The larvae of congeneric gastropods showed differential responses to the combined effects of ocean acidification, temperature and salinity

A comprehensive review of the effects of salinity, dissolved organic carbon, pH, and temperature on copper biotoxicity: Implications for setting the copper marine water quality criteria

In recent years, there has been a growing concern about the ecological hazards associated with copper, which has sparked increased interest in copper water quality criteria (WQC). The crucial factors affecting the bioavailability of copper in seawater are now acknowledged to be salinity, dissolved organic carbon (DOC), pH, and temperature. Research on the influence of these four water quality parameters on copper toxicity is rapidly expanding. However, a comprehensive and clear understanding of the relevant mechanisms is currently lacking, hindering the development of a consistent international method to establish the seawater WQC value for copper. As a response to this knowledge gap, this study presents a comprehensive summary with two key focuses: (1) It meticulously analyzes the effects of salinity, DOC, pH, and temperature on copper toxicity to marine organisms. It takes into account the adaptability of different species to salinity, pH and temperature. (2) Additionally, the study delves into the impact of these four water parameters on the acute toxicity values of copper on marine organisms while also reviewing the methods used in establishing the marine WQC value of copper. The study proposed a two-step process: initially zoning based on the difference of salinity and DOC, followed by the establishment of Cu WQC values for different zones during various seasons, considering the impacts of water quality parameters on copper toxicity. By providing fundamental scientific insights, this research not only enhances our understanding and predictive capabilities concerning water quality parameter-dependent Cu toxicity in marine organisms but also contributes to the development of copper seawater WQC values. Ultimately, this valuable information facilitates more informed decision-making in marine water quality management efforts.

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.

Acquiring an evolutionary perspective in marine ecotoxicology to tackle emerging concerns in a rapidly changing ocean

Tens of thousands of anthropogenic chemicals and wastes enter the marine environment each year as a consequence of the ever-increasing anthropogenic activities and demographic growth of the human population, which is majorly concentrated along coastal areas. Marine ecotoxicology has had a crucial role in helping shed light on the fate of chemicals in the environment, and improving our understanding of how they can affect natural ecosystems. However, chemical contamination is not occurring in isolation, but rather against a rapidly changing environmental horizon. Most environmental studies have been focusing on short-term within-generation responses of single life stages of single species to single stressors. As a consequence, one-dimensional ecotoxicology cannot enable us to appreciate the degree and magnitude of future impacts of chemicals on marine ecosystems. Current approaches that lack an evolutionary perspective within the context of ongoing and future local and global stressors will likely lead us to under or over estimations of the impacts that chemicals will exert on marine organisms. It is therefore urgent to define whether marine organisms can acclimate, i.e. adjust their phenotypes through transgenerational plasticity, or rapidly adapt, i.e. realign the population phenotypic performances to maximize fitness, to the new chemical environment within a selective horizon defined by global changes. To foster a significant advancement in this research area, we review briefly the history of ecotoxicology, synthesis our current understanding of the fate and impact of contaminants under global changes, and critically discuss the benefits and challenges of integrative approaches toward developing an evolutionary perspective in marine ecotoxicology: particularly through a multigenerational approach. The inclusion of multigenerational studies in Ecological Risk Assessment framework (ERA) would provide significant and more accurately information to help predict the risks of pollution in a rapidly changing ocean.

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.

Vulnerability of Tritia reticulata (L.) early life stages to ocean acidification and warming

Ocean acidification and warming (OA-W) result mainly from the absorption of carbon dioxide and heat by the oceans, altering its physical and chemical properties and affecting carbonate secretion by marine calcifiers such as gastropods. These processes are ongoing, and the projections of their aggravation are not encouraging. This work assesses the concomitant effect of the predicted pH decrease and temperature rise on early life stages of the neogastropod Tritia reticulata (L.), a common scavenger of high ecological importance on coastal ecosystems of the NE Atlantic. Veligers were exposed for 14 days to 12 OA-W experimental scenarios generated by a factorial design of three pH levels (targeting 8.1, 7.8 and 7.5) at four temperatures (16, 18, 20 and 22 °C). Results reveal effects of both pH and temperature (T °C) on larval development, growth, shell integrity and survival, individually or interactively at different exposure times. All endpoints were initially driven by pH, with impaired development and high mortalities being recorded in the first week, constrained by the most acidic scenarios (pH_target 7.5). Development was also significantly driven by T °C, and its acceleration with warming was observed for the remaining exposure time. Still, by the end of this 2-weeks trial, larval performance and survival were highly affected by the interaction between pH and T °C: growth under warming was evident but only for T °C ≤ 20 °C and carbonate saturation (pH_target ≥ 7.8). In fact, carbonate undersaturation rendered critical larval mortality (100%) at 22 °C, and the occurrence of extremely vulnerable, unshelled specimens in all other tested temperatures. As recruitment cohorts are the foundation for future populations, our results point towards the extreme vulnerability of this species in case tested scenarios become effective that, according to the IPCC, are projected for the northern hemisphere, where this species is ubiquitous, by the end of the century. Increased veliger mortality associated with reduced growth rates, shell dissolution and loss under OA-W projected scenarios will reduce larval performance, jeopardizing T. reticulata subsistence.

Effects of long-term exposure to reduced pH conditions on the shell and survival of an intertidal gastropod

Volcanic CO₂ vents are useful environments for investigating the biological responses of marine organisms to changing ocean conditions (Ocean acidification, OA). Marine shelled molluscs are highly sensitive to changes in seawater carbonate chemistry. In this study, we investigated the effects of reduced pH on the intertidal gastropod, Phorcus sauciatus, in a volcanic CO₂ vent off La Palma Island (Canary Islands, North East Atlantic Ocean), a location with a natural pH gradient ranging from 7.0 to 8.2 over the tidal cycles. Density and size-frequency distribution, shell morphology, shell integrity, fracture resistance, and desiccation tolerance were evaluated between populations from control and CO₂ vent sites. We found no effects of reduced pH on population parameters or desiccation tolerance across the pH gradient, but significant differences in shell morphology, shell integrity, and fracture resistance were detected. Individuals from the CO₂ vent site exhibited a higher shell aspect ratio, greater percentages of shell dissolution and break, and compromised shell strength than those from the control site. Our results highlight that long-term exposure to high pCO₂ can negatively affect the shell features of P. sauciatus but may not have a significant effect on population performance. Moreover, we suggest that loss of shell properties could lead to changes in predator-prey interactions.

Differential sensitivity of larvae to ocean acidification in two interacting mollusc species

Anthropogenically-induced ocean acidification (OA) scenarios of decreased pH and altered carbonate chemistry are threatening the fitness of coastal species and hence near-shore ecosystems' biodiversity. Differential tolerances to OA between species at different trophic levels, for example, may alter species interactions and impact community stability. Here we evaluate the effect of OA on the larval stages of the rock oyster, Saccostrea cucullata, a dominant Indo-Pacific ecosystem engineer, and its key predator, the whelk, Reishia clavigera. pH as low as 7.4 had no significant effect on mortality, abnormality or growth of oyster larvae, whereas whelk larvae exposed to pH 7.4 experienced increased mortality (up to ∼30%), abnormalities (up to 60%) and ∼3 times higher metabolic rates compared to controls. Although these impacts' long-term consequences are yet to be investigated, greater vulnerability of whelk larvae to OA could impact predation rates on intertidal rocky shores, and have implications for subsequent community dynamics.

Will temperature and salinity changes exacerbate the effects of seawater acidification on the marine microalga Phaeodactylum tricornutum?

To evaluate the effects related to the combination of potential future changes in pH, temperature and salinity on microalgae, a laboratory experiment was performed using the marine diatom Phaeodactylum tricornutum. Populations of this species were exposed during 48h to a three-factor experimental design (3×2×2) with two artificial pH values (6, 7.4), two levels of temperature (23°C, 28°C), two levels of salinity (34psu, 40psu) and a control (pH8, Temp 23°C, Sal 34psu). The effects on growth, cell viability, metabolic activity, and inherent cell properties (size, complexity and autofluorescence) of P. tricornutum were studied using flow cytometry. The results showed adverse effects on cultures exposed to pH6 and high temperature and salinity, being the inherent cell properties the most sensitive response. Also, linked effects of these parameters resulted on cell viability and cell size decrease and an increase of cell autofluorescence. The conclusions obtained from this work are useful to address the potential effects of climate change (in terms of changes on pH, salinity and temperature) in microalgae.

Parasitic infection alters the physiological response of a marine gastropod to ocean acidification

Increased hydrogen ion concentration and decreased carbonate ion concentration in seawater are the most physiologically relevant consequences of ocean acidification (OA). Changes to either chemical species may increase the metabolic cost of physiological processes in marine organisms, and reduce the energy available for growth, reproduction and survival. Parasitic infection also increases the energetic demands experienced by marine organisms, and may reduce host tolerance to stressors associated with OA. This study assessed the combined metabolic effects of parasitic infection and OA on an intertidal gastropod,Zeacumantus subcarinatus. Oxygen consumption rates and tissue glucose content were recorded in snails infected with one of three trematode parasites, and an uninfected control group, maintained in acidified (7·6 and 7·4 pH) or unmodified (8·1 pH) seawater. Exposure to acidified seawater significantly altered the oxygen consumption rates and tissue glucose content of infected and uninfected snails, and there were clear differences in the magnitude of these changes between snails infected with different species of trematode. These results indicate that the combined effects of OA and parasitic infection significantly alter the energy requirements ofZ. subcarinatus, and that the species of the infecting parasite may play an important role in determining the tolerance of marine gastropods to OA.

Animal behaviour shapes the ecological effects of ocean acidification and warming: moving from individual to community-level responses

Biological communities are shaped by complex interactions between organisms and their environment as well as interactions with other species. Humans are rapidly changing the marine environment through increasing greenhouse gas emissions, resulting in ocean warming and acidification. The first response by animals to environmental change is predominantly through modification of their behaviour, which in turn affects species interactions and ecological processes. Yet, many climate change studies ignore animal behaviour. Furthermore, our current knowledge of how global change alters animal behaviour is mostly restricted to single species, life phases and stressors, leading to an incomplete view of how coinciding climate stressors can affect the ecological interactions that structure biological communities. Here, we first review studies on the effects of warming and acidification on the behaviour of marine animals. We demonstrate how pervasive the effects of global change are on a wide range of critical behaviours that determine the persistence of species and their success in ecological communities. We then evaluate several approaches to studying the ecological effects of warming and acidification, and identify knowledge gaps that need to be filled, to better understand how global change will affect marine populations and communities through altered animal behaviours. Our review provides a synthesis of the far-reaching consequences that behavioural changes could have for marine ecosystems in a rapidly changing environment. Without considering the pervasive effects of climate change on animal behaviour we will limit our ability to forecast the impacts of ocean change and provide insights that can aid management strategies.

Will jumping snails prevail? Influence of near-future CO2, temperature and hypoxia on respiratory performance in the tropical conch Gibberulus gibberulus gibbosus

Tropical coral reef organisms are predicted to be especially sensitive to ocean warming because many already live close to their upper thermal limit, and the expected rise in ocean CO2 is proposed to further reduce thermal tolerance. Little, however, is known about the thermal sensitivity of a diverse and abundant group of reef animals, the gastropods. The humpbacked conch (Gibberulus gibberulus gibbosus), inhabiting subtidal zones of the Great Barrier Reef, was chosen as a model because vigorous jumping, causing increased oxygen uptake (ṀO2), can be induced by exposure to odour from a predatory cone snail (Conus marmoreus). We investigated the effect of present-day ambient (417–454 µatm) and projected-future (955–987 µatm) PCO2 on resting (ṀO2,rest) and maximum (ṀO2,max) ṀO2, as well as ṀO2 during hypoxia and critical oxygen tension (PO2,crit), in snails kept at present-day ambient (28°C) or projected-future temperature (33°C). ṀO2,rest and ṀO2,max were measured both at the acclimation temperature and during an acute 5°C increase. Jumping caused a 4- to 6-fold increase in ṀO2, and ṀO2,max increased with temperature so that absolute aerobic scope was maintained even at 38°C, although factorial scope was reduced. The humpbacked conch has a high hypoxia tolerance with a PO2,crit of 2.5 kPa at 28°C and 3.5 kPa at 33°C. There was no effect of elevated CO2 on respiratory performance at any temperature. Long-term temperature records and our field measurements suggest that habitat temperature rarely exceeds 32.6°C during the summer, indicating that these snails have aerobic capacity in excess of current and future needs.

Physiological responses and scope for growth upon medium-term exposure to the combined effects of ocean acidification and temperature in a subtidal scavenger Nassarius conoidalis

Physiological responses (ingestion rate, absorption rate and efficiency, respiration, rate, excretion rate) and scope for growth of a subtidal scavenging gastropod Nassarius conoidalis under the combined effects of ocean acidification (pCO2 levels: 380, 950, 1250 μatm) and temperature (15, 30 °C) were investigated for 31 days. There was a significant reduction in all the physiological rates and scope for growth following short-term exposure (1-3 days) to elevated pCO2 except absorption efficiency at 15 °C and 30 °C, and respiration rate and excretion rate at 15 °C. The percentage change in the physiological rates ranged from 0% to 90% at 15 °C and from 0% to 73% at 30 °C when pCO2 was increased from 380 μatm to 1250 μatm. The effect of pCO2 on the physiological rates was enhanced at high temperature for ingestion, absorption, respiration and excretion. When the exposure period was extended to 31 days, the effect of pCO2 was significant on the ingestion rate only. All the physiological rates remained unchanged when temperature increased from 24 °C to 30 °C but the rates at 15 °C were significantly lower, irrespective of the duration of exposure. Our data suggested that a medium-term exposure to ocean acidification has no effect on the energetics of N. conoidalis. Nevertheless, the situation may be complicated by a longer term of exposure and/or a reduction in salinity in a warming world.

Differential tolerances to ocean acidification by parasites that share the same host

Ocean acidification is predicted to cause major changes in marine ecosystem structure and function over the next century, as species-specific tolerances to acidified seawater may alter previously stable relationships between coexisting organisms. Such differential tolerances could affect marine host-parasite associations, as either host or parasite may prove more susceptible to the stressors associated with ocean acidification. Despite their important role in many ecological processes, parasites have not been studied in the context of ocean acidification. We tested the effects of low pH seawater on the cercariae and, where possible, the metacercariae of four species of marine trematode parasite. Acidified seawater (pH 7.6 and 7.4, 12.5 °C) caused a 40-60% reduction in cercarial longevity and a 0-78% reduction in metacercarial survival. However, the reduction in longevity and survival varied distinctly between parasite taxa, indicating that the effects of reduced pH may be species-specific. These results suggest that ocean acidification has the potential to reduce the transmission success of many trematode species, decrease parasite abundance and alter the fundamental regulatory role of multi-host parasites in marine ecosystems.

Effects of low salinity on adult behavior and larval performance in the intertidal gastropod Crepipatella peruviana (Calyptraeidae)

Shallow-water coastal areas suffer frequent reductions in salinity due to heavy rains, potentially stressing the organisms found there, particularly the early stages of development (including pelagic larvae). Individual adults and newly hatched larvae of the gastropod Crepipatella peruviana were exposed to different levels of salinity stress (32(control), 25, 20 or 15), to quantify the immediate effects of exposure to low salinities on adult and larval behavior and on the physiological performance of the larvae. For adults we recorded the threshold salinity that initiates brood chamber isolation. For larvae, we measured the impact of reduced salinity on velar surface area, velum activity, swimming velocity, clearance rate (CR), oxygen consumption (OCR), and mortality (LC50); we also documented the impact of salinity discontinuities on the vertical distribution of veliger larvae in the water column. The results indicate that adults will completely isolate themselves from the external environment by clamping firmly against the substrate at salinities ≤24. Moreover, the newly hatched larvae showed increased mortality at lower salinities, while survivors showed decreased velum activity, decreased exposed velum surface area, and decreased mean swimming velocity. The clearance rates and oxygen consumption rates of stressed larvae were significantly lower than those of control individuals. Finally, salinity discontinuities affected the vertical distribution of larvae in the water column. Although adults can protect their embryos from low salinity stress until hatching, salinities <24 clearly affect survival, physiology and behavior in early larval life, which will substantially affect the fitness of the species under declining ambient salinities.