Population genetics of native shellfish aquaculture species and potential genetic risks of cultivation

Native shellfish aquaculture has many benefits, but interbreeding of hatchery and wild populations may pose genetic risks to wild populations. The type and magnitude of these risks depends in part on the genetic population structure of native shellfish species. Early genetic studies on marine shellfish provided little evidence for such structure. However, recent population genetic studies provide higher resolution, make use of both neutral and non-neutral molecular markers, and suggest some marine shellfish can exhibit population structure and even local adaptation. Here, we present preliminary results on genetic differentiation among populations of Crassadoma gigantea (the purple-hinged rock scallop) and Parastichopus californicus (the giant California sea cucumber), two native species that are currently being developed for aquaculture production in Puget Sound. Data for both species demonstrate high levels of genetic diversity and indications for population structuring by geography. Additionally, data for P. californicus suggest a potential cryptic species. Results will be used in a genetic risk model to quantify risk under multiple management scenarios, which will provide decision support to resource managers and other stakeholders. Our study shows the importance of population structure for genetic risk assessment and the power of combining empirical data, computer modeling and end-user input

Metabolic recovery and compensatory shell growth of juvenile Pacific geoduck \u3cem\u3ePanopea generosa\u3c/em\u3e following short-term exposure to acidified seawater

While acute stressors can be detrimental, environmental stress conditioning can improve performance. To test the hypothesis that physiological status is altered by stress conditioning, we subjected juvenile Pacific geoduck, Panopea generosa, to repeated exposures of elevated pCO2 in a commercial hatchery setting followed by a period in ambient common garden. Respiration rate and shell length were measured for juvenile geoduck periodically throughout short-term repeated reciprocal exposure periods in ambient (~550 μatm) or elevated (~2400 μatm) pCO2 treatments and in common, ambient conditions, 5 months after exposure. Short-term exposure periods comprised an initial 10-day exposure followed by 14 days in ambient before a secondary 6-day reciprocal exposure. The initial exposure to elevated pCO2 significantly reduced respiration rate by 25% relative to ambient conditions, but no effect on shell growth was detected. Following 14 days in common garden, ambient conditions, reciprocal exposure to elevated or ambient pCO2 did not alter juvenile respiration rates, indicating ability for metabolic recovery under subsequent conditions. Shell growth was negatively affected during the reciprocal treatment in both exposure histories; however, clams exposed to the initial elevated pCO2 showed compensatory growth with 5.8% greater shell length (on average between the two secondary exposures) after 5 months in ambient conditions. Additionally, clams exposed to the secondary elevated pCO2 showed 52.4% increase in respiration rate after 5 months in ambient conditions. Early exposure to low pH appears to trigger carryover effects suggesting bioenergetic re-allocation facilitates growth compensation. Life stage-specific exposures to stress can determine when it may be especially detrimental, or advantageous, to apply stress conditioning for commercial production of this long-lived burrowing clam

Differential response to stress in Ostrea lurida as measured by gene expression

Olympia oysters are the only oyster native to the west coast of North America. The population within Puget Sound, WA has been decreasing significantly since the early 1900’s. Current restoration efforts are focused on supplementing local populations with hatchery bred oysters. A recent study by Heare et al. (2017) has shown differences in stress response in oysters from different locations in Puget Sound however, nothing is known about the underlying mechanisms associated with these observed differences. In this study, expression of genes associated with growth, immune function, and gene regulatory activity in oysters from Oyster Bay, Dabob Bay, and Fidalgo Bay were characterized following temperature and mechanical stress. We found that heat stress and mechanical stress significantly changed expression in molecular regulatory activity and immune response, respectively. We also found that oysters from Oyster Bay had the most dramatic response to stress at the gene expression level. These data provide important baseline information on the physiological response of Ostrea lurida to stress and provide clues to underlying performance differences in the three populations examined

Seawater carbonate chemistry and performance and oxidative status in a tolerant burrowing clam

Whereas low levels of thermal stress, irradiance, and dietary restriction can have beneficial effects for many taxa, stress acclimation remains understudied in marine invertebrates, despite being threatened by climate change stressors such as ocean acidification. To test for life-stage and stress-intensity dependence in eliciting enhanced tolerance under subsequent stress encounters, we initially conditioned pediveliger Pacific geoduck (Panopea generosa) larvae to (i) ambient and moderately elevated pCO2 (920 µatm and 2800 µatm, respectively) for 110 days, (ii) secondarily applied a 7-day exposure to ambient, moderate, and severely elevated pCO2 (750 µatm, 2800 µatm, and 4900 µatm, respectively), followed by 7 days in ambient conditions, and (iii) implemented a 7-day third exposure to ambient (970 µatm) and moderate pCO2 (3000 µatm). Initial conditioning to moderate pCO2 stress followed by second and third exposure to severe and moderate pCO2 stress increased respiration rate, organic biomass, and shell size suggesting a stress-intensity-dependent effect on energetics. Additionally, stress-acclimated clams had lower antioxidant capacity compared to clams under ambient conditions, supporting the hypothesis that stress over postlarval-to-juvenile development affects oxidative status later in life. Time series and stress intensity-specific approaches can reveal life-stages and magnitudes of exposure, respectively, that may elicit beneficial phenotypic variation

At the whim of the tides: Measuring population connectivity of Olympia oysters (Ostrea lurida) in Puget Sound

Targeting restoration efforts to promote population connectivity, the exchange of individuals among geographically separated subpopulations, is a key element of successful management of declining marine species. Olympia oysters (Ostrea lurida), a species of concern in Washington State, have failed to fully recover after both over exploitation and environmental degradation. Although state agencies and environmental groups have made it a priority to restore O. lurida because they are native to the west coast of North America and provide key habitat and ecosystem services to the Salish Sea., our understanding of O. lurida population connectivity remains limited, in part because little is known about their migratory larvae. Brooded Olympia oyster larvae incorporate trace elements present in estuarine waters into their shell, creating a chemical “signature” of their natal site before release and dispersal. With the use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), the provenance signatures of larvae and recruits can be compared, and potentially matched, to signatures of source populations. In this study, larval source and recruitment were investigated via plankton pumping and settlement monitoring at two populations of O. lurida in Puget Sound: Fidalgo Bay, an enhanced subpopulation, and Dyes Inlet, one of the few remaining natural oyster beds. To create a base map of chemical signatures in Puget Sound, brooded larvae were collected from 13 distinct O. lurida locales. While sampling for brooded larvae we collected comprehensive reproduction and shell size data on Puget Sound populations of O. lurida. The results of this study will directly influence management efforts to restore O. lurida; resource managers will be able to identify both source populations of larvae, where seed enhancement would be the most effective restoration tool and sink subpopulations where habitat enhancement would be more beneficial

Seawater carbonate chemistry of experiment on acclimatory gene expression of primed clams enhances robustness to elevated pCO2

Sublethal exposure to environmental challenges may enhance ability to cope with chronic or repeated change, a process known as priming. In a previous study, pre-exposure to seawater enriched with pCO2 improved growth and reduced antioxidant capacity of juvenile Pacific geoduck Panopea generosa clams, suggesting that transcriptional shifts may drive phenotypic modifications post-priming. To this end, juvenile clams were sampled and TagSeq gene expression data were analysed after (i) a 110-day acclimation under ambient (921 μatm, naïve) and moderately elevated pCO2 (2870 μatm, pre-exposed); then following (ii) a second 7-day exposure to three pCO2 treatments (ambient: 754 μatm; moderately elevated: 2750 μatm; severely elevated: 4940 μatm), a 7-day return to ambient pCO2 and a third 7-day exposure to two pCO2 treatments (ambient: 967 μatm; moderately elevated: 3030 μatm). Pre-exposed geoducks frontloaded genes for stress and apoptosis/innate immune response, homeostatic processes, protein degradation and transcriptional modifiers. Pre-exposed geoducks were also responsive to subsequent encounters, with gene sets enriched for mitochondrial recycling and immune defence under elevated pCO2 and energy metabolism and biosynthesis under ambient recovery. In contrast, gene sets with higher expression in naïve clams were enriched for fatty-acid degradation and glutathione components, suggesting naïve clams could be depleting endogenous fuels, with unsustainable energetic requirements if changes in carbonate chemistry persist. Collectively, our transcriptomic data indicate that pCO2 priming during post-larval periods could, via gene expression regulation, enhance robustness in bivalves to environmental change. Such priming approaches may be beneficial for aquaculture, as seafood demand intensifies concurrent with increasing climate change in marine systems

Repeat exposure to hypercapnic seawater modifies growth and oxidative status in a tolerant burrowing clam

Although low levels of thermal stress, irradiance and dietary restriction can have beneficial effects for many taxa, stress acclimation remains little studied in marine invertebrates, even though they are threatened by climate change stressors such as ocean acidification. To test the role of life-stage and stress-intensity dependence in eliciting enhanced tolerance under subsequent stress encounters, we initially conditioned pediveliger Pacific geoduck (Panopea generosa) larvae to ambient and moderately elevated PCO2 (920 μatm and 2800 μatm, respectively) for 110 days. Then, clams were exposed to ambient, moderate or severely elevated PCO2 (750, 2800 or 4900 μatm, respectively) for 7 days and, following 7 days in ambient conditions, a 7-day third exposure to ambient (970 μatm) or moderate PCO2 (3000 μatm). Initial conditioning to moderate PCO2 stress followed by second and third exposure to severe and moderate PCO2 stress increased respiration rate, organic biomass and shell size, suggesting a stress-intensity-dependent effect on energetics. Additionally, stressacclimated clams had lower antioxidant capacity compared with clams under ambient conditions, supporting the hypothesis that stress over postlarval-to-juvenile development affects oxidative status later in life. Time series and stress intensity-specific approaches can reveal life-stages and magnitudes of exposure, respectively, that may elicit beneficial phenotypic variation

Assessing Local Adaptation and the Response to Ocean Acidification in Rock Scallops to Inform Aquaculture Practice

The shellfish aquaculture industry is among the first economic sectors to be negatively affected by ocean acidification, in part because changes in water chemistry interfere with shell formation and reduce survival and productivity. Populations already adapted to low pH may represent important genetic resources for the development of resistant strains. The protection of such genetic resources is of crucial importance in a rapidly changing environment, adding to traditional concerns of genetic interactions between wild and captive populations. The purple-hinged rock scallop (Crassadoma gigantea), a species native to the U.S. Pacific coast, is currently under consideration for commercial aquaculture. Across their range, rock scallops may exhibit population structure due to restricted gene flow and local adaptation that should be conserved. We will use whole genome scans of wild scallops to measure the degree of population structure and local adaptation at two spatial scales: among wild populations in California, Washington, and Alaska, and among wild populations within Washington. We will quantify neutral genetic divergence, explore molecular evidence for adaptive genetic differentiation, and identify discriminatory markers for routine screening of wild populations and captive broodstock. In addition, we will use a common garden experiment with an elevated pCO2 treatment to directly compare performance of larval families from California, Washington, and Alaska. Our findings will inform resource managers and aquaculture practitioners, and contribute to wild stock resilience and the sustainability of C. gigantea aquaculture