Climate variability influences recruitment in a multi-decadal time series

Background/Question/Methods Estuaries along upwelling coasts naturally experience variability in water chemistry and temperature at multiple temporal scales: tidal, weather events, ENSO, regime shifts, and anthropogenic climate trends. Critical life history stages in estuarine bivalves are temperature-dependent and at risk from ocean acidification. However, few field data are available to test whether organisms have already responded to these environmental changes. Pacific oysters (Crassostrea gigas) were introduced to Willapa Bay, Washington, for aquaculture in 1929 and since that time demonstrated large interannual recruitment variability, including levels considered commercial failures since 2005. Using data sets collected since the 1940s, we examined spawning, larval survival, and recruitment of Pacific oysters and related life history transitions to water temperature and pH.

Results/Conclusions The timing of oyster recruitment accelerated by 4 days per decade, and this advance in phenology aligned with warming trends. In contrast, the magnitude of oyster recruitment was not correlated to mean values of either water temperature or pH. Low-recruitment years exhibited at least one of three weak links: small spawn; poor survival throughout the 3-week larval development period; or poor survival over a short period of larval development. Overall, larval mortality rates varied from -0.12 to -0.34 d^-1 with no clear temporal trend. Nevertheless, high mortality rates were often associated with temperature variability, pointing to the role of weather events, not only climate trends, in near-term forecasts relevant to both biological invasions and sustainable food production.