Distribution, abundance and domoic acid analysis of the toxic diatom genus Pseudo-nitzschia from the Chesapeake Bay

Very little research has been conducted on mid-Atlantic estuarine populations of the diatom Pseudo-nitzschia despite recent evidence of toxicity in regional isolates. We collected field samples from the Chesapeake Bay region from 2002 to 2007 for Pseudo-nitzschia enumeration and toxin analysis. Abundances of Pseudo-nitzschia were highest in the winter and spring at 10(3) cells ml(-1). Domoic acid (DA) was detectable in 42% of samples tested, but concentrations were generally low, ranging from 0 to 1,037 pg DA ml(-1) (mean 176 pg DA ml(-1)), and DA cell quota ranged from < 0.1 to 49.4 pg DA per cell (mean 1.4 pg DA per cell). Although Pseudo-nitzschia populations were observed year round when salinity was >= 5, populations were highest from February to May when temperatures were low (2-15 degrees C) and salinity relatively high (>= 10). Six species of Pseudo-nitzschia were identified via transmission electron microscopy of the samples: P. pungens (Grunow ex Cleve) Hasle, P. calliantha Lundholm, Moestrup et Hasle, P. subpacifica (Hasle) Hasle, P. cuspidata (Hasle) Hasle emend. Lundholm, Moestrup et Hasle, P. fraudulenta (Cleve) Hasle and P. multiseries (Hasle) Hasle. P. calliantha was the most common and not previously reported from the Chesapeake Bay. Of these species, P. pungens, P. calliantha, P. cuspidata, P. fraudulenta and P. multiseries are known to produce domoic acid.