Alexandrium cyst distribution and germination in Puget Sound

The Puget Sound Alexandrium Harmful Algal Bloom (PS-AHAB: www.tiny.cc/psahab) program, funded by NOAA/ECOHAB, seeks to understand environmental controls on the benthic (cyst) and planktonic life stages of the toxic dinoflagellate Alexandrium catenella, and disentangle the effects of climate pathways on the timing and location of blooms. Spatially detailed mapping of winter surface sediment cyst distributions in 2011, 2012, and 2013 found the highest cyst concentrations in Bellingham Bay in the north and Quartermaster Harbor in central Puget Sound. However, the viability of cysts at these seed bed areas is low – with fewer than 54% of cysts germinating when incubated at favorable temperatures. The time of year that cysts can germinate does not appear to be controlled by an endogenous clock, but the rate of germination is strongly determined by temperature. These results may complicate potential relationships between cyst abundances and bloom magnitude the following season. A monthly time series of cyst abundances was also collected at two locations in Quartermaster Harbor from 2012-2013 as part of a related Sea Grant project investigating the seasonal variability in cyst abundances. Cyst abundances varied by a factor of ~6 with the lowest cyst abundances occurring in the spring (Apr) and the highest cyst abundances occurring in late fall (Oct/Nov). This seasonal pattern is consistent with observed A. catenella bloom dynamics in Quartermaster Harbor. The improved understanding of the processes that govern cyst germination and bloom initiation provided by this study contribute towards the development of a predictive capacity for A. catenella blooms in Puget Sound. Details on A. catenella growth rates and toxicity and an analysis of potential bloom transport using a high-resolution hydrodynamic simulation of Puget Sound and adjacent coastal waters (MoSSea: http://faculty.washington.edu/pmacc/MoSSea/), as well as simulations of potential future climate impacts on blooms, will be discussed in separate presentations by B.D. Bill and S.K. Moore respectively, at this conference