How do multiple coastal stressors structure the genomic diversity of marine populations?

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Marine species face a complex suite of stressors that span multiple temporal and spatial scales from long-term global ocean change to localized episodes of coastal acidification. The cumulative and concurrent impacts of multiple stressors remain relatively unknown and requires investigating their synergistic impacts across all life stages. Two common stressors in coastal environments are hypoxia, or low dissolved oxygen, and coastal acidification. Hypoxia and coastal acidification are linked to daily cycles of respiration and photosynthesis, even in pristine bays and estuaries. Coastal waters are also affected by pulses of natural and artificial freshwater runoff driven by rainfall and storm events. Pulses of freshwater can cause short-term, low salinity conditions, another stressor, that are expected to worsen with climate change. For many marine species, larval stages are the only means of migration and genetic exchange, and larvae are likely encountering hypoxia, coastal acidification, and low salinity stressors while they are in shallow coastal waters. Additionally, early juveniles may encounter extended periods of all three stressors. The interaction of early life-history stages with repeated and combinations of coastal stressors has the potential to result in an increase of larval/juvenile mortality or the removal of less tolerant larvae. The consequences of this differential mortality are being investigated in the eastern oyster using laboratory multi-stressor exposure experiments and in the field through genomic surveys of natural populations. Patterns of genetic selection are being analyzed by combining genomic and environmental data to elucidate how multiple stressors are shaping marine populations. Broader impacts include training opportunities for a post-doctoral fellow, graduate and undergraduate students and societal impacts. Results from the study are key to predicting how oyster reefs will adapt to long-term climate change and human population growth. A symposium is planned to bring scientists and members of the broader community together to discuss conservation and restoration of oyster reefs and sustainable aquaculture. A better understanding the physiological limits of larvae and juveniles to stressors is contributing to new strategies for oyster hatcheries to optimize selection and screening of brood stock for robust larvae and juveniles.The broad goal is to characterize how hypoxia (DO), coastal acidification (CA), and low salinity events (LS) shape population connectivity and microevolutionary processes of marine invertebrates. As larvae grow and develop, they may be able to tolerate short-term exposures to environmental stressors, but prolonged exposure to diurnal DO/CA cycling and LS events may reduce subsequent survival, especially in juveniles. Larval and juvenile interactions with multiple stressors have the potential to either disrupt gene flow by simply not allowing migrant exchange or to act as a selective force, structuring populations through genotype-environment interactions. This project uses a coupled experimental and seascape genomics approach to investigate how multiple stressors are shaping observed genomic diversity. Phase 1 is determining how larval and juvenile genotypes and phenotypes respond to multiple stressors across different developmental time points. Experiments include two larval short-term exposures to factorial combinations of DO/CA and LS, and a long-term juvenile exposure to factorial combinations of DO/CA diurnal cycling and LS. The coding regions of genes expressed during experimental exposures are being sequenced using a cost-effective exome capture method. Phase 2 is determining the role of natural and anthropogenic forces shaping the evolution of oyster populations by testing if selective regimes differ and interact across life-history stages and if the frequencies of both neutral and resistant genotypes correlate with environmental conditions. Surveys of the genomes of adult populations across multiple localities from several urbanized estuaries are generating a seascape genomic framework based on a panel of genomic markers, including potential loci under selection during early-life history. These data are being integrated with environmental data to elucidate the mix of factors that contribute to population structure and local genetic diversity. Results are linking adult genotype frequencies at both neutral and putatively selective loci to changes in allele frequencies in response to early larval, late larval, and early juvenile exposure to stressors. The research is unraveling the complex interaction of selection, migration, and drift on marine genetic diversity for a mechanistic understanding of the genomic consequences of coastal stressor and their interaction on larvae.This project is jointly funded by Biological Oceanography and Integrative Organismal Systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.