Alexandrium ecology in Puget Sound: bloom transport and climate pathways

The Puget Sound Alexandrium Harmful Algal Bloom (PS-AHAB: www.tiny.cc/psahab) program 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 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 (see presentation by C. L. Greengrove at this conference). The potential for blooms to initiate from these locations was determined by a series of controlled germination experiments in the laboratory using cysts isolated from benthic sediments. Transport of blooms was evaluated using a high-resolution hydrodynamic simulation of Puget Sound and adjacent coastal waters (MoSSea: http://faculty.washington.edu/pmacc/MoSSea/). Within this model domain, passive particles were released from the seed beds and tracked for 20 days. In two weeks, particles released from Bellingham Bay made it out of the Strait of Juan de Fuca to the outer Washington coast whereas particles released from Quartermaster Harbor mostly stayed in the main basin of Puget Sound. No particles entered Hood Canal, suggesting that physical transport mechanisms may prevent toxic cells from contacting shellfish in this basin of Puget Sound. Laboratory experiments showed that maximal growth rates (~0.3-0.5 μ d-1) occur over a broad range of temperatures (~14-24°C) at salinities (20-35 psu) typical for Puget Sound (see presentation by B. D. Bill at this conference). These ranges were used to define favorable habitat for A. catenella using model output from the MoSSea simulation. A 40-year global climate projection was regionally downscaled and coupled to MoSSea to determine temporal and spatial changes to favorable habitat under the A1B greenhouse gas emissions scenario. A comparison between present-day and circa-2050 conditions allows us disentangle the effects of three climate pathways on favorable habitat for A. catenella in Puget Sound: 1) changing ocean inputs (associated with upwelling winds), 2) changing streamflow magnitude and timing, and 3) increased direct insolation