Most invertebrates in the ocean begin their lives with planktonic larval phases that are critical for dispersal and distribution of these species. Larvae are particularly vulnerable to environmental change, so understanding interactive effects of environmental stressors on larval life is essential in predicting population persistence and vulnerability of species. Here, we use a novel experimental approach to rear larvae under interacting gradients of temperature, salinity, and ocean acidification, then model growth rate and duration of Olympia oyster larvae and predict the suitability of habitats for larval survival. We find that temperature and salinity are closely linked to larval growth and larval habitat suitability, but larvae are tolerant to acidification at this scale. We discover that present conditions in the Salish Sea are actually suboptimal for Olympia oyster larvae from populations in the region, and that larvae from these populations might actually benefit from some degree of global ocean change. Our models predict a vast decrease in mean pelagic larval duration by the year 2095, which has the potential to alter population dynamics for this species in future oceans. Additionally, we find that larval tolerance can explain large-scale biogeographic patterns for this species across its range.
Posts Tagged 'salinity'
Temperature and salinity, not acidification, predict near-future larval growth and larval habitat suitability of Olympia oysters in the Salish Sea
Published 19 August 2020 Science ClosedTags: biological response, growth, laboratory, modeling, mollusks, morphology, mortality, multiple factors, North Pacific, regionalmodeling, reproduction, salinity, temperature
Effects of salinity and pH of seawater on the reproduction of the sea urchin Paracentrotus lividus
Published 12 August 2020 Science ClosedTags: biological response, echinoderms, laboratory, Mediterranean, morphology, multiple factors, physiology, reproduction, salinity
Fertilization and early development are usually the most vulnerable stages in the life of marine animals, and the biological processes during this period are highly sensitive to the environment. In nature, sea urchin gametes are shed in seawater, where they undergo external fertilization and embryonic development. In a laboratory, it is possible to follow the exact morphological and biochemical changes taking place in the fertilized eggs and the developing embryos. Thus, observation of successful fertilization and the subsequent embryonic development of sea urchin eggs can be used as a convenient biosensor to assess the quality of the marine environment. In this paper, we have examined how salinity and pH changes affect the normal fertilization process and the following development of Paracentrotus lividus. The results of our studies using confocal microscopy, scanning and transmission electron microscopy, and time-lapse Ca2+ image recording indicated that both dilution and acidification of seawater have subtle but detrimental effects on many aspects of the fertilization process. They include Ca2+ signaling and coordinated actin cytoskeletal changes, leading to a significantly reduced rate of successful fertilization and, eventually, to abnormal or delayed embryonic development.
Effects of seawater salinity and pH on cellular metabolism and enzyme activities in biomineralizing tissues of marine bivalves
Published 29 June 2020 Science ClosedTags: biological response, laboratory, mollusks, multiple factors, physiology, salinity
Highlights
•Effects of salinity and pH on cellular metabolism were studied in bivalves.
•Biomineralizing cells had robust metabolism in the studied salinity and pH range.
•Oxygen consumption and protein synthesis rates declined at low pH.
•Na+/K+ ATPase activity increased at low salinity.
•H+ and Ca2+ transport activities were little affected by salinity and pH variation.
Abstract
Molluscan shell formation is a complex energy demanding process sensitive to the shifts in seawater CaCO3 saturation due to changes in salinity and pH. We studied the effects of salinity and pH on energy demand and enzyme activities of biomineralizing cells of the Pacific oyster (Crassostrea gigas) and the hard-shell clam (Mercenaria mercenaria). Adult animals were exposed for 14 days to high (30), intermediate (18), or low (10) salinity at either high (8.0-8.2) or low (7.8) pH. Basal metabolic cost as well as the energy cost of the biomineralization-related cellular processes were determined in isolated mantle edge cells and hemocytes. The total metabolic rates were similar in the hemocytes of the two studied species, but considerably higher in the mantle cells of C. gigas compared with those of M. mercenaria. Cellular respiration was unaffected by salinity in the clams’ cells, while in oysters’ cells the highest respiration rate was observed at intermediate salinity (18). In both studied species, low pH suppressed cellular respiration. Low pH led to an upregulation of Na+/K+ ATPase activity in biomineralizing cells of oysters and clams. Activities of Ca2+ ATPase and H+ ATPase, as well as the cellular energy costs of Ca2+ and H+ transport in the biomineralizing cells were insensitive to the variation in salinity and pH in the clams and oysters. Species-specific variability in cellular response to low salinity and pH indicates that the disturbance of shell formation under these conditions has different underlying mechanisms in the two studied species.
Continue reading ‘Effects of seawater salinity and pH on cellular metabolism and enzyme activities in biomineralizing tissues of marine bivalves’The combined effects of salinity and pH on shell biomineralization of the edible mussel Mytilus chilensis
Published 16 April 2020 Science ClosedTags: biological response, laboratory, mollusks, morphology, multiple factors, physiology, salinity, South Pacific
Highlights
• Coastal habitats such as estuaries show high environmental variability.
• pH and salinity impact on the periostracum organic composition.
• pH and salinity impact on the shell mineral organization.
• Salinity modulates the impact of pH on shell weight.
• The level of plasticity in shell properties differs with time exposure.
Abstract
Coastal ecosystems influenced by river discharges are subjected to important environmental changes. Understanding how marine biota cope with its environment is relevant in predicting the responses to future conditions imposed by climate change. To date, a large number of studies have addressed the role of pH on shell and biomineralization properties on multiple calcifying species; however the role of salinity in combination with other stressors has been poorly studied. In particular, the edible mussel Mytilus chilensis, an important marine resource of the Chilean coasts, inhabits estuarine areas which show high natural variability in terms of pH and salinity. Here, we studied how M. chilensis shell periostracum, shell organic matrix and crystal orientation are affected by different pH (8.1 and 7.7) and salinity conditions (30, 25 and 20 psu), isolated and in combination, at different time intervals. Our results show differences in the plasticity of the different biomineralogical properties studied during the experiment under the different pH and salinity treatments. While the periostracum thickness and the total shell organic matter were not affected by pH and salinity, the periostracum organic composition did. Higher amounts of polysaccharides were observed under low pH conditions after 20 days of experiment, while after 60 days, low salinity was responsible for the decrease of the polysaccharides and proteins in the periostracum. Low salinity also produced a major disorder in crystal organization at the outer shell surface. Finally, total shell weight was only affected by low pH conditions under lower salinity conditions (20 psu). From the results, in the majority of the shell properties observed we did not observe any combined effect of pH and salinity. Also, we detected that the magnitude of the impacts of salinity and pH are variable and time-dependent. This would be suggesting some level of acclimatization of M. chilensis to lower pH and salinity conditions.
Effects of multiple stressors on the development and performance of decapod crustaceans
Published 14 April 2020 Science ClosedTags: biological response, crustaceans, laboratory, mortality, multiple factors, nutrients, performance, reproduction, salinity, temperature
Many marine crustacean larvae develop in a relatively stable pelagic environment; therefore, they are likely to be sensitive to perturbations in their surrounding environmental conditions. Ocean Acidification (OA) is occurring on a globalised scale and may cause disruptions to crustacean larval survival. However, species and/or life history stages are not expected to respond uniformly to these near-future predicted changes. The performance of species that lack a compensatory capacity to cope with the changing conditions may potentially be detrimentally affected, which in turn may impact recruitment. In addition to this, little information exists surrounding the impacts of ocean acidification in conjunction with additional environmental stressors, such as salinity, temperature and food availability, which are predicted to covary with OA, upon brachyuran crustacean larvae. This research focused on the effects of elevated CO2, in combination with other environmental stressors, upon rates of larval development, performance and survival of a brachyuran crustacean species common to Europe (Carcinus maenas) and two species of shrimp (Palaemon serratus and Palaemon varians). These species have varying physiological abilities to cope with salinity change and such attributes may influence their capacities to survive elevated CO2 in combination with other environmental changes. Exposure of early larval stages to combinations of salinity, temperature and food limitation in C. maenas revealed that high temperature ameliorated the effect of low salinity on survival and developmental duration. Limited access to food also affected developmental duration, but exposure to elevated CO2 alone in a second experiment only affected survival, and low salinity alone had no effect. Exposure of early juvenile stages of C. maenas to CO2 and salinity, revealed that developmental duration was significantly affected by elevated CO2 and/or salinity at varying levels, whereas, for survival, such influences were only observed in later juvenile stages. These results suggest the possibility of a physiologically sensitive bottleneck within the life cycle of C. maenas. Exposure of early larval stages of the estuarine species, P. varians, to CO2 and salinity had no effect on either survival or developmental duration. For the predominantly coastal species, P. serratus, developmental duration was negatively influenced by the interaction of elevated CO2 and low salinity, but there was limited observed effect on overall survival at the early stages studied. Overall, evaluations of the effects of climate driven variables on physiological performance demonstrated that differences can occur among broods. In future, further studies are required to incorporate seasonal (and possibly spatial) variability in responses, due to maternal effects or phenotypic variation, as conclusions based on individuals collected over a short time frame are unlikely to fully represent population level responses.
pH and other upwelling hydrographic drivers in regulating copepod reproduction during the 2015 El Niño event: a follow-up study
Published 26 February 2020 Science ClosedTags: biological response, chemistry, field, laboratory, morphology, multiple factors, phytoplankton, reproduction, salinity, South Pacific
Highlights
• High salinity El Niño 2015 overlaid continuous low pH values observed in the upwelling site.
• Environmental pH-salinity and phenological regulation were detected in copepod reproduction.
• Upwelling pH-variations and high salinity El Niño events can underpin plankton responses to climate change.
Abstract
The combined upwelling-El Niño (EN) event regulation of the numerically dominant Acartia tonsa (Crustacea, Copepoda) reproduction was examined in a year-round upwelling system (23°S) of the Humboldt Eastern Boundary Upwelling System (EBUS) during the EN 2015. A previous analysis of the environmental regulation of this system is extended here by considering complementary oceanographic information (sea level, stratification indexes) and additional reproductive traits, such as maximum (MaxEPR), median (MedianEPR) and prevalence of egg producing females over a period of six months. Furthermore, field minimum-maximum pH levels were reproduced in three 96-h incubation experiments conducted under variable salinity conditions to evaluate copepod mean EPR, egg size and hatching success. Supporting previous assertions, the warm-high salinity EN 2015 was observed in the study site separately from hydrographic conditions associated with upwelling to non-upwelling regimes. Analysis of similarity-distance (Distance based Linear Model (DistLM)) and normalized data (separate-slope comparison under a General Linear Model (GLM)) showed that reproductive traits were regulated by specific combinations of ambient conditions, and that this regulation was also sensitive to the prevailing hydrographic regime. Thus, upwelling to non-upwelling transitions changing the pH, and EN-associated salinity and stratification shifts, were significantly and strongly linked to almost all reproductive traits (DistLM). Slope comparison (GLM) indicated MaxEPR and MedianEPR variations also underlie the phenology, highlighting the relationship between pH and salinity with biological variations. In conjunction with experimental observations, the current study consistently suggests that pH-variations in the upwelling realm, and EN hydrographic perturbations might underpin responses of plankton populations to climate change in productive EBUS.
Impacts of temperature, CO2, and salinity on phytoplankton community composition in the western Arctic Ocean
Published 31 January 2020 Science ClosedTags: abundance, Arctic, biological response, community composition, field, growth, laboratory, morphology, multiple factors, otherprocess, phytoplankton, salinity, temperature
The Arctic Ocean has been experiencing rapid warming, which accelerates sea ice melt. Further, the increasing area and duration of sea ice-free conditions enhance ocean uptake of CO2. We conducted two shipboard experiments in September 2015 and 2016 to examine the effects of temperature, CO2, and salinity on phytoplankton dynamics to better understand the impacts of rapid environmental changes on the Arctic ecosystem. Two temperature conditions (control: <3 and 5°C above the control), two CO2 levels (control: ∼300 and 300/450 μatm above the control; i.e., 600/750 μatm), and two salinity conditions (control: 29 in 2015 and 27 in 2016, and 1.4 below the control) conditions were fully factorially manipulated in eight treatments. Higher temperatures enhanced almost all phytoplankton traits in both experiments in terms of chl-a, accessory pigments and diatom biomass. The diatom diversity index decreased due to the replacement of chain-forming Thalassiosira spp. by solitary Cylindrotheca closterium or Pseudo-nitzschia spp. under higher temperature and lower salinity in combination. Higher CO2 levels significantly increased the growth of small-sized phytoplankton (<10 μm) in both years. Decreased salinity had marginal effects but significantly increased the growth of small-sized phytoplankton under higher CO2 levels in terms of chl-a in 2015. Our results suggest that the smaller phytoplankton tend to dominate in the shelf edge region of the Chukchi Sea in the western Arctic Ocean under multiple environmental perturbations.
Analysis of effects of environmental fluctuations on the marine mysid Neomysis awatschensis and its development as an experimental model animal
Published 26 December 2019 Science ClosedTags: biological response, crustaceans, laboratory, morphology, mortality, multiple factors, physiology, reproduction, salinity, temperature
Highlights
• Investigation of optimized culture conditions in temperature, salinity, and pH for mysid mass-culture and development as a laboratory model
• Identification of strong correlations between growth parameter and 20E level in environmental fluctuations
• Measurement of maternal effects of environmental fluctuations on second generation
Abstract
Mysids are experimental models and are among the most important food items for animals in aquaria and that support fisheries, and even for humans, but information on their performance in controlled culture systems is still limited. We reared the marine mysid Neomysis awatschensis in a controlled laboratory system, and measured its growth, 20–hydroxyecdysone (20E) levels, molting, and survival in response to environmental fluctuations in temperature, pH, and salinity, and inferred their potential associations based on annual field sampling. The 20E levels were significantly elevated during the postnauplioid stages, and even higher levels of 20E were maintained in the adult stages than in the nauplioid stages. Values of growth parameters (i.e. total length and the lengths of the antennal scale, expod, endopod, and telson) and 20E levels were higher during a 40-day period at 25 °C than at other temperatures, with shorter intermolt intervals, although morality was also increased. Among the surviving mysids, the number of newly hatched juveniles produced was higher for females exposed to 20 °C than that in other groups. Relatively higher growth and survival rates were measured at salinities over 25 practical salinity, while lower salinities under 15 practical salinity significantly reduced growth and survival. The number of newly hatched juveniles was lower at salinities under 15 practical salinity compared to those over 20 practical salinity. Overall, low temperature and salinity reduced mysid reproduction and the maintenance of the second generation. In the case of pH variation (pH of 7.0–8.0), there were no significant effects on growth and the number of newly hatched juveniles, although the survival rate was slightly lower and the 20E level fluctuated at a pH of 7.0. We believe that these associations between growth and environmental conditions can provide crucial information for optimizing mass mysid culture for experimental and ecotoxicological usage in the laboratory.
Ocean freshening and acidification differentially influences mortality and behavior of the Antarctic amphipod Gondogeneia antarctica
Published 3 December 2019 Science ClosedTags: Antarctic, biological response, crustaceans, laboratory, mortality, multiple factors, performance, salinity, zooplankton
Highlights
• Glacier retreat induced by global warming can decrease pH and salinity of the Antarctic ocean.
• The Antarctic amphipod Gondogeneia antarctica was exposed to low pH (7.6) and low salinity (27 psμ) conditions.
• Low pH increased mortality, impaired food detection, reduced shelter-use during daytime. .
• Low salinity increased cannibalism and induced abnormal swimming.
• Ocean acidification and freshening act as independent stressors influencing behavior and physiology of Antarctic amphipods.
Abstract
The Western Antarctic Peninsula (WAP) has experienced rapid atmospheric and ocean warming over the past few decades and many marine-terminating glaciers have considerably retreated. Glacial retreat is accompanied by fresh meltwater intrusion, which may result in the freshening and acidification of coastal waters. Marian Cove (MC), on King George Island in the WAP, undergoes one of the highest rates of glacial retreat. Intertidal and shallow subtidal waters are likely more susceptible to these processes, and sensitive biological responses are expected from the organisms inhabiting this area. The gammarid amphipod Gondogeneia antarctica is one of the most abundant species in the shallow, nearshore Antarctic waters, and it occupies an essential ecological niche in the coastal marine WAP ecosystem. In this study, we tested the sensitivity of G. antarctica to lowered salinity and pH by meltwater intrusion following glacial retreat. We exposed G. antarctica to four different treatments combining two salinities (34 and 27 psμ) and pH (8.0 and 7.6) levels for 26 days. Mortality, excluding cannibalized individuals, increased under low pH but decreased under low salinity conditions. Meanwhile, low salinity increased cannibalism, whereas low pH reduced food detection. Shelter use during the daytime decreased under each low salinity and pH condition, indicating that the two stressors act as disruptors of amphipod behavior. Under low salinity conditions, swimming increased during the daytime but decreased at night. Although interactions between low salinity and low pH were not observed during the experiment, the results suggest that each stressor, likely induced by glacial melting, causes altered behaviors in amphipods. These environmental factors may threaten population persistence in Marian Cove and possibly other similar glacial embayments.
Elevated carbon dioxide and reduced salinity enhance mangrove seedling establishment in an artificial saltmarsh community
Published 29 November 2019 Science ClosedTags: biological response, field, laboratory, mesocosms, morphology, multiple factors, salinity, South Pacific
The global phenomenon of mangrove encroachment into saltmarshes has been observed across five continents. It has been proposed that this encroachment is driven in part by rising atmospheric CO2 concentration and reduced salinity in saltmarshes resulting from rising sea levels enhancing the establishment success of mangrove seedlings. However, this theory is yet to be empirically tested at the community-level. In this study, we examined the effect of CO2 and salinity on seedling growth of two mangrove species, Aegiceras corniculatum and Avicennia marina, grown individually and in a model saltmarsh community in a glasshouse experiment. We found that the shoot (210%) and root (91%) biomass of the saltmarsh species was significantly greater under elevated CO2. As a result, both mangrove species experienced a stronger competitive effect from the saltmarsh species under elevated CO2. Nevertheless, A. marina seedlings produced on average 48% more biomass under elevated CO2 when grown in competition with the saltmarsh species. The seedlings tended to allocate this additional biomass to growing taller suggesting they were light limited. In contrast, A. corniculatum growth did not significantly differ between CO2 treatments. However, it had on average 36% greater growth under seawater salinity compared to hypersaline conditions. Avicennia marina seedlings were not affected by salinity. From these results, we suggest that although CO2 and salinity are not universal drivers determining saltmarsh–mangrove boundaries, it is likely that rising atmospheric CO2 concentration and reduced salinity associated with sea level rise will enhance the establishment success of mangrove seedlings in saltmarshes, which may facilitate mangrove encroachment in the future.
Reduced pH and elevated salinities affect the physiology of intertidal crab Minuca mordax (Crustacea, Decapoda)
Published 14 November 2019 Science ClosedTags: biological response, crustaceans, laboratory, mortality, multiple factors, physiology, salinity, South Atlantic
Minuca mordax is a model for studies on ocean acidification and sea-level rise because lives in mangroves and riverbanks with low pH. We investigated the physiology of the crabs exposed to differents pH (6.5 and 5.8) and salinity (25, 30, 35, 40 45S). There was not mortality or alterations in the hypo-osmoregulation, suggesting that the factors did not affect salt absorption/secretion. Reduced pH changed metabolism, ammonia excretion, and hepatosomatic index in relation to the animals kept in control pH. At elevated salinities, metabolism increased when animals were kept in control pH, but it decreased when they were exposed to acidified pH. energy substrate, varied between proteins to a mixture of proteins and lipids. Important physiological parameters, related to the catabolism of amino acids and to the energy demand are changed and the consequences might include alterations in growth and reproduction due to the energy channeling to limiting processes of homeostasis.
Anthropogenic impacts on mangrove and saltmarsh communities in eastern Australia
Published 20 August 2019 Science ClosedTags: biological response, mesocosms, morphology, multiple factors, phanerogams, salinity, South Pacific
The global phenomenon of mangrove encroachment into saltmarshes has been observed across five continents. It has been proposed that this encroachment is driven in part by rising atmospheric CO2 concentration and reduced salinity in saltmarshes resulting from rising sea levels enhancing the establishment success of mangrove seedlings. However, this is yet to be empirically tested at the community-level. In this study, we examined the effect of CO2 and salinity on seedling growth of two mangrove species, Aegiceras corniculatum and Avicennia
marina, grown individually and in a model saltmarsh community in a glasshouse experiment. We found that the shoot (210%) and root (91%) biomass of the saltmarsh species was significantly greater under elevated CO2. As a result, both mangrove species experienced a stronger competitive effect from the saltmarsh species under elevated CO2. Nevertheless, A. marina seedlings produced on average 48% more biomass under elevated CO2 when grown in competition with the saltmarsh species which they used to grow taller suggesting they were light
limited. In contrast, A. corniculatum growth did not significantly differ between CO2 treatments. However, it had on average 36% greater growth under seawater salinity compared to hypersaline conditions. Avicenna marina seedlings were not affected by salinity. From these results, we suggest that although CO2 and salinity are not universal drivers determining saltmarsh-mangrove boundaries, it is likely that rising atmospheric CO2 concentration and reduced salinity associated with sea level rise will enhance the establishment success of mangrove seedlings in saltmarshes, which may facilitate mangrove encroachment in the future.
Continue reading ‘Anthropogenic impacts on mangrove and saltmarsh communities in eastern Australia’
Hsp70 knockdown reduced the tolerance of Litopenaeus vannamei post larvae to low pH and salinity
Published 5 August 2019 Science ClosedTags: biological response, crustaceans, laboratory, molecular biology, mortality, multiple factors, reproduction, salinity
Highlights
• Injection of the white-leg shrimp with Hsp70 dsRNA eliminated Hsp70 mRNA and protein in post-larvae but had no apparent effect on survival.
• However, the survival of post larvae lacking Hsp70, as compared to those containing the heat shock protein, was reduced more than two-fold 48 h after exposure to low salinity and pH, strongly indicating that Hsp70 is required for protection against these abiotic stressors.
• This is the first time to our knowledge that RNAi has been used to demonstrate a role for Hsp70 in protecting P. vannamei post larvae against salinity and pH stress, an effect undoubtedly due to the importance Hsp70 assumes in maintaining protein homeostasis within cells.
Abstract
To better understand stress tolerance of the White leg shrimp, Litopenaeus vannamei, RNA interference (RNAi) was used to assess the role of the molecular chaperone, Hsp70 in protecting post larvae against low pH and salinity. As revealed by SDS-polyacrylamide gel electrophoresis and immunoprobing of western blots, injection of L. vannamei post larvae with Hsp70 and Hsc70 dsRNA reduced Hsp70 but had no apparent effect on survival. However, the survival of post larvae lacking Hsp70, as compared to those containing the heat shock protein, was reduced more than two-fold 48 h after exposure to low salinity and pH, strongly indicating that Hsp70 is required for protection against these abiotic stressors. This is the first time to our knowledge that RNAi has been used to demonstrate a role for Hsp70 in protecting L. vannamei post larvae against salinity and pH stress, an effect undoubtedly due to the importance Hsp70 assumes in maintaining protein homeostasis within cells. Information generated in this work provides further understanding of Hsp70 function in the stress response of Penaeid shrimp and will assist in the development of strategies to mitigate abiotic stresses experienced by aquatic invertebrates during aquaculture.
Future CO2-induced ocean acidification enhances resilience of a green tide alga to low-salinity stress
Published 16 July 2019 Science ClosedTags: algae, biological response, growth, laboratory, mortality, multiple factors, photosynthesis, physiology, salinity
To understand how Ulva species might respond to salinity stress during future ocean acidification we cultured a green tide alga Ulva linza at various salinities (control salinity, 30 PSU; medium salinity, 20 PSU; low salinity, 10 PSU) and CO2 concentrations (400 and 1000 ppmv) for over 30 days. The results showed that, under the low salinity conditions, the thalli could not complete its whole life cycle. The specific growth rate (SGR) of juvenile thalli decreased significantly with reduced salinity but increased with a rise in CO2. Compared to the control, medium salinity also decreased the SGR of adult thalli at low CO2 but did not affect it at high CO2. Similar patterns were also found in relative electron transport rate (rETR), non-photochemical quenching, saturating irradiance, and Chl b content. Although medium salinity reduced net photosynthetic rate and maximum rETR at each CO2 level, these negative effects were significantly alleviated at high CO2 levels. In addition, nitrate reductase activity was reduced by medium salinity but enhanced by high CO2. These findings indicate that future ocean acidification would enhance U. linza’s tolerance to low salinity stress and may thus facilitate the occurrence of green tides dominated by U. linza.
An ecotoxicological study on physiological responses of Archaster typicus to salinity, thermal and ocean acidification stressors
Published 8 July 2019 Science ClosedTags: biological response, echinoderms, Indian, laboratory, mortality, multiple factors, North Pacific, performance, physiology, salinity, temperature
Environmental biomarkers, also known as early warning signals, have increasingly
become a subject of interest in environmental studies. The common sea star, Archaster typicus, found in shallow sandy habitats associated with coral reefs in Singapore, was utilised to study the effects of varying treatment conditions of salinity, temperature and pH. Treatment conditions were derived from predicted future scenarios of thermal and ocean acidification conditions. Experiments were conducted to determine physiological responses of sea stars that were subjected to treatments over 24h (acute) and 120h (chronic) exposures. The biomarker responses examined included righting behaviour (time taken to right after being overturned), burrowing time and feeding responses (time
taken to close stomach/mouth plate) in experimental sea stars. To validate results of physiological biomarkers, two other biomarker responses were measured from coelomic fluid extracted from the experimental sea stars. These were the cellular lysosome integrity response (Neutral Red Retention time, NRRT) and the biochemical Ferric Reducing Antioxidant Power (FRAP) assay. In acute exposure experiments, results indicated that sea stars exhibited significant differences in physiological responses under various salinity, temperature and pH treatments. At chronic exposure regimes, lethal effects were more evident, with higher mortality rates observed in all salinity and temperature treatment regimes. Results from salinity treatments showed that physiological responses in sea stars were significantly impaired at treatments of 15‰ and 50‰ salinities. Significant results were observed in NRRT and burrowing behavioural assays in temperature treatments. Treatments with pH of 7.4 and 7.2 at the acute exposure duration resulted in a significant impairment of righting ability. The acute and chronic effects of salinity fluctuations, ocean warming and acidification on A
2 typicus were most consistently observed in the righting and burrowing behaviour assays. This indication of reduced fitness together with reduced cellular responses show a reduction in survival ability in the sea star under low salinity, high temperature and low pH conditions. Further studies could thus help us understand the effects of global warming on the physiology of organisms in various shallow water habitats.
Sperm motility of oysters from distinct populations differs in response to ocean acidification and freshening
Published 3 June 2019 Science ClosedTags: biological response, laboratory, mollusks, multiple factors, performance, reproduction, salinity
Species’ responses to climate change will reflect variability in the effects of physiological selection that future conditions impose. Here, we considered the effects of ocean acidification (increases in pCO2; 606, 925, 1250 µatm) and freshening (reductions in salinity; 33, 23, 13 PSU) on sperm motility in oysters (Crassostrea gigas) from two populations (one recently invaded, one established for 60+ years). Freshening reduced sperm motility in the established population, but this was offset by a positive effect of acidification. Freshening also reduced sperm motility in the recently invaded population, but acidification had no effect. Response direction, strength, and variance differed among individuals within each population. For the established population, freshening increased variance in sperm motility, and exposure to both acidification and freshening modified the performance rank of males (i.e. rank motility of sperm). In contrast, for the recently invaded population, freshening caused a smaller change in variance, and male performance rank was broadly consistent across treatments. That inter-population differences in response may be related to environmental history (recently invaded, or established), indicates this could influence scope for selection and adaptation. These results highlight the need to consider variation within and among population responses to forecast effects of multiple environmental change drivers.
Physiological trade-offs, acid-base balance and ion-osmoregulatory plasticity in European sea bass (Dicentrarchus labrax) juveniles under complex scenarios of salinity variation, ocean acidification and high ammonia challenge
Published 7 May 2019 Science ClosedTags: biological response, fish, laboratory, multiple factors, nutrients, physiology, salinity
Highlights
• Ocean acidification (OA) is becoming a serious threat to the marine ecosystem.
• OA can co-occur with other perturbations including salinity reduction and high ammonia.
• Interactive effects of these three stressers were evaluated on performance of European sea bass.
• Physiological, ion-osmoregulatory and gene-expression responses were modulated differentially under experimental conditions.
• Fish became more vulnerable to OA and ammonia toxicity at low salinities.
Abstract
In this era of global climate change, ocean acidification is becoming a serious threat to the marine ecosystem. Despite this, it remains almost unknown how fish will respond to the co-occurrence of ocean acidification with other conventional environmental perturbations typically salinity fluctuation and high ammonia threat. Therefore, the present work evaluated the interactive effects of elevated pCO2, salinity reduction and high environmental ammonia (HEA) on the ecophysiological performance of European sea bass (Dicentrarchus labrax). Fish were progressively acclimated to seawater (32 ppt), to brackish water (10 ppt) and to hyposaline water (2.5 ppt). Following acclimation to different salinities for at least two weeks, fish were exposed to CO2-induced water acidification representing present-day (control pCO2, 400 μatm, LoCO2) and future (high pCO2, 1000 μatm, HiCO2) sea-surface CO2 level for 3, 7 and 21 days. At the end of each exposure period, fish were challenged with HEA for 6 h (1.18 mM representing 50% of 96 h LC50). Results show that, in response to the individual HiCO2 exposure, fish within each salinity compensated for blood acidosis. Fish subjected to HiCO2 were able to maintain ammonia excretion rate (Jamm) within control levels, suggesting that HiCO2 exposure alone had no impact on Jamm at any of the salinities. For 32 and 10 ppt fish, up-regulated expression of Na+/K+-ATPase was evident in all exposure groups (HEA, HiCO2 and HEA/HiCO2 co-exposed), whereas Na+/K+/2Cl− co-transporter was up-regulated mainly in HiCO2 group. Plasma glucose and lactate content were augmented in all exposure conditions for all salinity regimes. During HEA and HEA/HiCO2, Jamm was inhibited at different time points for all salinities, which resulted in a significant build-up of ammonia in plasma and muscle. Branchial expressions of Rhesus glycoproteins (Rhcg isoforms and Rhbg) were upregulated in response to HiCO2 as well as HEA at 10 ppt, with a more moderate response in 32 ppt groups. Overall, our findings denote that the adverse effect of single exposures of ocean acidification or HEA is exacerbated when present together, and suggests that fish are more vulnerable to these environmental threats at low salinities.
Toxic algae silence physiological responses to multiple climate drivers in a tropical marine food chain
Published 24 April 2019 Science ClosedTags: communitymodeling, modeling, mollusks, multiple factors, physiology, phytoplankton, salinity, temperature
Research on the effects of climate change in the marine environment continues to accelerate, yet we know little about the effects of multiple climate drivers in more complex, ecologically relevant settings – especially in sub-tropical and tropical systems. In marine ecosystems, climate change (warming and freshening from land run-off) will increase water column stratification which is favorable for toxin producing dinoflagellates. This can increase the prevalence of toxic microalgal species, leading to bioaccumulation of toxins by filter feeders, such as bivalves, with resultant negative impacts on physiological performance. In this study we manipulated multiple climate drivers (warming, freshening, and acidification), and the availability of toxic microalgae, to determine their impact on the physiological health, and toxin load of the tropical filter-feeding clam, Meretrix meretrix. Using a structural equation modeling (SEM) approach, we found that exposure to projected marine climates resulted in direct negative effects on metabolic and immunological function and, that these effects were often more pronounced in clams exposed to multiple, rather than single climate drivers. Furthermore, our study showed that these physiological responses were modified by indirect effects mediated through the food chain. Specifically, we found that when bivalves were fed with a toxin-producing dinoflagellate (Alexandrium minutum) the physiological responses, and toxin load changed differently and in a non-predictable way compared to clams exposed to projected marine climates only. Specifically, oxygen consumption data revealed that these clams did not respond physiologically to climate warming or the combined effects of warming, freshening and acidification. Our results highlight the importance of quantifying both direct and, indirect food chain effects of climate drivers on a key tropical food species, and have important implications for shellfish production and food safety in tropical regions.
Changes in temperature, pH, and salinity affect the sheltering responses of Caribbean spiny lobsters to chemosensory cues
Published 18 March 2019 Science ClosedTags: biological response, crustaceans, laboratory, multiple factors, North Atlantic, performance, salinity, temperature
Florida Bay is home to a network of shallow mud-banks which act as barriers to circulation creating small basins that are often subject to extremes in temperature and salinity. Florida bay is also important juvenile habitat for the Caribbean spiny lobster Panulirus argus. While our understanding of the effect of environmental changes on the survival, growth, and movement of spiny lobsters is growing, the effect on their chemosensory abilities has not yet been investigated. Lobsters rely heavily on chemical cues for many biological and ecological activities, and here we report on the effect of extreme environmental events in temperature (32 °C), salinity (45ppt), and pH (7.65 pH) on social behavior and sheltering preference in P. argus. Under normal conditions, chemical cues from conspecifics are used by spiny lobsters to identify suitable shelter and cues from stone crabs and diseased individuals are used to determine shelters to be avoided. In all altered conditions, lobsters lost the ability to aggregate with conspecifics and avoid stone crabs and diseased conspecifics. Thus, seasonal extreme events, and potentially future climate change conditions, alter the chemosensory-driven behavior of P. argus and may result in decreased survivorship due to impaired shelter selection or other behaviors.
Hyposalinity tolerance inthecoccolithophorid Emiliania huxleyi under the influence of ocean acidification involves enhanced photosynthetic performance
Published 18 February 2019 Science ClosedTags: biological response, calcification, growth, laboratory, morphology, multiple factors, photosynthesis, phytoplankton, salinity
While seawater acidification induced by elevated CO2 is known to impact coccolithophores, the effects in combination with decreased salinity caused by sea ice melting and/or hydrological events have not been documented. Here we show the combined effects of seawater acidification and reduced salinity on growth, photosynthesis and calcification of Emiliania huxleyi grown at 2 CO2 concentrations (low CO2 LC: 400 μatm; high CO2 HC: 1000 μatm) and 3 levels of salinity (25, 30 and 35 ‰). A decrease of salinity from 35 to 25‰ increased growth rate, cell size and effective photochemical efficiency under both LC or HC. Calcification rates were relatively insensitive to combined effects of salinity and OA treatment but were highest under 3 5‰ and HC conditions, with higher ratios of calcification to photosynthesis (C : P) in the cells grown under 35 ‰ compared with those grown at 25 ‰. In addition, elevated dissolved inorganic carbon (DIC) concentration at the salinity of 35 ‰ stimulated its calcification. In contrast, photosynthetic carbon fixation increased almost linearly with decreasing salinity, regardless of the pCO2 treatments. When subjected to short-term exposure to high light, the low-salinity-grown cells showed the highest photochemical effective quantum yield with the highest repair rate, though HC treatment enhanced PSII damage rate. Our results suggest Emiliania huxleyi can tolerate low salinity plus acidification conditions by up-regulating its photosynthetic performance together with a relatively insensitive calcification response, which may help it better adapt to future ocean global environmental changes, especially in the coastal areas of high latitudes.
