Acidification reduced growth rate but not swimming speed of larval sea urchins

Effect of elevated temperature, sea water acidification, and phenanthrene on the expression of genes involved in the shell and pearl formation of economic pearl oyster (Pinctada radiata)

Our study aims to examine the effect of some stressors on the gene expression levels of shell matrix proteins in a pearl oyster. Oysters were exposed to the different combinations of the temperature, pH, and phenanthrene concentration is currently measured in the Persian Gulf and the predicted ocean warming and acidification for 28 days. The expression of all the studied genes was significantly downregulated. Time and temperature had the greatest effects on the decreases in n19 and n16 genes expression, respectively. Aspein and msi60 genes expression were highly influenced by pH. Pearlin was affected by double interaction temperature and phenanthrene. Moreover, a correlation was observed among the expression levels of studied genes. This study represents basic data on the relationship between mRNA transcription genes involved in the shell and pearl formation and climate changes in pollutant presence conditions and acclimatizing mechanism of the oyster to the future scenario as well.

Whole-Genome Sequencing Reveals That Regulatory and Low Pleiotropy Variants Underlie Local Adaptation to Environmental Variability in Purple Sea Urchins

AbstractOrganisms experience environments that vary across both space and time. Such environmental heterogeneity shapes standing genetic variation and may influence species' capacity to adapt to rapid environmental change. However, we know little about the kind of genetic variation that is involved in local adaptation to environmental variability. To address this gap, we sequenced the whole genomes of 140 purple sea urchins (Strongylocentrotus purpuratus) from seven populations that vary in their degree of pH variability. Despite no evidence of global population structure, we found a suite of single-nucleotide polymorphisms (SNPs) tightly correlated with local pH variability (outlier SNPs), which were overrepresented in regions putatively involved in gene regulation (long noncoding RNA and enhancers), supporting the idea that variation in regulatory regions is important for local adaptation to variability. In addition, outliers in genes were found to be (i) enriched for biomineralization and ion homeostasis functions related to low pH response, (ii) less central to the protein-protein interaction network, and (iii) underrepresented among genes highly expressed during early development. Taken together, these results suggest that loci that underlie local adaptation to pH variability in purple sea urchins fall in regions with potentially low pleiotropic effects (based on analyses involving regulatory regions, network centrality, and expression time) involved in low pH response (based on functional enrichment).

Behavioral and physiological effects of ocean acidification and warming on larvae of a continental shelf bivalve

The negative impacts of ocean warming and acidification on bivalve fisheries are well documented but few studies investigate parameters relevant to energy budgets and larval dispersal. This study used laboratory experiments to assess developmental, physiological and behavioral responses to projected climate change scenarios using larval Atlantic surfclams Spisula solidissima solidissima, found in northwest Atlantic Ocean continental shelf waters. Ocean warming increased feeding, scope for growth, and biomineralization, but decreased swimming speed and pelagic larval duration. Ocean acidification increased respiration but reduced immune performance and biomineralization. Growth increased under ocean warming only, but decreased under combined ocean warming and acidification. These results suggest that ocean warming increases metabolic activity and affects larval behavior, while ocean acidification negatively impacts development and physiology. Additionally, principal component analysis demonstrated that growth and biomineralization showed similar response profiles, but inverse response profiles to respiration and swimming speed, suggesting alterations in energy allocation under climate change.

Developmental atlas of the indirect-developing sea urchin Paracentrotus lividus: From fertilization to juvenile stages

The sea urchin Paracentrotus lividus has been used as a model system in biology for more than a century. Over the past decades, it has been at the center of a number of studies in cell, developmental, ecological, toxicological, evolutionary, and aquaculture research. Due to this previous work, a significant amount of information is already available on the development of this species. However, this information is fragmented and rather incomplete. Here, we propose a comprehensive developmental atlas for this sea urchin species, describing its ontogeny from fertilization to juvenile stages. Our staging scheme includes three periods divided into 33 stages, plus 15 independent stages focused on the development of the coeloms and the adult rudiment. For each stage, we provide a thorough description based on observations made on live specimens using light microscopy, and when needed on fixed specimens using confocal microscopy. Our descriptions include, for each stage, the main anatomical characteristics related, for instance, to cell division, tissue morphogenesis, and/or organogenesis. Altogether, this work is the first of its kind providing, in a single study, a comprehensive description of the development of P. lividus embryos, larvae, and juveniles, including details on skeletogenesis, ciliogenesis, myogenesis, coelomogenesis, and formation of the adult rudiment as well as on the process of metamorphosis in live specimens. Given the renewed interest for the use of sea urchins in ecotoxicological, developmental, and evolutionary studies as well as in using marine invertebrates as alternative model systems for biomedical investigations, this study will greatly benefit the scientific community and will serve as a reference for specialists and non-specialists interested in studying sea urchins.

CO2 acidification and pandemic situation

This chapter reviews the situation of CO₂ acidification and its effects in aquatic ecosystems related to the pandemic situation associated with COVID-19, but also includes the effects of other infections such as malaria, dengue, etc., and the relationship between human health, ecosystem health, and risk assessment. The interactions between these processes (infection and CO₂ acidification) are compared and analyzed, and considerations about the role of these viruses and bacteria in the risk assessment will be commented on as part of the LoEs and WoEs discussed in the book. Some recent data about the influence of the pandemic on CO₂ emissions and the acidification in the aquatic ecosystem will be presented and discussed too.

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.

Interactive effects of increased temperature and gadolinium pollution in Paracentrotus lividus sea urchin embryos: a climate change perspective

Gradual ocean warming and marine heatwaves represent major threats for marine organisms already facing other anthropogenic-derived hazards, such as chemical contamination in coastal areas. In this study, the combined effects of thermal stress and exposure to gadolinium (Gd), a metal used as a contrasting agent in medical imaging which enters the aquatic environment, were investigated in the embryos and larvae of the sea urchin Paracentrotus lividus. Embryos were exposed to six treatments of three temperatures (18 °C, 21 °C, 24 °C) and two Gd concentrations (control: 0 μM; treated: 20 μM). With respect to developmental progression, increased temperature accelerated development and achievement of the larval stage, while Gd-exposed embryos at the control temperature (18 °C) showed a general delay in development at 24 h post-fertilization (hpf), and a stunting effect and impaired skeleton growth at 48 hpf. Elevated temperatures at near-future projections (+3 °C, 21 °C) reduced the negative effects of Gd on development with a lower percentage of abnormality and improved skeleton growth. Combined extreme warming at present-day marine heatwave conditions (+6 °C, 24 °C) and Gd treatment resulted in a lower proportion of embryos reaching the advanced larval stages compared to the 21 °C + Gd. At the molecular level, western blot analysis showed that Gd was the main driver for the induction of heat shock protein (HSP60, HSP70) expression. At 48 hpf, temperature increase was the main driver for activation of additional cellular stress response strategies such as autophagy and apoptosis. Combined treatments showed the induction of HSP60 at 24 hpf and autophagic and apoptotic processes at 48 hpf. Treatments having low levels of HSPs expression showed high levels of apoptosis, and vice versa, clearly demonstrating the antagonistic effects of HSPs expression and apoptosis. Detection of fragmented DNA in apoptotic nuclei showed selective apoptosis, likely in extremely damaged cells. Our results indicate that the negative effects of Gd-exposure on P. lividus larval development and biomineralization will be mitigated by a near-future ocean warming, up to a thermotolerance threshold when negative synergistic effects were evident. Our data highlight the use of biomarkers as sensitive tools to detect environmental impacts as well as the need for a better understanding of the interactions between the multiple stressors faced by marine species in coastal environments.

Oxidative stress and antioxidant defence responses in two marine copepods in a high CO2 experiment

We collected samples for oxidative stress and antioxidants in a high CO₂ mesocosm experiment for two weeks, focussing on two common crustacean copepods Calanus finmarchicus and Temora longicornis. The samples were collected during a field experiment campaign studying responses of plankton communities to future ocean acidification (OA), off the Norwegian coast south of Bergen. The main results showed that there were species-specific differences between Temora and Calanus, especially in antioxidant defences (glutathione system) and oxidative stress (lipid peroxidation and reduced:oxidised glutathione ratio). Regular monitoring of chlorophyll a and jellyfish abundances taking place during the field campaign revealed that both chl a and predators may have affected the eco-physiological response. Antioxidant and oxidative stress levels are known to respond sensitively to both the food quality and quantity and the predator pressure, apart from environmental (i.e., abiotic) changes. Calanus was more robust towards OA, perhaps due to its high tolerance to a wide range of vertical physical-chemical conditions. Both top-down and bottom-up factors seem to play a role for the outcome of copepod responses to future ocean acidification.

Impairment of swimming performance in Tritia reticulata (L.) veligers under projected ocean acidification and warming scenarios

Tritia reticulata (L.) is a neogastropod ubiquitous in the coastal communities of the NE Atlantic. Its life cycle relies on the swimming performance of planktonic early life stages, whose sensitivity to the climate conditions projected for the near future, namely of ocean acidification (OA) and warming (W), is, to our best knowledge, unknown. To examine the resilience of larval stages to future environmental conditions, this work investigates the effect of OA-W on the swimming performance of T. reticulata veligers under a range of experimental conditions, based on the end-of-century projections of the Intergovernmental Panel on Climate Change. Veligers were exposed to six experimental scenarios for 14 days, employing a full factorial design with three temperatures (T°C: 18, 20 and 22 °C) and two pH levels (pH_target: 8.1 and 7.8). Mortality was assessed throughout the trial, after which swimming behaviour - characterised by the activity, speed and the distance travelled by veligers - was analysed by automated video recordings in a Zebrabox® device. Mortality increased with OA-W and, although more active, larvae travelled shorter distances revealing reduced swimming speed under acidic and warmer conditions, with the interaction of the tested stressors - pH and T°C - being highly significant. Results motivated the morpho-histological analysis of larvae preserved at the end of the trial, to check for the integrity of the organs involved in veligers' motion: statocysts, velum and foot. Statocyst and velar morpho-structure were conserved but histological damage of metapodial epithelia was evident under acidity, namely an apparent hypertrophy and protrusion of the secretory cells, with dispersed pigmented granules and, at 22 °C, less cilia, with potential functional implications. Negative consequences of the OA-W scenarios tested on veligers' competence are unveiled, pointing towards the eminent threat these phenomena constitute to T. reticulata perpetuation in case no mitigation measures are taken, and projections become effective.

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.

Ocean acidification changes the vertical movement of stone crab larvae

Anthropogenic activities are increasing ocean temperature and decreasing ocean pH. Some coastal habitats are experiencing increases in organic runoff, which when coupled with a loss of vegetated coastline can accelerate reductions in seawater pH. Marine larvae that hatch in coastal habitats may not have the ability to respond to elevated temperature and changes in seawater pH. This study examined the response of Florida stone crab (Menippe mercenaria) larvae to elevated temperature (30°C control and 32°C treatment) and CO₂-induced reductions in pH (8.05 pH control and 7.80 pH treatment). We determined whether those singular and simultaneous stressors affect larval vertical movement at two developmental stages. Geotactic responses varied between larval stages. The direction and rate of the vertical displacement of larvae were dependent on pH rather than temperature. Stage III larvae swam upwards under ambient pH conditions, but swam downwards at a faster rate under reduced pH. There was no observable change in the directional movement of Stage V larvae. The reversal in orientation by Stage III larvae may limit larval transport in habitats that experience reduced pH and could pose challenges for the northward dispersal of stone crabs as coastal temperatures warm.

Intraspecific variation in the response of the estuarine European isopod Cyathura carinata (Krøyer, 1847) to ocean acidification

In the present study the model isopod, Cyathura carinata were exposed to four pH_NIST treatments (control: 7.9; 7.5, 7, 6.5) in order to determine the tolerance and pH threshold value this estuarine species withstand under future acidification scenarios. Seawater acidification significantly affected the lifespan of C. carinata, where population density was remarkably reduced at the lowest pH treatment. The longevity, survivorship and swimming activity (related to the acquisition of energy) of these isopods decreased with decreasing pH. Furthermore, to determine the possible metabolic plasticity of this species, the swimming activity, the Na+/K + -ATPase activity (relevant for osmoregulation process), and the RNA:DNA ratio (an indicator of fitness) were measure from two populations of C. carinata, one inhabiting a stable environment (pH_NIST 7.5-8.0) and one inhabiting a fluctuating pCO₂ regimes (pH 3.3-8.5) subjected to three pH treatments (7.9, 7.0 and 6.5). The population from high fluctuating pCO₂ conditions showed capacity to withstand to pH 6.5, as well as higher longevity and metabolic plasticity, when compared with the population from the habitat with slight pCO₂ variation. These results indicate that Cyathura population from stable environments could be vulnerable to ocean acidification because it could trigger detrimental effects on its survival energy budget, and growth. However, ocean acidification has limited effect on the energy budget and survival of C. carinata population from highly variable habitats, suggesting that they are able to cope with the elevated energy demand. The difference showed between populations is likely an indication of genetic differentiation in tolerance to ocean acidification, possibly attributable to local adaptations, which could provide the raw material necessary for adaptation to future conditions. In addition, our results suggest that when assessing marine crustacean responses to changing environments on a global scale, variability in population and metabolic responses need to be considered.

Genomic resources for the study of echinoderm development and evolution

Echinoderms are important research models for a wide range of biological questions. In particular, echinoderm embryos are exemplary models for dissecting the molecular and cellular processes that drive development and testing how these processes can be modified through evolution to produce the extensive morphological diversity observed in the phylum. Modern attempts to characterize these processes depend on some level of genomic analysis; from querying annotated gene sets to functional genomics experiments to identify candidate cis-regulatory sequences. Given how essential these data have become, it is important that researchers using available datasets or performing their own genome-scale experiments understand the nature and limitations of echinoderm genomic analyses. In this chapter we highlight the current state of echinoderm genomic data and provide methodological considerations for common approaches, including analysis of transcriptome and functional genomics datasets.

Development of the sea urchin Heliocidaris crassispina from Hong Kong is robust to ocean acidification and copper contamination

Metallic pollution is of particular concern in coastal cities. In the Asian megacity of Hong Kong, despite water qualities have improved over the past decade, some local zones are still particularly affected and could represent sinks for remobilization of labile toxic species such as copper. Ocean acidification is expected to increase the fraction of the most toxic form of copper (Cu²⁺) by 2.3-folds by 2100 (pH ≈7.7), increasing its bioavailability to marine organisms. Additionally, multiple stressors are likely to exert concomitant effects (additive, synergic or antagonist) on the organisms living in the sea. Here, we tested the hypothesis that copper-contaminated waters are more toxic to sea urchin larvae under future pH conditions. We exposed sea urchin embryos and larvae to two low-pH and two copper treatments (0.1 and 1.0 μM) in three separate experiments. Over the short time typically used for toxicity tests (up to 4-arm plutei, i.e. 3 days), larvae of the sea urchin Heliocidaris crassispina were robust and survived the copper levels present in Hong Kong waters today (≤0.19 μM) as well as the average pH projected for 2100. We, however, observed significant mortality with lowering pH in the longer, single-stressor experiment (Expt A: 8-arm plutei, i.e. 9 days). Abnormality and arm asymmetry were significantly increased by pH or/and by copper presence (depending on the experiment and copper level). Body size (d3; but not body growth rates in Expt A) was significantly reduced by both lowered pH and added copper. Larval respiration (Expt A) was doubled by a decrease at pH_T from 8.0 to 7.3 on d6. In Expt B1.0 and B0.1, larval morphology (relative arm lengths and stomach volume) were affected by at least one of the two investigated factors. Although the larvae appeared robust, these sub-lethal effects may have indirect consequences on feeding, swimming and ultimately survival. The complex relationship between pH and metal speciation/uptake is not well-characterized and further investigations are urgently needed to detangle the mechanisms involved and to identify possible caveats in routinely used toxicity tests.

Ontogenetic changes in swimming speed of silver carp, bighead carp, and grass carp larvae: implications for larval dispersal

Bighead, silver, and grass carps are invasive in the waterways of central North America, and grass carp reproduction in tributaries of the Great Lakes has now been documented. Questions about recruitment potential motivate a need for accurate models of egg and larval dispersal. Quantitative data on swimming behaviors and capabilities during early ontogeny are needed to improve these dispersal models. We measured ontogenetic changes in routine and maximum swimming speeds of bighead, grass, and silver carp larvae. Daily measurements of routine swimming speed were taken for two weeks post-hatch using a still camera and the LARVEL program, a custom image-analysis software. Larval swimming speed was calculated using larval locations in subsequent image frames and time between images. Using an endurance chamber, we determined the maximum swimming speed of larvae (post-gas bladder inflation) for four to eight weeks post-hatch. For all species, larval swimming speeds showed similar trends with respect to ontogeny: increases in maximum speed, and decreases in routine speed. Maximum speeds of bighead and grass carp larvae were similar and generally faster than silver carp larvae. Routine swimming speeds of all larvae were highest before gas bladder inflation, most likely because gas bladder inflation allowed the fish to maintain position without swimming. Downward vertical velocities of pre-gas bladder inflation fish were faster than upward velocities. Among the three species, grass carp larvae had the highest swimming speeds in the pre-gas bladder inflation period, and the lowest speeds in the post-gas bladder inflation period. Knowledge of swimming capability of these species, along with hydraulic characteristics of a river, enables further refinement of models of embryonic and larval drift.

Ocean acidification increases larval swimming speed and has limited effects on spawning and settlement of a robust fouling bryozoan, Bugula neritina

Few studies to date have investigated the effects of ocean acidification on non-reef forming marine invertebrates with non-feeding larvae. Here, we exposed adults of the bryozoan Bugula neritina and their larvae to lowered pH. We monitored spawning, larval swimming, settlement, and post-settlement individual sizes at two pHs (7.9 vs. 7.6) and settlement dynamics alone over a broader pH range (8.0 down to 6.5). Our results show that spawning was not affected by adult exposure (48h at pH7.6), larvae swam 32% faster and the newly-settled individuals grew significantly larger (5%) at pH7.6 than in the control. Although larvae required more time to settle when pH was lowered, reduced pH was not lethal, even down to pH6.5. Overall, this fouling species appeared to be robust to acidification, and yet, indirect effects such as prolonging the pelagic larval duration could increase predation risk, and might negatively impact population dynamics.

Effect of ocean acidification on growth, calcification, and gene expression in the pearl oyster, Pinctada fucata

In this study, shell growth, shell microstructure, and expression levels of shell matrix protein genes (aspein, n16, and nacrein) that play a key role in the CaCO₃ crystal polymorphism (calcite and aragonite) of the shell were investigated in the pearl oyster Pinctada fucata at pH 8.10, 7.70, and 7.40. We found that the shell length and total weight index did not vary significantly between oysters reared at pH 8.10 and 7.70, but was significantly lower at pH 7.40. Calcium content and shell hardness were not significantly different between pH 8.10 and 7.70, but were significantly different at pH 7.40. At pH 7.40, the shell exhibited a poorly organized nacreous microstructure, and showed an apparent loss of structural integrity in the nacreous layer. The prismatic layer appeared morphologically dissimilar from the samples at pH 8.10 and 7.70. The internal layer was corroded and had dissolved. At pH 7.40, the expression levels of nacrein, aspein, and n16 decreased on day 1, and remained low between days 2 and 42. The expression levels of these genes were significantly lower at pH 7.40 than at pH 8.10 and 7.70 during days 2-42. These results suggest that ocean acidification will have a limited impact on shell growth, calcification, and associated gene expression levels at a pH of 7.70, which is projected to be reached by the end of the century. The negative effects were found on calcification and gene expression occurred at the lowest experimental pH (7.40).

Ontogenetic changes in larval swimming and orientation of pre-competent sea urchin Arbacia punctulata in turbulence

Many marine organisms have complex life histories, having sessile adults and relying on the planktonic larvae for dispersal. Larvae swim and disperse in a complex fluid environment and the effect of ambient flow on larval behavior could in turn impact their survival and transport. However, to date, most studies on larvae–flow interactions have focused on competent larvae near settlement. We examined the importance of flow on early larval stages by studying how local flow and ontogeny influence swimming behavior in pre-competent larval sea urchins, Arbacia punctulata. We exposed larval urchins to grid-stirred turbulence and recorded their behavior at two stages (4- and 6-armed plutei) in three turbulence regimes. Using particle image velocimetry to quantify and subtract local flow, we tested the hypothesis that larvae respond to turbulence by increasing swimming speed, and that the increase varies with ontogeny. Swimming speed increased with turbulence for both 4- and 6-armed larvae, but their responses differed in terms of vertical swimming velocity. 4-Armed larvae swam most strongly upward in the unforced flow regime, while 6-armed larvae swam most strongly upward in weakly forced flow. Increased turbulence intensity also decreased the relative time that larvae spent in their typical upright orientation. 6-Armed larvae were tilted more frequently in turbulence compared with 4-armed larvae. This observation suggests that as larvae increase in size and add pairs of arms, they are more likely to be passively re-oriented by moving water, rather than being stabilized (by mechanisms associated with increased mass), potentially leading to differential transport. The positive relationship between swimming speed and larval orientation angle suggests that there was also an active response to tilting in turbulence. Our results highlight the importance of turbulence to planktonic larvae, not just during settlement but also in earlier stages through morphology–flow interactions.

Highlighted Article: Pre-competent, 6-armed larval urchins swim faster and are less stable in experimental turbulent flow than younger 4-armed larvae, suggesting a potential age/morphology-driven differential transport mechanism in ambient flow conditions.

Old model organisms and new behavioral end-points: Swimming alteration as an ecotoxicological response

Behavioral responses of aquatic organisms have received much less attention than developmental or reproductive ones due to the scarce presence of user-friendly tools for their acquisition. The technological development of data acquisition systems for quantifying behavior in the aquatic environment and the increase of studies on the understanding the relationship between the behavior of aquatic organisms and the physiological/ecological activities have generated renewed interest in using behavioral responses also in marine ecotoxicology. Recent reviews on freshwater environment show that behavioral end-points are comparatively fast and sensitive, and warrant further attention as tools for assessing the toxicological effects of environmental contaminants. In this mini-review, we perform a systematic analysis of the most recent works that have used marine invertebrate swimming alteration as behavioral end-point in ecotoxicological studies by assessing the differences between behavioral and acute responses in a wide range of species, in order to compare their sensitivity.

A Cryptic Marine Ciliate Feeds on Progametes of Noctiluca scintillans

The dinoflagellate Noctiluca scintillans (Noctiluca) has the ability to reproduce sexually, which may help to increase or restore its population size during periods of blooms or environmental stress. Here, we documented for the first time a marine ciliate Strombidium sp. that feeds on Noctiluca's progametes undergoing stages 5 to 9 of nuclear division. This ciliate frequently swam on or around gametogenic and some vegetative Noctiluca cells. The ciliates associated with gametogenic cells had significantly lower swimming speed and changed direction more frequently than those associated with vegetative cells, which overall increased their time spent around the food patches (progametes). This trophic interaction constitutes an upside-down predator-prey link, in which ciliates within the typical size range of Noctiluca prey, become the predators. Based on the phylogenetic tree (maximum-likelihood), there are 14 environmental clones similar to Strombidium sp. found in other coastal waters, where Noctiluca presence or blooms have been reported. This novel predator-prey relationship could therefore be common in other Noctiluca habitats. Additional studies are needed to assess the magnitude of its impacts on Noctiluca population dynamics and plankton bloom succession.

Acclimatization and Adaptive Capacity of Marine Species in a Changing Ocean

To persist in an ocean changing in temperature, pH and other stressors related to climate change, many marine species will likely need to acclimatize or adapt to avoid extinction. If marine populations possess adequate genetic variation in tolerance to climate change stressors, species might be able to adapt to environmental change. Marine climate change research is moving away from single life stage studies where individuals are directly placed into projected scenarios ('future shock' approach), to focus on the adaptive potential of populations in an ocean that will gradually change over coming decades. This review summarizes studies that consider the adaptive potential of marine invertebrates to climate change stressors and the methods that have been applied to this research, including quantitative genetics, laboratory selection studies and trans- and multigenerational experiments. Phenotypic plasticity is likely to contribute to population persistence providing time for genetic adaptation to occur. Transgenerational and epigenetic effects indicate that the environmental and physiological history of the parents can affect offspring performance. There is a need for long-term, multigenerational experiments to determine the influence of phenotypic plasticity, genetic variation and transgenerational effects on species' capacity to persist in a changing ocean. However, multigenerational studies are only practicable for short generation species. Consideration of multiple morphological and physiological traits, including changes in molecular processes (eg, DNA methylation) and long-term studies that facilitate acclimatization will be essential in making informed predictions of how the seascape and marine communities will be altered by climate change.

Swimming speed alteration in the early developmental stages of Paracentrotus lividus sea urchin as ecotoxicological endpoint

Behavioral endpoints have been used for decades to assess chemical impacts at concentrations unlikely to cause mortality. With recently developed techniques, it is possible to investigate the swimming behavior of several organisms under laboratory conditions. The aims of this study were: i) assessing for the first time the feasibility of swimming speed analysis of the early developmental stage sea urchin Paracentrotus lividus by an automatic recording system ii) investigating any Swimming Speed Alteration (SSA) on P. lividus early stages exposed to a chemical reference; iii) identifying the most suitable stage for SSA test. Results show that the swimming speed of all the developmental stages was easily recorded. The swimming speed was inhibited as a function of toxicant concentration. Pluteus were the most appropriate stage for evaluating SSA in P. lividus as ecotoxicological endpoint. Finally, swimming of sea urchin early stages represents a sensitive endpoint to be considered in ecotoxicological investigations.

Transcriptome and biomineralization responses of the pearl oyster Pinctada fucata to elevated CO2 and temperature

Ocean acidification and global warming have been shown to significantly affect the physiological performances of marine calcifiers; however, the underlying mechanisms remain poorly understood. In this study, the transcriptome and biomineralization responses of Pinctada fucata to elevated CO₂ (pH 7.8 and pH 7.5) and temperature (25 °C and 31 °C) are investigated. Increases in CO₂ and temperature induced significant changes in gene expression, alkaline phosphatase activity, net calcification rates and relative calcium content, whereas no changes are observed in the shell ultrastructure. “Ion and acid-base regulation” related genes and “amino acid metabolism” pathway respond to the elevated CO₂ (pH 7.8), suggesting that P. fucata implements a compensatory acid-base mechanism to mitigate the effects of low pH. Additionally, “anti-oxidation”-related genes and “Toll-like receptor signaling”, “arachidonic acid metabolism”, “lysosome” and “other glycan degradation” pathways exhibited responses to elevated temperature (25 °C and 31 °C), suggesting that P. fucata utilizes anti-oxidative and lysosome strategies to alleviate the effects of temperature stress. These responses are energy-consuming processes, which can lead to a decrease in biomineralization capacity. This study therefore is important for understanding the mechanisms by which pearl oysters respond to changing environments and predicting the effects of global climate change on pearl aquaculture.