Large-scale bloom of Akashiwo sanguinea in the Northern California current system in 2009

Abstract

Significant seabird mortality on the Oregon (OR) and Washington (WA) coast in 2009 has been attributed to a massive bloom of the dinoflagellate Akashiwo sanguinea (K. Hirasaka) G. Hansen & Ø. Moestrup. Initial, albeit limited, observations suggested this bloom began in WA and reached OR waters through southward transport. Here, we explore a combination of remote sensing products and an exceptional latitudinal dataset of plankton counts collected in the surfzone and offshore in OR and WA coastal waters. Records of satellite ocean color for this period support the new finding that blooms were concurrent in OR and WA waters, with no evidence for latitudinal propagation as had been previously suggested. Plankton analyses further indicate that there was a rapid and synchronized increase of A. sanguinea between late August and mid-September of 2009 along wide swaths of the OR and WA coasts. Bloom onset occurred during a prolonged quiescent and warm period in late August–early September, near the end of the March–October upwelling phase. An upwelling event in October likely contributed to foam production through vertical mixing of A. sanguinea rich waters. Bloom intensity peaked earlier and at higher levels in WA waters as compared to OR with cell concentrations exceeding 1.5×106cellsL−1 (WA) and ∼350,000cellsL−1 (OR). In OR samples, A. sanguinea cells comprised upwards of 90% of dinoflagellate cell counts and ∼30% of total phytoplankton cells. At some locations, A. sanguinea persisted well into November–December of 2009, during which time satellite sea surface temperature records indicated anomalously warm surface waters (up to ∼5°C greater than climatological means). Taken together, the data reveal a HAB event of a magnitude unprecedented in over a decade of observations. We hypothesize that these blooms originated from either a cryptic cyst bed and/or a pelagic seed bank of viable vegetative cells.