Relationships among upwelling, phytoplankton blooms, and phycotoxins in coastal Oregon shellfish

Abstract

Climatologies derived from satellite data (1998 to 2007) were used to elucidate seasonal and latitudinal patterns in winds, sea surface temperature (SST), and chlorophyll concentrations (chl) over the Oregon shelf. These were further used to reveal oceanographic conditions normally associ- ated with harmful algal blooms (HABs) and toxic shellfish events along the Oregon coast. South of 43° N, around Cape Blanco, summer upwelling started earlier and finished later than north of 43° N. Spring blooms occur when light limitation is relieved, before the initiation of upwelling, and sec- ondary, more intense blooms occur approximately 2 wk after upwelling is established. North of 45° N, SST and chl are heavily influenced by the Columbia River plume, which delays upwelling-driven cooling of the surface coastal ocean in spring, and causes phytoplankton blooms (as indicated by increased chl) earlier than expected. The presence of saxitoxin in coastal shellfish, which causes paralytic shellfish poisoning, was generally associated with late summer upwelling. The presence of domoic acid in shellfish, which leads to amnesic shellfish poisoning, was greatest during the transi- tion between upwelling and downwelling regimes. This work demonstrates that satellite data can indicate physical situations when HABs are more likely to occur, thus providing a management tool useful in predicting or monitoring HABs.