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Krill are important grazers on diatoms and critical prey items for many high level carnivores in Monterey Bay and elsewhere along the California coast. Here, some of the higher level consumers have recently been shown to be severely affected by the toxin, domoic acid (DA), a secondary metabolite of some species of the diatom Pseudo-nitzschia. To understand the potential role of krill in vectoring DA from diatoms to large predators, several grazing experiments were conducted. Field-collected Euphausia pacifica and Thysanoessa spinifera were fed on a diet of toxic and non-toxic Pseudo-nitzschia species. Gut evacuation rates of krill and CHN analysis of the algae were obtained concurrently to determine gut residence time and nutritional value of the food. Our results from a short-term (6 h) grazing experiment demonstrated that both E. pacifica and T. spinifera consumed toxic Pseudo-nitzschia multiseries but the responses of the two krill species differed to a degree, with E. pacifica having the higher weight-specific feeding rate. Results from a longer-term (24 h) grazing experiment showed that E. pacifica had a different, interrupted grazing pattern and showed no immediate ill effects when consuming toxic P. multiseries as contrasted with its more constant feeding pattern on non-toxic Pseudo-nitzschia pungens. We show that toxin loads in krill digestive tracts, estimated from feeding rates and gut residence time measured here, match the observed body burdens of DA measured in field-collected krill during toxic blooms. Such data are important for predicting toxin transfer from krill to higher trophic levels during blooms of toxic algae. As an example of this transfer, we show the vulnerability of a krill-feeding seabird, Cassin's Auklet (Ptychoramphus aleuticus) to DA likely vectored by krill during toxic Pseudo-nitzschia blooms.

The Vibrionaceae (Vibrio) are a ubiquitous group of metabolically flexible marine bacteria that play important roles in biogeochemical cycling in the ocean. Despite this versatility, little is known about Vibrio diversity and abundances in upwelling regions. The seasonal dynamics of Vibrio populations was examined by analysis of 16S rRNA genes in Monterey Bay (MB), California from April 2006-April 2008 at two long term monitoring stations, C1 and M2. Vibrio phylotypes within MB were diverse, with subpopulations clustering with several different cultured representatives including Allivibrio spp., Vibrio penaecida, and Vibrio splendidus as well as with many unidentified marine environmental bacterial 16S rRNA gene sequences. Total Vibrio population abundances, as well as abundances of a Vibrio sp. subpopulation (MBAY Vib7) and an Allivibrio sp. subpopulation (MBAY Vib4) were examined in the context of environmental parameters from mooring station and CTD cast data. Total Vibrio populations showed some seasonal variability but greater variability was observed within the two subpopulations. MBAY Vib4 was negatively associated with MB upwelling indices and positively correlated with oceanic season conditions, when upwelling winds relax and warmer surface waters are present in MB. MBAY Vib7 was also negatively associated with upwelling indices and represented a deeper Vibrio sp. population. Correlation patterns suggest that larger oceanographic conditions affect the dynamics of the populations in MB, rather than specific environmental factors. This study is the first to target and describe the diversity and dynamics of these natural populations in MB and demonstrates that these populations shift seasonally within the region. © 2014 Mansergh and Zehr.