Coastal ecosystems worldwide are facing an increasing number of anthropogenic stressors, and yet concurrent and cumulative impacts of multiple stressors remain relatively unknown, especially across critical early life stages. Two prevalent and often coupled stressors in shallow coastal waters are hypoxia, or low dissolved oxygen (LO), and coastal acidification (CA), which are driven by diel cycles. Pulses of freshwater are also observed, causing short-term low salinity (LS) conditions and altering carbonate chemistry. Global climate change is expected to alter salinity regimes in estuaries and intensify the magnitude and duration of both LO and CA events.
Here we investigated the responses of larval and juvenile Eastern oysters Crassostrea virginica exposed to four different treatment levels: control, combined LO and CA (1 mgO2/L and 7.0 pH units), LS (10 ppt), and interaction LO/CA+LS. First, oyster larvae, obtained from wild populations in Narragansett Bay, have experienced early (pediveliger stage) and late (eyed-pediveliger stage) larval exposure to the four experimental treatments for 24 and 36h, respectively. Second, the newly settled juveniles were exposed to either ambient conditions or diurnal LO/CA cycling for 11 weeks. This long-term juvenile exposure was associated with regular 48h exposures to the previous four treatments, representing constant, short-term and intense LO/CA and LS events. Both larval and juvenile oysters were sampled for growth, survival and genomic analysis. Preliminary results of the experiment will be presented at the meeting. Subsequently, this study will help determine how short- and long-term exposures to multiple stressors during early life-history stages affect the distribution of genomic diversity across Eastern oyster populations.