Graduate Thesis Or Dissertation
 

Calanoid copepod diet in an upwelling system : phagotrophic protists vs. phytoplankton

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  • Calanoid copepod diet was investigated in Oregon coastal waters to determine the trophic significance of phagotrophic protists as copepod prey within an ecosystem where the microplankton biomass is typically dominated by large diatoms. Prior to and during the 1991 upwelling season, clearance rates on phytoplankton and phagotrophic ciliates were measured for Calanus pacificus, Centropages abdominalis, Acartia ion giremis and Pseudocalanus sp.. During the 1992 upwelling season, clearance rates were measured for Calanus marshailae and Pseudocaianus sp. on phytoplankton and both phagotrophic ciliates and dinoflagellates. Copepods cleared ciliates at higher mean rates than they cleared phytoplankton during both years, whereas dinoflagellates were cleared at similar rates to phytoplankton in 1992. C. marshaliae cleared large ciliates at higher rates than equivalently sized diatoms in the midst of diatom bloom conditions, suggesting that C. marshaliae may select ciliates over diatoms. Phagotrophic protists typically comprised <3% of the carbon ingested by copepods during diatom blooms, but 16 to 100% between upwelling induced bloom events and during winter months. Ingestion of ciliates alone provided enough carbon to meet the basic respiration requirements of copepods in the winter of 1991. Copepods are estimated to graze 50 to 100% of the phagotrophic protist biomass per day, thus linking protist production to the carbon flux from surface waters. The lipid content of Calanus pacificus CV's fed diets of diatoms vs. phagotrophic protists was investigated in the laboratory during their maturation process. Dietary inclusion of ciliates and dinoflagellates did not enhance the lipid content or affect the lipid class composition of male copepods. Both diatom and dinoflagellate diets supported a similar level of lipid in the females, whereas females fed diets of ciliates had significantly lower levels of total lipid and no measurable wax ester. The ratio of neutral to phospholipid (WE+TAG / PL) was >1 for males and <1 for females for all treatments. The results of this preliminary lipid study suggest the question of copepod lipid enhancement via dietary inclusion of protists should be addressed at the level of specific fatty acids rather than lipid class.
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