Krill: a potential vector for domoic acid in marine food webs

Over the past decade, blooms of the domoic acid (DA) producing diatom Pseudonitzschia have been responsible for numerous deaths of marine mammals and birds in Monterey Bay, California. Euphausiids (krill) are important members of the local zooplankton grazer community and comprise the primary diet of squid, baleen whales, and many seabirds. Krill are thus a key potential vector for the transfer of DA to higher trophic level organisms in Monterey Bay. A better understanding of the quantitative trophic interactions and body burden of DA in krill is required to predict whether they can act as an effective vector for this neurotoxin. Here we report results of toxin analyses and gut content examinations of krill Euphausia pacifica collected from Monterey Bay in 2000. Corresponding counts of toxic Pseudo-nitzschia species in the water and their cellular DA concentrations were also obtained at the collection sites. Toxin analysis by receptor binding assay demonstrated that DA in krill tissue varied between 0.1 to 44 μg DA equiv. g–1 tissue (confirmed by tandem mass spectrometry), with levels corresponding to the abundance of toxic Pseudo-nitzschia species present in the water. The occurrence of Pseudo-nitzschia australis frustules in the digestive tract of E. pacifica verified that a toxic species of this diatom was an important part of their diet and thus implicated this phytoplankter as the source of DA. These findings provide compelling evidence for the role of krill as a potential transfer agent of the phycotoxin DA to higher trophic levels in marine food web.