Field evidence of krill grazing on the toxic diatom genus Pseudo-nitzschia in Monterey Bay, California

Both the interactions between toxic phytoplankton and their grazers, and the transport of these toxins through the food chain are relatively poorly understood. Recently, species of the diatom Pseudo-nitzschia have been found to produce the neurotoxin domoic acid, which has caused detrimental effects to higher trophic levels in the food web. One of the key potential vectors for the toxin is the euphausiids (krill). To determine whether krill feed in nature on local species of Pseudo-nitzschia, we compared diatoms in the water to those in the gut of three species of euphausiids in July 1998 during a P pseudodelicatissima bloom and in the gut of one species of euphausiid in August 2000 during a P. australis bloom in Monterey Bay, California. Our findings show that Pseudo-nitzschia was the most abundant diatom in water samples at both times and was also the dominant food in krill. Our findings show that Pseudo-nitzschia was the most abundant diatom in water samples at both times and was also the dominant food in krill, though these diatoms were more common in the diet of resident than in transient species of krill. Thus we demonstrate that krill may be a critical vector in the transmission of domoic acid to organisms at higher trophic levels, including squid, seabirds, and whales, since these predators normally consume krill in Monterey Bay.