| Summary: | Despite the ecological importance of crustacean zooplankton there is little knowledge about how their populations will be affected by ocean acidification. The copepod Calanus pacificus and the krill Euphausia pacifica are two dominant crustacean zooplankton that are important prey species in the food webs of Puget Sound and the North Pacific. We currently observe pCO2 levels of 1600 μatm in bottom waters of several areas of Puget Sound and concentrations of 2400 μatm have been observed in southern Hood Canal. These high CO2 levels are the result of both anthropogenic and natural processes but the temporal and spatial extent of high CO2 waters are expected to expand as atmospheric CO2 concentration increases. In this study we spawned C. pacificus and E. pacifica at different pCO2 levels and monitored their hatching success and development of the early life stages which are likely to be most vulnerable to stress. Our preliminary results show that egg hatching in E. pacifica is robust to increased pCO2 across the range of 400-3200 μatm pCO2. However, the proportion of hatched nauplii that develop to the first feeding stage over seven days is significantly reduced at pCO2 levels of 1600 μatm and greater. Egg hatching in C. pacificus is reduced at 2400 μatm pCO2 while the proportion of nauplii that reach the first feeding stage over four days is reduced, but only at high (3200 μatm) pCO2. Further work on C. pacificus at less extreme pCO2 concentrations is needed to resolve the pCO2 level where hatching begins to be affected. These data suggest that E. pacifica populations may be more vulnerable to ocean acidification than those of C. pacificus and its development is significantly slowed at CO2 concentrations that are currently observed in the bottom waters of Hood Canal. Because development rate significantly affects survival to adult, acidification has the potential to influence krill populations and impact the food webs of the Salish Sea.
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