Posts Tagged 'reproduction'

Sex and gametogenesis stage are strong drivers of gene expression in Mytilus edulis exposed to environmentally relevant plasticiser levels and pH 7.7

Plastic pollution and changes in oceanic pH are both pressing environmental issues. Little emphasis, however, has been placed on the influence of sex and gametogenesis stage when investigating the effects of such stressors. Here, we examined histology and molecular biomarkers of blue mussels Mytilus edulis exposed for 7 days to a pH 7.7 scenario (− 0.4 units) in combination with environmentally relevant concentrations (0, 0.5 and 50 µg/L) of the endocrine disrupting plasticiser di-2-ethylhexyl phthalate (DEHP). Through a factorial design, we investigated the gametogenesis cycle and sex-related expression of genes involved in pH homeostasis, stress response and oestrogen receptor-like pathways after the exposure to the two environmental stressors. As expected, we found sex-related differences in the proportion of developing, mature and spawning gonads in histological sections. Male gonads also showed higher levels of the acid–base regulator CA2, but females had a higher expression of stress response-related genes (i.e. sodcathsp70). We found a significant effect of DEHP on stress response-related gene expression that was dependent on the gametogenesis stage, but there was only a trend towards downregulation of CA2 in response to pH 7.7. In addition, differences in gene expression between males and females were most pronounced in experimental conditions containing DEHP and/or acidified pH but never the control, indicating that it is important to consider sex and gametogenesis stage when studying the response of mussels to diverse stressors.

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Effect of temperature and CO2 concentration on the morphogenesis of sagittal otoliths in Atlantic herring (Clupea harengus) larvae

Otoliths are very useful biomarkers especially for fish growth. Climate change with the associated global changes in warming and acidification could affect the calcification and the shape of otoliths during the crucial larval period in teleost fish. To evaluate this predicted combined effect of temperature and CO2, Atlantic herring (Clupea harengus) embryos and larvae were reared from hatching to respectively 47 and 60 days post-hatching (dph), under present day conditions and a scenario predicted for the year 2100 (IPCC RCP8.5). Otolith morphogenesis was tracked by analyzing area and normalized Elliptical Fourier coefficients. We found that otolith area for fish of similar size increased under the predicted 2100 climate change scenario compared to the present day. Climate change does not, however, seem to directly affect the otolith shape. Finally, the onset of otolith morphogenesis is hardwired, but the relationship between otolith and fish size is environment-dependent.

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Impacts of seawater pH buffering on the larval microbiome and carry-over effects on later-life disease susceptibility in Pacific oysters

Ocean acidification upwelling events and the resulting lowered aragonite saturation state of seawater have been linked to high mortality of marine bivalve larvae in hatcheries. Major oyster seed producers along North America’s west coast have mitigated impacts via seawater pH buffering (e.g., addition of soda ash). However, little consideration has been given to whether such practice may impact the larval microbiome, with potential carry-over effects on immune competency and disease susceptibility in later-life stages. To investigate possible impacts, Pacific oysters (Crassostrea gigas) were reared under soda ash pH buffered or ambient pH seawater conditions for the first 24 h of development. Both treatment groups were then reared under ambient pH conditions for the remainder of the developmental period. Larval microbiome, immune status (via gene expression), growth, and survival were assessed throughout the developmental period. Juveniles and adults arising from the larval run were then subjected to laboratory-based disease challenges to investigate carry-over effects. Larvae reared under buffered conditions showed an altered microbiome, which was still evident in juvenile animals. Moreover, reduced survival was observed in both juveniles and adults of the buffered group under a simulated marine heatwave and Vibrio exposure compared with those reared under ambient conditions. Results suggest that soda ash pH buffering during early development may compromise later-life stages under stressor conditions, and illustrate the importance of a long-view approach with regard to hatchery husbandry practices and climate change mitigation.

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Could acidified environments intensify illicit drug effects on the reproduction of marine mussels?

The increasing oceanic uptake is a direct response to the increasing atmospheric burden of CO2. Oceans are experiencing both physical and biogeochemical changes. This increase in CO2 hosts in oceans promotes changes in pH and seawater chemistry that can modify the speciation of compounds, largely due to dependent element speciation on physicochemical parameters (salinity, pH, and redox potential). So, ocean acidification can trigger enhanced toxicity of illicit drugs to non-target marine organisms due to the combined effects of crack cocaine and low pH (from 8.3 to 7.0 pH values) on the reproduction of the marine mussel Perna perna. Fertilization rate and embryo–larval development were used as endpoints to assess the effects of crack-cocaine concentrations (6.25, 12.5, 25, 50, and 100 mg L−1) and its association with pH values variation (8.3, 8.0, 7.5, and 7.0). The IC50 was calculated from the results of an embryo–larval assay in different methods of acidification (CO2 and HCl), which evidenced that HCl treatment was more toxic than CO2 treatment for the same drug concentrations. Results showed that the gametes of P. perna react to acidification when exposed to crack-cocaine concentration and pH reductions.

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Life-history traits in the Pacific oyster Crassostrea gigas are robust to ocean acidification under two thermal regimes

Ocean acidification and warming (OAW) are pressing contemporary issues affecting marine life and specifically calcifying organisms. Here, we investigated the direct effects of OAW on life-history traits of the Pacific oyster Crassostrea gigas, the most cultivated bivalve species worldwide. We also tested whether parental conditioning history shaped the phenotypic characters of their progenies (intergenerational carryover effects). Adult oysters and their offspring were exposed to two temperatures (18°C, +3°C) under ambient pH conditions or under an end-of-century acidification scenario (−0.33 pH unit). In adults, we monitored standard biometric and reproductive parameters, stress response by quantifying neuroendocrine metabolites and gamete quality. In larvae, we measured hatching rate, size, biochemical quality, and behavior. We found that reducing pH reduced growth rate and activated the serotonin system, but increasing temperature attenuated these effects. There was no effect of pH on reproduction at either temperature, and no intergenerational carryover effects. Larval characteristics were similar between treatments, regardless of parental conditioning history. Thus, the Pacific oyster seems robust to changes in pH, and increasing temperature is not an aggravating factor. We emphasize that the use of neuroendocrine indicators holds promise for revealing sublethal impacts of environmental changes.

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Effects of acidification on fish larval abundance at Teknaf coast, Bangladesh

The study aimed to investigate the effects of acidification on fish larvae abundance at the Teknaf coast. From January 8 to December 14, 2021, samples of fish larvae were collected at every month from the Teknaf coast. From the bottom to the surface, Bongo-Net with a 500 µm mesh size was being towed. A total of 1,120 larvae were gathered from the research area during the survey. In the study region, 93 larvae/1,000 m3 were found to be the mean density of all fish larvae. The hydrological parameters such as water temperature, pH, salinity, and total alkalinity were determined to find out the effects of these variables on the larvae abundance along the Teknaf coast. The average values of the parameters including water temperature, pH, salinity, and total alkalinity were found at 28.41°C, 8.36, 23.57 PSU, and 113.25 mg/l respectively. The ocean acidification factors including pCO2, HCO3-, CO32-, DIC, ΩAragonite, and ΩCalcite were also determined by using the “seacarb” package of R programming to find out the effects of these variables on the larvae abundance along the Teknaf coast. The average values of the factors including pCO2, HCO3-, CO32-, DIC, ΩAragonite, and ΩCalcite were found 128.72 µatm, 0.000751 mole/kg, 0.000138 mole/kg, 0.000892 mole/kg, 2.3544 and 3.7028 respectively. The results showed an insignificant relationship between pCO2 and fish larvae abundance throughout the Teknaf coast. However, there was a negative correlation between pCO2 and pH. The findings of this research indicate that OA affects fish larvae abundance at Teknaf coast. Regional fisheries management organizations will be better able to make decisions about the management of the extremely valuable fish larvae as a result of future population-level predictions of the impacts of ocean acidification.

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Crustacean ecology in a changing climate

Whilst crustaceans occupy a diversity of ecological niches and have adapted to many environmental challenges, relatively little is known on how the predicted changes associated with climate change will impact individuals, communities, species and ecosystems globally. Direct oceanic change to seawater temperature, pH, alkalinity, oxygen level and salinity and indirect impacts on weather, seasonality, food availability and changes in ecological networks will put pressure upon crustaceans to acclimate. There is now emerging evidence that behaviour, physiology, fitness and ultimately reproduction and survival of coastal crustaceans is altered under experimental climate change conditions, with most studies showing negative impacts. Nevertheless measurable endpoints, multigenerational and ecosystem studies are to date extremely rare and the full impact of climate change stress upon crustaceans is nowhere near fully understood.

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Impacts of global environmental change on fish and fisheries of the Northeastern Pacific Ocean

Marine fishes’ intolerance to global change conditions can affect the abundance and distribution of ecologically and economically important species, reshape the structure of trophic webs, and profoundly impact the human communities that rely on fished species for their livelihood and culture. Only by understanding the vulnerability of fished species and fishing communities to global change can we take effective adaptive action and implement climate-ready fisheries management. In this dissertation, I investigate the vulnerability of eight commercially important fished species and one fishing community to global change in the Northeastern Pacific Ocean. In chapter one, I expose Lingcod (Ophiodon elongatus), a benthic egg layer, to temperature, oxygen, and pH conditions we expect to see in the Central California Current System (CCS) by the year 2050 and 2100. I examine both the lethal and sublethal effects of these two multistressor climate change scenarios by measuring differences in metabolic rate, hatching success, and larval quality between treatments. In chapter two, I use a species distribution modeling approach to evaluate how historical (1982-2019) and projected (2030 through end-of-century) warming in the Eastern Bering Sea (EBS), Alaska, affects predator-prey interactions for some of the most commercially valuable fisheries in the U.S. These species include: 1) Pacific Cod (Gadus macrocephalus), 2) Pacific Halibut (Hippoglossus stenolepis), 3) Arrowtooth Flounder, 4) Walleye Pollock (Gadus chalcogrammus), 5) Tanner Crab (Chionoecetes bairdi), 6) Snow Crab (Chionoecetes opilio), and 7) Alaskan Pink Shrimp (Pandalus eous). In chapter three, I use social network analyses to depict the resilience and adaptability of the California Market Squid fishery (Doryteuthis opalescens), the most valuable in the state, to climate perturbations and project changes in habitat suitability by the year 2100 in the CCS. By using all of these vulnerability assessment tools, we can begin to prepare U.S. west coast fisheries for global environmental change.

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Ocean acidification does not overlook sex: review of understudied effects and implications of low pH on marine invertebrate sexual reproduction

Sexual reproduction is a fundamental process essential for species persistence, evolution, and diversity. However, unprecedented oceanographic shifts due to climate change can impact physiological processes, with important implications for sexual reproduction. Identifying bottlenecks and vulnerable stages in reproductive cycles will enable better prediction of the organism, population, community, and global-level consequences of ocean change. This article reviews how ocean acidification impacts sexual reproductive processes in marine invertebrates and highlights current research gaps. We focus on five economically and ecologically important taxonomic groups: cnidarians, crustaceans, echinoderms, molluscs and ascidians. We discuss the spatial and temporal variability of experimental designs, identify trends of performance in acidified conditions in the context of early reproductive traits (gametogenesis, fertilization, and reproductive resource allocation), and provide a quantitative meta-analysis of the published literature to assess the effects of low pH on fertilization rates across taxa. A total of 129 published studies investigated the effects of ocean acidification on 122 species in selected taxa. The impact of ocean acidification is dependent on taxa, the specific reproductive process examined, and study location. Our meta-analysis reveals that fertilization rate decreases as pH decreases, but effects are taxa-specific. Echinoderm fertilization appears more sensitive than molluscs to pH changes, and while data are limited, fertilization in cnidarians may be the most sensitive. Studies with echinoderms and bivalve molluscs are prevalent, while crustaceans and cephalopods are among the least studied species even though they constitute some of the largest fisheries worldwide. This lack of information has important implications for commercial aquaculture, wild fisheries, and conservation and restoration of wild populations. We recommend that studies expose organisms to different ocean acidification levels during the entire gametogenic cycle, and not only during the final stages before gametes or larvae are released. We argue for increased focus on fundamental reproductive processes and associated molecular mechanisms that may be vulnerable to shifts in ocean chemistry. Our recommendations for future research will allow for a better understanding of how reproduction in invertebrates will be affected in the context of a rapidly changing environment.

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Early life stages of a Mediterranean coral are vulnerable to ocean warming and acidification (update)

The ability of coral populations to recover from disturbance depends on larval dispersion and recruitment. While ocean warming and acidification effects on adult corals are well documented, information on early life stages is comparatively scarce. Here, we investigate whether ocean warming and acidification can affect the larval and recruit development of the Mediterranean azooxanthellate coral Astroides calycularis. Larvae and recruits were raised for 9 months at ambient (23 C) and warm (26 C) temperatures and ambient (8.0) and low pH (7.7, on the total scale). The timing of the larval metamorphosis, growth of the recruit polyp by linear extension and budding, and skeletal characteristics of the 9-month-old polyps were monitored. Settlement and metamorphosis were more successful and hastened under a warm temperature. In contrast, low pH delayed the metamorphosis and affected the growth of the recruits by reducing the calcified area of attachment to the substrate as well as by diminishing the skeleton volume and the number of septa. However, skeleton density was higher under low pH and ambient temperature. The warm temperature and low-pH treatment had a negative impact on the survival, settlement, and growth of recruits. This study provides evidence of the threat represented by ocean warming and acidification for the larval recruitment and the growth of recruits of A. calycularis.

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Epigenetic plasticity enables copepods to cope with ocean acidification

Plasticity enhances species fitness and survival under climate change. Ocean acidification poses a potential threat to copepods, a major zooplankton group that serves as a key link between the lower and higher trophic levels in the marine environment, yet the mechanisms underlying different adaptive responses remain poorly understood. Here we show that although elevated CO2 can exert negative effects on reproduction of Paracyclopina nana, multigenerational plasticity can enable recovery after three generations. By integrating the methylome and transcriptome with the draft genome and undertaking DNA methylation treatments, we demonstrate the vital role of epigenetic modifications in ocean acidification responses and identify regions associated with reproductive resilience. Our results demonstrate that DNA methylation might play an important role in enhancing species fitness of copepods and that failing to consider phenotypic plasticity could lead to overestimation of species’ vulnerabilities.

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Camouflage and exploratory avoidance of newborn cuttlefish under warming and acidification

Ocean warming and acidification have been shown to elicit deleterious effects on cephalopod mollusks, especially during early ontogeny, albeit effects on behavior remain largely unexplored. This study aimed to evaluate, for the first time, the effect of end-of-the-century projected levels of ocean warming (W; + 3 °C) and acidification (A; 980 µatm pCO2) on Sepia officinalis hatchlings’ exploratory behavior and ability to camouflage in different substrate complexities (sand and black and white gravel). Cuttlefish were recorded in open field tests, from which mobility and exploratory avoidance behavior data were obtained. Latency to camouflage was registered remotely, and pixel intensity of body planes and background gravel were extracted from photographs. Hatching success was lowered under A and W combined (AW; 72.7%) compared to control conditions (C; 98.8%). Motion-related behaviors were not affected by the treatments. AW delayed camouflage response in the gravel substrate compared to W alone. Moreover, cuttlefish exhibited a higher contrast and consequently a stronger disruptive pattern under W, with no changes in background matching. These findings suggest that, although climate change may elicit relevant physiological challenges to cuttlefish, camouflage and mobility of these mollusks are not undermined under the ocean of tomorrow. 

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Phenotypic plasticity in economically and ecologically important bivalves in response to changing environments

Marine bivalves are ecologically important, providing ecosystem services like filtering water, stabilizing substrate, and creating hard structure for epibionts. Cultured bivalves are also economically important, supporting thousands of aquaculture jobs nationwide and providing valuable protein sources for our growing human population. However, recent shifts in the environment such as temperature, ocean acidification, hypoxia, and extreme environmental variation have greatly affected bivalve physiology, reproduction, and survival across multiple lifestages. Bivalves in the Northeast Pacific are increasingly vulnerable climate change related stressors like intensifying upwelling and weather extremes, defined stratification, and unique geography which causes distinct spatial and seasonal variation. I seek to investigate if higher degrees of phenotypic plasticity and parental carryover will have the potential to improve bivalve’s fitness and tolerance as climate change progresses. My goal is to evaluate plastic capacity by taking a multi-method approach to assessing the physiological metrics of several important bivalve species, using both field and laboratory experiments. Early lifestages are greatly influenced by parental environmental history leading to carryover effects, favoring phenotypes that have a higher likelihood of surviving. In addition to natural selection in the wild, commercial and restoration aquaculturists may select for beneficial phenotypes in adults and offspring which would yield the most desirable characteristics. In our experiment, I focus on three different species: the purple-hinge rock scallop Crassadoma gigantea, the Mediterranean mussels Mytilus galloprovincialis, and the Olympia oyster Ostrea lurida. By choosing a suite of native and non-native, inter- and subtidal species, I hope to obtain a broad snapshot of physiological responses to help restore vulnerable species and maximize quality of farmed product. Chapter 1 examines physiological responses of the scallop C. gigantea to climate change related stressors in the laboratory. I conducted a full factorial laboratory experiment, manipulating pCO2 and temperature to mimic current and future ocean acidification and warming levels. After six weeks of acclimation, I found that stressors reduced shell strength and periostracum (outer shell layer) density. Only acidification affected lipids, and fatty acid content varied between treatments. I was the first to quantify microbial composition of a bivalve under multiple stressors and I found differences in the microbiome, especially with temperature stress. Chapter 2 explores physiological responses of C. gigantea and M. galloprovincialis in a six-month field acclimatation experiment. Shellfish were deployed in cages in Puget Sound, Washington at either 5 or 30 m below the surface. I found that environmental gradients varied seasonally and spatially and affected growth, shell strength, and isotopic signatures. There were differences between the two species, namely with shell strength and δ13C. I found that no one depth or time period yielded the most desirable traits for culturing, and I highlight the concerning patterns in Puget Sound’s most productive region. In Chapter 3, I took my research one step further by introducing a spatial component to a one-year field experiment. I outplanted O. lurida in cages at 5 m depth in three different locations in Puget Sound, one of which also had a 20 m depth. Each of these locations had an oceanographic monitoring buoy which allowed me to couple physiological data with high-resolution environmental data. I spawned the oysters to test parental carryover and found evidence in growth rates of larvae, which when acclimated to high temperatures, mirrored their parents. Interestingly, larval survival did not coincide with growth, and through respirometry, I found that 20°C may be a bottleneck for this lifestage. Adult oyster growth, isotopic signatures, and gametogenesis were affected by both seasonal and spatial field conditions. Metabolic responses to pH and temperature depending on recent acclimatization history. This research shows evidence of strong adaptive plasticity which was demonstrated by energetic trade-offs and parental carryover. Chapter 4 acclimatized M. galloprovincialis in the field in a similar fashion to O. lurida. Growth, shell strength, and isotopes were all affected by season and site. Similar to oysters, acute metabolic rate of each site and season was affected differently between pH and temperature. Shellfish covered in Chapter 3/4 have a high degree of plasticity and results are useful to restoration (oyster) and commercial (mussel) aquaculturists to create selective breeding programs that will withstand climate change. Results of this dissertation demonstrate the rapid degree of phenotypic plasticity and capacity for parental carryover in field and laboratory setting though a wide array of physiological analysis. Outcomes of this research add to the limited but growing body of literature about multiple-stressors and field experiments, and indents to assist aquaculturists as climate change progresses.

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Responses of early life stages of European abalone (Haliotis tuberculata) to ocean acidification after parental conditioning: Insights from a transgenerational experiment

Highlights

  • Abalone has experienced severe population decline worldwide due to overfishing, disease and climate change.
  • OA effects were evaluated on reproduction and early life stages of H. tuberculata through a transgenerational experiment.
  • No carry-over effects were observed on abalone offspring following parental exposure to OA.
  • Larval and juvenile fitness were affected by a pH decrease of 0.3 unit.
  • Species dispersion and survival may be compromised in the near future, with potential negative consequences for European abalone populations.

Abstract

CO2 absorption is leading to ocean acidification (OA), which is a matter of major concern for marine calcifying species. This study investigated the effects of simulated OA on the reproduction of European abalone Haliotis tuberculata and the survival of its offspring. Four-year-old abalone were exposed during reproductive season to two relevant OA scenarios, ambient pH (8.0) and low pH (7.7). After five months of exposure, abalone were induced to spawn. The gametes, larvae and juveniles were then exposed for five months to the same pH conditions as their parents. Several biological parameters involved in adult reproduction as well as in larval, post-larval and juvenile fitness were measured. No effects on gametes, fertilisation or larval oxidative stress response were detected. However, developmental abnormalities and significant decreases in shell length and calcification were observed at veliger stages. The expression profile of a GABA A receptor-like gene appeared to be regulated by pH, depending on larval stage. Larval and post-larval survival was not affected by low pH. However, a lower survival and a reduction of growth were recorded in juveniles at pH 7.7. Our results confirm that OA negatively impacts larval and juvenile fitness and suggest the absence of carry-over effects on abalone offspring. This may compromise the survival of abalone populations in the near future.

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Saving Nemo: extinction risk, conservation status, and effective management strategies for anemonefishes

Anemonefishes share a number of life history and ecological traits, and some unfortunate links to human-induced stress, that expose some of the 28 species to the risk of extinction. The biodiversity hotspot for anemonefishes extends across Southeast Asia to the western Pacific, including many countries where there are high levels of human impact and few effective management strategies. Anemonefish biodiversity is threatened by anemone bleaching, direct effects of ocean warming and acidification, collection for the aquarium trade, and coastal development. These risks are exacerbated by extreme habitat specialization, the mutual anemonefish–anemone relationship, low abundance, low population connectivity, small geographic ranges, and shallow depth ranges. Many species exhibit two or three of these traits, with small range species often associated with fewer anemone hosts and narrower depth ranges, exposing them to double or triple jeopardy. While all species have not been assessed by the IUCN, our detailed analysis of area of occupancy indicates that three species are extremely close to the threshold for being classified as Critically Endangered. Marine reserves have been effective in protecting species from exploitation and helping sustain marginal populations across generations, but effective population sizes are often very small and recovery can be slow. Additional management efforts need to focus on sustainable collecting practices and the protection and restoration of critical anemone habitats.

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Gregarious larval settlement mediates the responses of new recruits of the reef coral Acropora austera to ocean warming and acidification

Gregarious larval settlement represents an important window for chimera formation in reef corals, yet it remains largely unknown how aggregated settlement and early chimerism could modify the performance and responses of coral recruits under elevated temperature and pCO2. In this study, single and aggregated recruits of the broadcast spawning coral Acropora austera were exposed to contrasts of two temperatures (28 versus 30.5°C) and pCO2 levels (~500 versus 1000 μatm) for two weeks, and algal symbiont infection success, survivorship and growth were assessed. Results showed that symbiont infection success was mainly affected by temperature and recruit type, with reduced symbiont infection at increased temperature and consistently higher infection success in chimeric recruits compared to single recruits. Furthermore, although chimeric recruits with larger areal size had significantly higher survivorship in all treatments, the polyp-specific growth rates were considerably lower in chimeric entities than individual recruits. More importantly, the recruit type significantly influenced the responses of recruit polyp-specific growth rates to elevated temperature, with chimeras exhibiting lowered skeletal lateral growth under elevated temperature. These results demonstrate the benefits and costs associated with gregarious larval settlement for juvenile corals under ocean warming and acidification, and highlight the ecological role of larval settlement behavior in mediating the responses of coral recruits to climate change stressors.

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Intergenerational effects of ocean acidification on reproductive traits of an estuarine copepod

Graphical abstract

Copepods are an important part of the marine food web because of their high biomass productivity and nutrient turnover rate compared to other zooplankton in the marine ecosystem. Despite their great ecological role in the ocean, there is only limited information available on the consequences of ocean acidification (OA) induced by the future increase in CO2 on the planet. More specifically, there is almost no information about the impact of OA on the European copepod Calanipeda aquaedulcis Kritschagin, 1873. Therefore, the present investigation hypothesized that OA would not produce negative multigenerational effects on the survival and reproductive performance of this copepod species. Here we assessed, the multigenerational (F1 and F2) effect of OA on eight important reproductive traits (maturity, prosome length, fertility, egg release, hatching success, survival rate, reproductive performance, and the total number of adults per generation). For this study, C. aquaedulcis were collected from the Guadalquivir River (southwest of Spain) and were exposed to four different pH gradients (pH 8.1 as control and pH 7.5, 7.0, 6.5 as acidified conditions) to mimic the future seawater acidification scenarios. The survival rate from nauplius to adult, C. aquaedulcis was significantly reduced by pHs and across generations. Besides, results also indicated that there were marked effects on fertility, reflected by a significantly lower number of eggs per female in each generation. Similarly, hatching success also showed a decreasing pattern towards low pH, and importantly, F1 females had lower hatching success than F0 females. While a beneficial parental effect was detected in the offspring in response to OA, it was insufficient to offset the negative effects caused by it. The findings presented here appear to have ecological significance, as decreasing the reproductive performance of copepods may have a negative impact on the marine food web, as ichthyofaunal feeding and growth are heavily reliant on this component of the food web.

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A transcriptomic analysis of phenotypic plasticity in Crassostrea virginica larvae under experimental acidification

Graphical abstract

Ocean acidification (OA) is a major threat to marine calcifiers, and little is known regarding acclimation to OA in bivalves. This study combined physiological assays with next-generation sequencing to assess the potential for recovery from and acclimation to OA in the eastern oyster (Crassostrea virginica) and identify molecular mechanisms associated with resilience. In a reciprocal transplant experiment, larvae transplanted from elevated pCO(~1400 ppm) to ambient pCO2 (~350 ppm) demonstrated significantly lower mortality and larger size post-transplant than oysters remaining under elevated pCO2 and had similar mortality compared to those remaining in ambient conditions. The recovery after transplantation to ambient conditions demonstrates the ability for larvae to rebound and suggests phenotypic plasticity and acclimation. Transcriptomic analysis supported this hypothesis as genes were differentially regulated under OA stress. Transcriptomic profiles of transplanted and non-transplanted larvae terminating in the same final pCO2 converged, further supporting the idea that acclimation underlies resilience. The functions of differentially expressed genes included cell differentiation, development, biomineralization, ion exchange, and immunity. Results suggest acclimation as a mode of resilience to OA. In addition, the identification of genes associated with resilience can serve as a valuable resource for the aquaculture industry, as these could enable marker-assisted selection of OA-resilient stocks.

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The effects of ocean acidification and temperature rise on the thermal tolerance and critical thermal limit of Pacific herring (Clupea pallasii)

Anthropogenic climate change, including the interactive effects of ocean acidification and temperature rise, is projected to affect marine ecosystems by challenging the environmental tolerance limits of individual species. Such impacts have been documented in a handful of marine fishes, including major physiological effects experienced in early-life stages of Pacific herring, an important forage and commercial fish species widely distributed in coastal systems across the North Pacific. In this study, we investigated the effects of temperatures between 10-16°C and two pCO2 levels (ambient and high pCO2) on hatching and survival of Pacific herring. Survival after acute temperature exposure was assessed and compared between incubation treatments, as may be experienced by herring egg deposits during low tide on warm days. We compared early and late spawning populations to determine if their responses differed when exposed to chronic temperature and pCO2 conditions and to short term temperature stress. A subset of embryos from the 10°C and 16°C treatments were exposed to critical thermal maximum (𝐶𝑇𝑚𝑎𝑥) trials that simulated the acute temperature fluctuations associated with marine heat waves and tidal processes in shallow nearshore habitats. Hatching success was primarily influenced by temperature in both winter and spring embryos. 𝐶𝑇𝑚𝑎𝑥 results indicate that embryos were able to withstand acute exposure to 20°C regardless of spawning population or incubation treatments, but survival was greatly reduced after 2-3 hours at 25°C. Post-exposure heart contraction measurements revealed a greater rate of increase in heart rate in the combined treatment of 10°C and 𝐶𝑇𝑚𝑎𝑥 duration hours compared to 16°C, suggesting respiratory acclimation at higher incubation temperatures. Oxygen consumption rates (MO2) measured at stable incubation conditions resulted in higher MO2 values at elevated temperatures and pCO2 levels. Overall, this study reinforces that Pacific herring are resilient to moderate pCO2 and temperature stress but are vulnerable to acute temperature increases that may accompany marine heatwave events and late season low tide temperatures, and in some cases the combination of elevated pCO2 and temperature can introduce additional challenges for these important forage fish.

Continue reading ‘The effects of ocean acidification and temperature rise on the thermal tolerance and critical thermal limit of Pacific herring (Clupea pallasii)’

Temperature and reduced pH regulate stress and biomineralization gene expression in larvae and post-larvae of the sand dollar Dendraster excentricus

Seawater temperature, oxygen, salinity and pH are important abiotic factors, changes in which can generate stress in marine organisms. Subtidal and intertidal species, such as the sand dollar Dendraster excentricus, are daily exposed to stressors against which they have developed survival mechanisms to face environmental challenges. Analysing the expression of some key genes in response to stress factors due to changes in temperature and pH, especially in the early stages of development, opens a window of knowledge on the effect that these stressors have on benthos marine organisms. In the present work larvae and post-larvae of D. excentricus were exposed to high temperature and low pH scenarios. Survival, size and gene expression of five genes, involved in both stress response (hsp70 IV and hsp90 beta-like) and biomineralization for skeletogenesis (sm29sm30Acarbonic anhydrase 14-like and mitochondrial proton/calcium exchanger protein LOC575637), were analysed in 4-, 6-, 8-arms, competent larvae and post-larvae. Survival of stressed larvae and post-larvae presented a significant decrease, up to 37% in some stages. A size reduction of almost 30 μm was observed when larvae were exposed to stressful conditions, except in competent larvae and in post-larvae where no significant changes were detected. After stress treatments, transcripts of hsp90 beta-like were up-regulated in all larval stages but hsp70 IV transcripts were not. Under tested stressful conditions sm29 and sm30A expression was down-regulated in larvae and post-larvae, while carbonic anhydrase 14-like and LOC575637 expressions were up-regulated. It is evident that tolerance to changes in seawater temperature and pH has a direct effect on metabolic functions of D. excentricus larvae and post-larvae, which depends on the developmental stage. If laboratory results are extrapolated to marine ecosystems, it is possible that populations of this structuring organism may be disturbed with subsequent damage to ecosystem balance, until resilient organisms acclimatize and adapt to their changing habitats.

Continue reading ‘Temperature and reduced pH regulate stress and biomineralization gene expression in larvae and post-larvae of the sand dollar Dendraster excentricus’

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