Posts Tagged 'echinoderms'

An ecotoxicological study on physiological responses of Archaster typicus to salinity, thermal and ocean acidification stressors

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.

Continue reading ‘An ecotoxicological study on physiological responses of Archaster typicus to salinity, thermal and ocean acidification stressors’

Harmful effects of cocaine byproduct in the reproduction of sea urchin in different ocean acidification scenarios

Highlights

• Impact of different acidification scenarios by enrichment of CO2 on contaminants of emerging concern.

• Toxicity of a cocaine byproduct in different scenarios of ocean acidification.

• Combined effects of crack cocaine and low pH on reproduction of sea urchin.

• Hazards and risks of illicit drugs pose to public health and the environment.

Abstract

This study has as main objective assessing the toxicity of crack-cocaine combined with different scenarios of ocean acidification on fertilization rate and embryo-larval development of Echinometra lucunter sea urchin. Effects on early life stages were assessed at five different concentrations (6,25 mg.L-1; 12,5 mg.L-1; 25 mg.L-1; 50 mg.L-1 and 100 mg.L-1) of crack-cocaine at four different pH values (8.5; 8.0; 7.5; 7.0). The pH values were achieved using two different methodologies: adding hydrochloric acid (HCl) and injecting carbon dioxide (CO2). The fertilization test did not show significant differences (p≤0.05) compared with control sample at pH values 8.5; 8.0 and 7.5. Results of embryo-larval assays showed a half maximal effective concentration (EC50) of crack-cocaine at pH values tested (8.5, 8.0, 7.5) as 58.83, 10.67 and 11.58 mg/L-1 for HCl acidification and 58.83, 23.28 and 12.57 mg/L-1 for CO2 enrichment. At pH 7.0 the effects observed in fertilization rate and embryo development were associated with the acidification. This study is the first ecotoxicological assessment of illicit drug toxicity in aquatic ecosystems at different ocean acidification scenarios.

Continue reading ‘Harmful effects of cocaine byproduct in the reproduction of sea urchin in different ocean acidification scenarios’

Marine mass mortality in a global change context: impacts on individuals, populations and communities

Human actions are pushing natural systems into states that have no historical precedent. In response, empirical and theoretical researchers are increasingly focused on developing ways to predict the responses of ecological systems to change. However, significant knowledge gaps remain, often leading to “ecological surprises” where observed impacts of global change do not align with existing theory or hypotheses. In this dissertation, I study the response to perturbations of a well-characterized system for ecological research, the Northeast Pacific rocky intertidal, to advance our understanding of and ability to predict the impacts of global change on individuals, populations and communities. In 2013 and 2014, sea star species along the west coast of North America were affected by an outbreak of Sea Star Wasting Syndrome (SSWS), resulting in an epidemic of mass mortality that spanned unprecedented geographic and temporal scales and resulted in the near extirpation of multiple sea star species from many locations along the coast. One of the species that was most strongly affected in the intertidal zone was Pisaster ochraceus, an iconic predatory sea star that has the ability to play a keystone role in its community through foraging on and ultimately controlling the lower boundary of mussel prey populations. The first two chapters of this dissertation take advantage of SSWS as a “natural” form of top predator removal to assess the consequences of this type of perturbation on ecosystem resilience. In Chapter 2, I tested the hypotheses that P. ochraceus loss would facilitate a population expansion of a smaller, mesopredator sea star, Leptasterias sp., and that this expansion would have negative effects on P. ochraceus population recovery. This result would follow expectations of competitive release and aligns with existing research on the competitive relationship between these species from the Northeast Pacific intertidal. I used field surveys to track Leptasterias populations just before the onset of and up to three years after SSWS. Contrary to expectation, I did not see an increase in the distribution or density of Leptasterias, and instead saw a decrease in individual size post-SSWS. Further, I found no evidence of competition between P. ochraceus recruits and Leptasterias for resources. Thus, although my hypotheses were grounded in theory and previous research, they were not supported by data. These results suggest that Leptasterias will not provide a bottleneck for P. ochraceus population recovery from SSWS, nor compensate for lowered P. ochraceus predation. The dynamics of P. ochraceus at the recruit (early benthic juvenile) life-history stage has long been considered a gap in our understanding of the species, as recruits have been historically rare in the intertidal and hard to study. Post-SSWS, however, many sites along the coast experienced unprecedented recruitment of P. ochraceus into intertidal ecosystems. In Chapter 3, I used a field experiment to test the hypothesis that this pulse of recruitment was facilitated by SSWS-related adult loss, the consequent decrease in predation by adult P. ochraceus, and increase in prey availability for recruits. Instead of finding evidence that adults dominate recruits in food competition and inhibit recruit success, I found that recruits have a negative effect on P. ochraceus adult densities. Further, treatments where recruits were excluded and only adults had access to prey communities showed the highest control of sessile invertebrate prey populations at the end of the year-long experiment. Thus, these results suggest that adult P. ochraceus will not hinder recruit recovery, but propose a mechanism whereby high recruit densities may increase vulnerability to SSWS-induced shifts in community structure. Outbreaks of mass mortality, particularly those as widespread as SSWS, are one of many ecological challenges driven by anthropogenic environmental changes such as warming and ocean acidification. However, predicting the vulnerability of species and populations to global change is an ongoing and significant challenge for researchers and managers. In Chapter 4 I assessed whether intraspecific physiological variability could help predict P. ochraceus recruit response to ocean acidification and warming. I found that individual metabolic rate interacted with ocean acidification and food availability to drive sea star growth, and that an interaction between metabolic rate and temperature also predicted sea star predation on Mytilus spp. mussels. Thus, these results have implications not only for P. ochraceus but also for its food web interactions. Incorporating these results into predictive frameworks may improve our ability to anticipate and scale up responses to global change across levels of ecological organization. In summary, my dissertation, although chock-full of surprises, presents several paths forward for improving predictive ability in the face of accelerating anthropogenic global changes. Further, we reinforce the notion that management strategies should be cautious and anticipate ecological surprises. Predicting the future is challenging even when predictions are well-informed, particularly in environmental contexts that have never been encountered before.

Continue reading ‘Marine mass mortality in a global change context: impacts on individuals, populations and communities’

Transcriptional profiles of early stage red sea urchins (Mesocentrotus franciscanus) reveal differential regulation of gene expression across development

The red sea urchin, Mesocentrotus franciscanus, is an ecologically important kelp forest species that also serves as a valuable fisheries resource. In this study, we have assembled and annotated a developmental transcriptome for M. franciscanus that represents eggs and six stages of early development (8- to 16-cell, morula, hatched blastula, early gastrula, prism and early pluteus). Characterization of the transcriptome revealed distinct patterns of gene expression that corresponded to major developmental and morphological processes. In addition, the period during which maternally-controlled transcription was terminated and the zygotic genome was activated, the maternal-to-zygotic transition (MZT), was found to begin during early cleavage and persist through the hatched blastula stage, an observation that is similar to the timing of the MZT in other sea urchin species. The presented developmental transcriptome will serve as a useful resource for investigating, in both an ecological and fisheries context, how the early developmental stages of this species respond to environmental stressors.

Continue reading ‘Transcriptional profiles of early stage red sea urchins (Mesocentrotus franciscanus) reveal differential regulation of gene expression across development’

Effects of coralline algal diffusion boundary layers on growth of newly settled sea urchins: implications for ocean acidification conditions

Macroalgae are able to modify their local environment via biological processes, thereby creating a diffusive boundary layer (DBL) where the chemical and physical environment differs from the overlying bulk seawater. In slow flow environments, the DBL has the potential to modulate effects of reduced seawater pH associated with ocean acidification (OA). OA poses a major threat to marine ecosystems and particularly to calcifying organisms. While implications for macroalgae and corals in the DBL have been studied, the effects on invertebrates settling and inhabiting the DBL are not well understood. This study examines
the oxygen and pH conditions within coralline algal DBLs that change as a result of irradiance, flow and bulk seawater pH, in order to understand the effects of these variable conditions on growth of juvenile sea urchins in the DBL. Oxygen concentrations, used as a proxy for pH based on previous research, were measured above crustose coralline algal surfaces to determine DBL thickness and pH levels within the DBL. Newly settled juvenile sea urchins Pseudechinus huttoni were subsequently grown in these conditions for up to 11 days. Morphological measurements (test diameter and spine length) and scanning electron microscopy were used to examine growth and calcification of sea urchins.

Seawater pH levels above CCA varied as a result of irradiance, flow and bulk seawater pH. In static flow, CCA increased pH at its surface up to approximately 0.8 units above the overlying bulk seawater in the light, but only decreased pH up to nearly 0.09 units below bulk seawater in the dark. DBLs were thickest at zero or slow flow (1 cm s-1 ) in the light. pH levels in the DBL varied from approximately pHT 7.4 to 8.6, but there was no strong effect of these varying pH levels within the DBL on post-settlement growth of P. huttoni juveniles. Life in
the diffusion boundary has allowed juveniles to adapt to grow and calcify in naturally fluctuating pH environments. This finding supports observations seen in other juvenile sea urchins, and is significant because it indicates that the early post-settlement stage may not be as sensitive to OA as the larval stage, where negative effects have been previously documented. Life in thick diffusion boundary layers above CCA in slow-flow fjord environments may have increased tolerance of juvenile P. huttoni to reduced bulk seawater pH, thereby conferring greater resilience to future ocean acidification conditions.

Continue reading ‘Effects of coralline algal diffusion boundary layers on growth of newly settled sea urchins: implications for ocean acidification conditions’

The importance of inter‐individual variation in predicting species’ responses to global change drivers

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

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Rare genetic variation and balanced polymorphisms are important for survival in global change conditions

Standing genetic variation is important for population persistence in extreme environmental conditions. While some species may have the capacity to adapt to predicted average future global change conditions, the ability to survive extreme events is largely unknown. We used single-generation selection experiments on hundreds of thousands of Strongylocentrotus purpuratus sea urchin larvae generated from wild-caught adults to identify adaptive genetic variation responsive to moderate (pH 8.0) and extreme (pH 7.5) low-pH conditions. Sequencing genomic DNA from pools of larvae, we identified consistent changes in allele frequencies across replicate cultures for each pH condition and observed increased linkage disequilibrium around selected loci, revealing selection on recombined standing genetic variation. We found that loci responding uniquely to either selection regime were at low starting allele frequencies while variants that responded to both pH conditions (11.6% of selected variants) started at high frequencies. Loci under selection performed functions related to energetics, pH tolerance, cell growth and actin/cytoskeleton dynamics. These results highlight that persistence in future conditions will require two classes of genetic variation: common, pH-responsive variants maintained by balancing selection in a heterogeneous environment, and rare variants, particularly for extreme conditions, that must be maintained by large population sizes.

Continue reading ‘Rare genetic variation and balanced polymorphisms are important for survival in global change conditions’


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Ocean acidification in the IPCC AR5 WG II

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