Posts Tagged 'echinoderms'



Unique genomic and phenotypic responses to extreme and variable pH conditions in purple urchin larvae

Environmental variation experienced by a species across space and time can promote the maintenance of genetic diversity that may be adaptive in future global change conditions. Selection experiments have shown that purple sea urchin, Strongylocentrotus purpuratus, populations have adaptive genetic variation for surviving pH conditions at the “edge” (pH 7.5) of conditions experienced in nature. However, little is known about whether populations have genetic variation for surviving low-pH events beyond those currently experienced in nature or how variation in pH conditions affects organismal and genetic responses. Here, we quantified survival, growth, and allele frequency shifts in experimentally selected developing purple sea urchin larvae in static and variable conditions at three pH levels: pH 8.1 (control), pH 7.5 (edge-of-range), and pH 7.0 (extreme). Variable treatments recovered body size relative to static treatments, but resulted in higher mortality, suggesting a potential tradeoff between survival and growth under pH stress. However, within each pH level, allele frequency changes were overlapping between static and variable conditions, suggesting a shared genetic basis underlying survival to mean pH regardless of variability. In contrast, genetic responses to pH 7.5 (edge) versus pH 7.0 (extreme) conditions were distinct, indicating a unique genetic basis of survival. In addition, loci under selection were more likely to be in exonic regions than regulatory, indicating that selection targeted protein-coding variation. Loci under selection in variable pH 7.5 conditions, more similar to conditions periodically experienced in nature, performed functions related to lipid biosynthesis and metabolism, while loci under selection in static pH 7.0 conditions performed functions related to transmembrane and mitochondrial processes. While these results are promising in that purple sea urchin populations possess genetic variation for surviving extreme pH conditions not currently experienced in nature, they caution that increased acidification does not result in a linear response but elicits unique physiological stresses and survival mechanisms.

Continue reading ‘Unique genomic and phenotypic responses to extreme and variable pH conditions in purple urchin larvae’

Testing multiple climate stressors at the cold range limit of a marine calcifier

Coastal marine ecosystems have been identified as a particularly high risk from global climate change. Laboratory mesocosm experiments with model organisms can be useful in elucidating the effects of multiple climate change stressors on marine species. Here I examine the combined effects of marine heatwaves (MHWs) and ocean acidification (OA) on early embryonic development of the sea urchin Arbacia punctulata taken from its cold (northern) range limit in the Northwest Atlantic. I observed additive effects of MHWs and OA on developmental rates, with rates enhanced by MHWs and hindered by OA as compared to ambient conditions. Hence, MHWs mitigated a negative effect of OA on development of the species at its cold range limit. My results provide an improved understanding of how MHWs and OA can combine to affect the sensitive early life-history stages of calcifying marine invertebrates and may be useful in predicting future shifts in species distributions.

Continue reading ‘Testing multiple climate stressors at the cold range limit of a marine calcifier’

Toward a mechanistic understanding of marine invertebrate behavior at elevated CO2

Elevated carbon dioxide (CO2) levels can alter ecologically important behaviors in a range of marine invertebrate taxa; however, a clear mechanistic understanding of these behavioral changes is lacking. The majority of mechanistic research on the behavioral effects of elevated CO2 has been done in fish, focusing on disrupted functioning of the GABAA receptor (a ligand-gated ion channel, LGIC). Yet, elevated CO2 could induce behavioral alterations through a range of mechanisms that disturb different components of the neurobiological pathway that produces behavior, including disrupted sensation, altered behavioral choices and disturbed LGIC-mediated neurotransmission. Here, we review the potential mechanisms by which elevated CO2 may affect marine invertebrate behaviors. Marine invertebrate acid–base physiology and pharmacology is discussed in relation to altered GABAA receptor functioning. Alternative mechanisms for behavioral change at elevated CO2 are considered and important topics for future research have been identified. A mechanistic understanding will be important to determine why there is variability in elevated CO2-induced behavioral alterations across marine invertebrate taxa, why some, but not other, behaviors are affected within a species and to identify which marine invertebrates will be most vulnerable to rising CO2 levels.

Continue reading ‘Toward a mechanistic understanding of marine invertebrate behavior at elevated CO2’

Transgenerational plasticity and acclimation of tropical sea urchins to ocean warming and acidification

Anthropogenic CO2 emissions are causing the oceans to simultaneously warm and become increasingly acidic, with rates of change that are putting evolutionary pressure on many marine organisms. As a result, both short-term responses and the ability of organisms to acclimate to rapid environmental change through phenotypic plasticity are expected to play a considerable role in persistence of many species under future ocean change. Evidence is accumulating that non-genetic inheritance and transgenerational plasticity (TGP) may be important mechanisms which may facilitate acclimation to ocean warming and acidification. This thesis tests the overarching hypothesis that TGP and parental acclimation to predicted ocean warming and acidification conditions promote greater resilience in offspring using two tropical sea urchins, Tripneustes gratilla and Echinometra sp. A, as model organisms.

Continue reading ‘Transgenerational plasticity and acclimation of tropical sea urchins to ocean warming and acidification’

Temporal variability modulates pH impact on larval sea urchin development

Coastal organisms reside in highly dynamic habitats. Global climate change is expected to alter not only the mean of the physical conditions experienced but also the frequencies and/or the magnitude of fluctuations of environmental factors. Understanding responses in an ecologically relevant context is essential for formulating management strategies. In particular, there are increasing suggestions that exposure to fluctuations could alleviate the impact of climate change-related stressors by selecting for plasticity that may help acclimatization to future conditions. However, it remains unclear whether the presence of fluctuations alone is sufficient to confer such effects or whether the pattern of the fluctuations matters. Therefore, we investigated the role of frequency and initial conditions of the fluctuations on performance by exposing larval sea urchin Heliocidaris crassispina to either constant or fluctuating pH. Reduced pH alone (pH 7.3 vs 8.0) did not affect larval mortality but reduced the growth of larval arms in the static pH treatments. Changes in morphology could affect the swimming mechanics for these small organisms, and geometric morphometric analysis further suggested an overall shape change such that acidified larvae had more U-shaped bodies and shorter arms, which would help maintain stability in moving water. The relative negative impact of lower pH, computed as log response ratio, on larval arm development was smaller when larvae were exposed to pH fluctuations, especially when the change was less frequent (48- vs 24-h cycle). Furthermore, larvae experiencing an initial pH drop, i.e. those where the cycle started at pH 8.0, were more negatively impacted compared with those kept at an initial pH of 7.3 before the cycling started. Our observations suggest that larval responses to climate change stress could not be easily predicted from mean conditions. Instead, to better predict organismal performance in the future ocean, monitoring and investigation of the role of real-time environmental fluctuations along the dispersive pathway is key.

Continue reading ‘Temporal variability modulates pH impact on larval sea urchin development’

Examining the role of DNA methylation in transcriptomic plasticity of early stage sea urchins: developmental and maternal effects in a kelp forest herbivore

Gene expression plasticity can confer physiological plasticity in response to the environment. However, whether epigenetic marks contribute to the dynamics of gene expression is still not well described in most marine invertebrates. Here, we explored the extent and molecular basis of intra- and intergenerational plasticity in the purple sea urchin, Strongylocentrotus purpuratus, by examining relationships between changes in DNA methylation, transcription, and embryo spicule length. Adult urchins were conditioned in the lab for 4 months to treatments that represent upwelling (∼1200 μatm pCO2, 13°C) and non-upwelling conditions (∼500 μatm pCO2, 17°C). Embryos spawned from conditioned adults were reared in either the same adult treatment or the reciprocal condition. Maternal conditioning resulted in significantly differentially methylated CpG sites and differential gene expression in embryos, despite no evidence of maternal effects on embryo spicule length. In contrast, conditions experienced during development resulted in significant differences in embryo spicule length. Intragenerational plasticity in spicule length was strongly correlated to transcriptomic plasticity, despite low levels of intragenerational plasticity in CpG methylation. We find plasticity in DNA methylation and gene expression in response to different maternal environments and these changes have similarities across broad functional groups of genes; yet exhibit little overlap on a gene-by-gene basis. Our results suggest that different forms of environmentally induced plasticity are observable across different time scales and that DNA methylation dynamics may be uncoupled from fast transcriptional responses to the environment and whole organism traits. Overall, this study illuminates the extent to which environmental differences can induce both intra- and intergenerational phenotypic plasticity in a common kelp forest herbivore.

Continue reading ‘Examining the role of DNA methylation in transcriptomic plasticity of early stage sea urchins: developmental and maternal effects in a kelp forest herbivore’

Influence of water masses on the biodiversity and biogeography of deep-sea benthic ecosystems in the North Atlantic

Circulation patterns in the North Atlantic Ocean have changed and re-organized multiple times over millions of years, influencing the biodiversity, distribution, and connectivity patterns of deep-sea species and ecosystems. In this study, we review the effects of the water mass properties (temperature, salinity, food supply, carbonate chemistry, and oxygen) on deep-sea benthic megafauna (from species to community level) and discussed in future scenarios of climate change. We focus on the key oceanic controls on deep-sea megafauna biodiversity and biogeography patterns. We place particular attention on cold-water corals and sponges, as these are ecosystem-engineering organisms that constitute vulnerable marine ecosystems (VME) with high associated biodiversity. Besides documenting the current state of the knowledge on this topic, a future scenario for water mass properties in the deep North Atlantic basin was predicted. The pace and severity of climate change in the deep-sea will vary across regions. However, predicted water mass properties showed that all regions in the North Atlantic will be exposed to multiple stressors by 2100, experiencing at least one critical change in water temperature (+2°C), organic carbon fluxes (reduced up to 50%), ocean acidification (pH reduced up to 0.3), aragonite saturation horizon (shoaling above 1000 m) and/or reduction in dissolved oxygen (>5%). The northernmost regions of the North Atlantic will suffer the greatest impacts. Warmer and more acidic oceans will drastically reduce the suitable habitat for ecosystem-engineers, with severe consequences such as declines in population densities, even compromising their long-term survival, loss of biodiversity and reduced biogeographic distribution that might compromise connectivity at large scales. These effects can be aggravated by reductions in carbon fluxes, particularly in areas where food availability is already limited. Declines in benthic biomass and biodiversity will diminish ecosystem services such as habitat provision, nutrient cycling, etc. This study shows that the deep-sea VME affected by contemporary anthropogenic impacts and with the ongoing climate change impacts are unlikely to withstand additional pressures from more intrusive human activities. This study serves also as a warning to protect these ecosystems through regulations and by tempering the ongoing socio-political drivers for increasing exploitation of marine resources.

Continue reading ‘Influence of water masses on the biodiversity and biogeography of deep-sea benthic ecosystems in the North Atlantic’

Ocean change within shoreline communities: from biomechanics to behaviour and beyond

Humans are changing the physical properties of Earth. In marine systems, elevated carbon dioxide concentrations are driving notable shifts in temperature and seawater chemistry. Here, we consider consequences of such perturbations for organism biomechanics and linkages amongst species within communities. In particular, we examine case examples of altered morphologies and material properties, disrupted consumer–prey behaviours, and the potential for modulated positive (i.e. facilitative) interactions amongst taxa, as incurred through increasing ocean acidity and rising temperatures. We focus on intertidal rocky shores of temperate seas as model systems, acknowledging the longstanding role of these communities in deciphering ecological principles. Our survey illustrates the broad capacity for biomechanical and behavioural shifts in organisms to influence the ecology of a transforming world.

Continue reading ‘Ocean change within shoreline communities: from biomechanics to behaviour and beyond’

Planktonic stages of the ecologically important sea urchin, Diadema africanum: larval performance under near future ocean conditions

Diadema africanum is a recently described sea urchin from the Eastern Atlantic archipelagos, and adults play a major ecological role mediating the transition between two alternative ecosystem states: macroalgal beds and urchin barrens. The aim of this study was to describe for the first time the egg characteristics, fertilization and larval development. To determine basic life-history characteristics for this species, we reared larvae through to metamorphic competence under an energy shortage experiment and temperature–pH experiments to characterize the morphological plasticity of larval responses to actual and future oceanic conditions. D. africanum produces eggs that are larger both in diameter (82.7 μm) and volume (0.30 nl) than the eggs of both Diadema antillarum (70.0 μm, 0.18 nl) and Diadema mexicanum (68.0 μm, 0.16 nl). Larval development is similar to other species within the Family Diadematidae, with a Echinopluteus transversus larval type morphology. The combined effects of the climate change-related environmental factors resulted in a reduction in fitness of D. africanum at the warmer limit of its thermal range when combined with low pH. Results suggest that the egg and larval life-history characteristics of D. africanum may have evolved to facilitate long-distance oceanic transport; however, near-future oceanic conditions may compromise larval survival.

Continue reading ‘Planktonic stages of the ecologically important sea urchin, Diadema africanum: larval performance under near future ocean conditions’

Sea urchin larvae show resilience to ocean acidification at the time of settlement and metamorphosis

Highlights

• Settlement success in Evechinus chloroticus larvae was unaffected when presented with a range of reduced seawater pH (pH 7.0 to ambient) at the time of settlement (no direct effects).

• When presented with crustose coralline algae (CCA) pre-conditioned at either ambient pH or reduced pH 7.7 for 28 days (no indirect effects) at the time of settlement, larval settlement success in E. chloroticus remained unaltered.

• E. chloroticus larvae did not lose their ability to recognize their preferred settlement substrate when exposed to reduced seawater pH at the time of settlement.

• No interactions were observed between the direct (seawater pH) and indirect (preconditioned substrates) effects of reduced pH on E. choroticus settlement success.

Abstract

Extensive research has shown that the early life stages of marine organisms are sensitive to ocean acidification (OA). Less is known, however, on whether larval settlement and metamorphosis may be affected, or by which mechanisms. These are key processes in the life cycle of most marine benthic organisms, since they mark the transition between the free swimming larval stage to the benthic life. We investigated whether OA could affect the larval settlement success of the sea urchin Evechinus chloroticus, a key coastal species with ecological, economic and cultural importance in New Zealand. We performed four settlement experiments to test whether reduced seawater pH (ranging from 8.1 to 7.0, at an interval of ∼0.2 pH units) alters larval settlement and metamorphosis success. Our results show that settlement success was not significantly reduced when the larvae were exposed to a range of reduced seawater pH treatments (8.1–7.0) at time of settlement (direct effects). Similarly, when presented with crustose coralline algae (CCA) pre-conditioned in different seawater pH of either pH 8.1 or 7.7 for 28 days, larval settlement success remained unaltered (indirect effects). We conclude that competent larvae in this species are resilient to OA at time of settlement. Further research on a range of taxa that vary in settlement selectivity and behaviour is needed in order to fully understand the effects of OA on the life cycle of marine invertebrates and the consequences it might have for future coastal marine ecosystems.

Continue reading ‘Sea urchin larvae show resilience to ocean acidification at the time of settlement and metamorphosis’


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Ocean acidification in the IPCC AR5 WG II

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