Environmental conditions associated with domoic acid in razor clams on the Washington coast

In October 1998, record levels of the neurotoxin domoic acid (DA) were detected in razor clams (Siliqua patula, Dixon) resulting in the closure of shellfish harvesting areas along the Washington coast. This toxin was detected in seawater samples collected at Kalaloch Beach and Second Beach on the central Washington coast using a receptor binding assay and liquid chromatography tandem mass spectroscopy. Domoic acid levels ranging from 0-2700 ng/L were measured in seawater samples containing from 70-100% Pseudo-nitzschia pseudodelicatissima (Hasle) Hasle at concentrations of 1.0-15 x 10(6) cells/L, resulting in maximum levels of cellular toxin of approximately 500 fg/cell. A cultured isolate of this species collected from Kalaloch Beach also produced DA, as determined by the receptor binding assay, during late exponential and stationary stages of growth. The toxic P. pseudodelicatissima bloom in the late summer and autumn of 1998 occurred 2-3 weeks after strong coastal upwelling during a period of anomalously low rainfall, typical in post-el Nino years. Higher toxin levels in seawater at Kalaloch Beach compared to Second Beach were attributed to the periodic nature of upwelling at Kalaloch Bench, demonstrated by a 175-fold increase in nitrate in seawater coincident with a 5 OC decrease in sea sui face temperature on September 1. The upwelling event in September was followed by wind relaxation and reversal at the end of that month, resulting in the transport of toxic cells toward the coast where nutrients were already present to fuel the algal bloom. A pulse of nutrients, either from rainfall or upwelling, to coastal regions that have experienced several weeks of low nutrients, followed by wind relaxation or reversal events that transport cells to inshore regions, are suggested to be important factors in the initiation of the most toxic Pseudo-nitzschia species blooms on the Washington coast.