While this may allow us to conduct relatively simple statistical analyses, it will not in all cases reflect, or take into account, the degree of (physiological) diversity present in natural populations.

Bottom-up effects on biomechanical properties of the skeletal plates of the sea urchin Paracentrotus lividus (Lamarck, 1816) in an acidified ocean scenario

Sea urchins, ecologically important herbivores of shallow subtidal temperate reefs, are considered particularly threatened in a future ocean acidification scenario, since their carbonate structures (skeleton and grazing apparatus) are made up of the very soluble high-magnesium calcite, particularly sensitive to a decrease in pH. The biomechanical properties of their skeletal structures are of great importance for their individual fitness, because the skeleton provides the means for locomotion, grazing and protection from predators. Sea urchin skeleton is composed of discrete calcite plates attached to each other at sutures by organic ligaments. The present study addressed the fate of the sea urchin Paracentrotus lividus (Lamarck, 1816) skeleton in acidified oceans, taking into account the combined effect of reduced pH and macroalgal diet, with potential cascading consequences at the ecosystem level. A breaking test on individual plates of juvenile specimens fed different macroalgal diets has been performed, teasing apart plate strength and stiffness from general robustness. Results showed no direct short-term effect of a decrease in seawater pH nor of the macroalgal diet on single plate mechanical properties. Nevertheless, results from apical plates, the ones presumably formed during the experimental period, provided an indication of a possible diet-mediated response, with sea urchins fed the more calcified macroalga sustaining higher forces before breakage than the one fed the non-calcified algae. This, on the long term, may produce bottom-up effects on sea urchins, leading to potential shifts in the ecosystem equilibrium under an ocean acidified scenario.

Aberrant gene expression profiles in Mediterranean sea urchin reproductive tissues after metal exposures

Marine organisms are simultaneously exposed to numerous pollutants, among which metals probably represent the most abundant in marine environments. In order to evaluate the effects of metal exposure at molecular level in reproductive tissues, we profiled the sea urchin transcriptional response after non-lethal exposures using pathway-focused mRNA expression analyses. Herein, we show that exposures to relatively high concentrations of both essential and toxic metals hugely affected the gonadic expression of several genes involved in stress-response, detoxification, transcriptional and post-transcriptional regulation, without significant changes in gonadosomatic indices. Even though treatments did not result in reproductive tissues visible alterations, metal exposures negatively affected the main mechanisms of stress-response, detoxification and survival of adult P. lividus. Additionally, transcriptional changes observed in P. lividus gonads may cause altered gametogenesis and maintenance of heritable aberrant epigenetic effects. This study leads to the conclusion that exposures to metals, as usually occurs in polluted coastal areas, may affect sea urchin gametogenesis, thus supporting the hypothesis that parental exposure to environmental stressors affects the phenotype of the offspring.

Culturing echinoderm larvae through metamorphosis

Echinoderms are favored study organisms not only in cell and developmental biology, but also physiology, larval biology, benthic ecology, population biology and paleontology, among other fields. However, many echinoderm embryology labs are not well-equipped to continue to rear the post-embryonic stages that result. This is unfortunate, as such labs are thus unable to address many intriguing biological phenomena, related to their own cell and developmental biology studies, that emerge during larval and juvenile stages. To facilitate broader studies of post-embryonic echinoderms, we provide here our collective experience rearing these organisms, with suggestions to try and pitfalls to avoid. Furthermore, we present information on rearing larvae from small laboratory to large aquaculture scales. Finally, we review taxon-specific approaches to larval rearing through metamorphosis in each of the four most commonly-studied echinoderm classes-asteroids, echinoids, holothuroids and ophiuroids.

Physiological and biochemical responses of a coralline alga and a sea urchin to climate change: Implications for herbivory

Direct responses to rising temperatures and ocean acidification are increasingly well known for many single species, yet recent reviews have highlighted the need for climate change research to consider a broader range of species, how stressors may interact, and how stressors may affect species interactions. The latter point is important in the context of plant-herbivore interactions, as increasing evidence shows that increasing seawater temperature and/or acidification can alter algal traits that dictate their susceptibility to herbivores, and subsequently, community and ecosystem properties. To better understand how marine rocky shore environments will be affected by a changing ocean, in the present study we investigated the direct effects of short-term, co-occurring increased temperature and ocean acidification on a coralline alga (Jania rubens) and a sea urchin herbivore (Echinometra lucunter) and assessed the indirect effects of these factors on the algal-herbivore interaction. A 21-day mesocosm experiment was conducted with both algae and sea urchins exposed to ambient (24 °C, Low CO₂), high-temperature (28 °C, Low CO₂), acidified (24 °C, High CO₂), or high-temperature plus acidified (28 °C, High CO₂) conditions. Algal photosynthesis, respiration, and phenolic content were unaffected by increased temperature and CO₂, but calcium carbonate content was reduced under high CO₂ treatments in both temperatures, while total sugar content of the algae was reduced under acidified, lower temperature conditions. Metabolic rates of the sea urchin were elevated in the lower temperature, high CO₂ treatment, and feeding assays showed that consumption rates also increased in this treatment. Despite some changes to algal chemical composition, it appears that at least under short-term exposure to climate change conditions, direct effects on herbivore metabolism dictated herbivory rates, while indirect effects caused by changes in algal palatability seemed to be of minor importance.

Generality in multispecies responses to ocean acidification revealed through multiple hypothesis testing

Decades of research have demonstrated that many calcifying species are negatively affected by ocean acidification, a major anthropogenic threat in marine ecosystems. However, even closely related species may exhibit different responses to ocean acidification and less is known about the drivers that shape such variation in different species. Here, we examine the drivers of physiological performance under ocean acidification in a group of five species of turf-forming coralline algae. Specifically, quantitating the relative weight of evidence for each of ten hypotheses, we show that variation in coralline calcification and photosynthesis was best explained by allometric traits. Across ocean acidification conditions, larger individuals (measured as noncalcified mass) had higher net calcification and photosynthesis rates. Importantly, our approach was able to not only identify the aspect of size that drove the performance of coralline algae, but also determined that responses to ocean acidification were not dependent on species identity, evolutionary relatedness, habitat, shape, or structural composition. In fact, we found that failure to test multiple, alternative hypotheses would underestimate the generality of physiological performances, leading to the conclusion that each species had different baseline performance under ocean acidification. Testing among alternative hypotheses is an essential step toward determining the generalizability of experiments across taxa and identifying common drivers of species responses to global change.

Trans-life cycle acclimation to experimental ocean acidification affects gastric pH homeostasis and larval recruitment in the sea star Asterias rubens

AIM

Experimental simulation of near-future ocean acidification (OA) has been demonstrated to affect growth and development of echinoderm larval stages through energy allocation towards ion and pH compensatory processes. To date, it remains largely unknown how major pH regulatory systems and their energetics are affected by trans-generational exposure to near-future acidification levels.

METHODS

Here, we used the common sea star Asterias rubens in a reciprocal transplant experiment comprising different combinations of OA scenarios, to study trans-generational plasticity using morphological and physiological endpoints.

RESULTS

Acclimation of adults to pH_T 7.2 (pCO₂ 3500 μatm) led to reductions in feeding rates, gonad weight and fecundity. No effects were evident at moderate acidification levels (pH_T 7.4; pCO₂ 2000 μatm). Parental pre-acclimation to pH_T 7.2 for 85 days reduced developmental rates even when larvae were raised under moderate and high pH conditions, whereas pre-acclimation to pH_T 7.4 did not alter offspring performance. Microelectrode measurements and pharmacological inhibitor studies carried out on larval stages demonstrated that maintenance of alkaline gastric pH represents a substantial energy sink under acidified conditions that may contribute up to 30% to the total energy budget.

CONCLUSION

Parental pre-acclimation to acidification levels that are beyond the pH that is encountered by this population in its natural habitat (eg, pH_T 7.2) negatively affected larval size and development, potentially through reduced energy transfer. Maintenance of alkaline gastric pH and reductions in maternal energy reserves probably constitute the main factors for a reduced juvenile recruitment of this marine keystone species under simulated OA.

Physiological and Behavioral Plasticity of the Sea Cucumber Holothuria forskali (Echinodermata, Holothuroidea) to Acidified Seawater

Research into the effects of reduced pH caused by rising CO2 on echinoderms has been strongly biased toward those groups which rely heavily on calcification, such as sea urchins. There is very limited information available for groups that are less reliant on calcification, such as sea cucumbers. Moreover, plasticity in physiology and behavior in holothurians, which is considered to be critical to cope with ocean acidification, remains even less understood. Here, we examined the effects of a 22-week exposure to three pH levels (pH 7.97, 7.88, and 7.79) on the responses of adult Holothuria forskali. This is an abundant and ecologically important sea cucumber in shallow waters of the northeast Atlantic and Mediterranean. The holothurians did not exhibit serious acidosis after a 4-week gradually decreased pH exposure, possibly due to the slow acclimation period. After an additional 18 weeks of exposure, coelomic acid-base parameters did not differ significantly among the pH treatments, whereas they were higher than in week 4. Gonad development, defense behavior, and the structure and Ca2+ and Mg2+ concentrations of calcareous endoskeleton deposited in the body wall were all unaffected by decreased levels of seawater pH. No statistical differences were found after 22 weeks, and adult H. forskali showed strong physiological and behavioral plasticity to the effects of lowered seawater pH. While the interpretation of our results is restricted due to small sample sizes, this first long-term study of the effects of seawater acidification on sea cucumbers revealed resilience within the wide natural range of pCO2 found in NE Atlantic coastal waters.

Variability in larval gut pH regulation defines sensitivity to ocean acidification in six species of the Ambulacraria superphylum

The unusual rate and extent of environmental changes due to human activities may exceed the capacity of marine organisms to deal with this phenomenon. The identification of physiological systems that set the tolerance limits and their potential for phenotypic buffering in the most vulnerable ontogenetic stages become increasingly important to make large-scale projections. Here, we demonstrate that the differential sensitivity of non-calcifying Ambulacraria (echinoderms and hemichordates) larvae towards simulated ocean acidification is dictated by the physiology of their digestive systems. Gastric pH regulation upon experimental ocean acidification was compared in six species of the superphylum Ambulacraria. We observed a strong correlation between sensitivity to ocean acidification and the ability to regulate gut pH. Surprisingly, species with tightly regulated gastric pH were more sensitive to ocean acidification. This study provides evidence that strict maintenance of highly alkaline conditions in the larval gut of Ambulacraria early life stages may dictate their sensitivity to decreases in seawater pH. These findings highlight the importance of identifying and understanding pH regulatory systems in marine larval stages that may contribute to substantial energetic challenges under near-future ocean acidification scenarios.

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

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