PRINCIPAL 



INVESTIGATOR(S) Barry F. Sherr and Evelyn B. Sherr 



Both at: College of Oceanography 



Oregon State University 

 Corvallis, OR 97331 



PROJECT TITLE CONTROLS ON MARINE CARBON FLUXES VIA 



PHYTOPLANKTON-MICROZOOPLANKTON 

 INTERACTIONS IN CONTINENTAL SHELF WATER 



AMOUNT OF FUNDING FY 1994: $78 K 



SUMMARY OF GOALS 



The goals of this project were to develop new approaches to assaying protistan grazing 

 on phytoplankton (and on bacteria) in shelf waters. Current approaches for determining in situ 

 microzooplankton grazing rates are in general cumbersome, requiring extensive sample 

 manipulation and fairly long incubation of living organisms. Such methods preclude high- 

 resolution sampling of protist grazing rates. We have spent much of our time on this grant 

 developing exzyme-based assays which will allow increased sampling resolution for protist 

 grazing on bacterial and phytoplankton prey in situ. The Digestive Enzyme Assay (DEA) 

 approach is based on determining the rate of cleavage of a fluorochrome, methylumbelliferyl 

 (MUF) from surrogate substrates at acid (pH 4.5) pH, the pH of protist food vacuoles. The DEA 

 method permits a 'snapshot' of protist digestive enzyme activity and is an in vitro, rather than 

 an in vivo, technique, thus avoiding artifacts associated with manipulation and incubation of live 

 protists. 



SPATIAL AND TEMPORAL SAMPLING SCALES 



The strategy for sampling of protist grazing rates in the OMP program is to obtain data 

 over short time periods within distinct seasons, i.e. intensive sampling during individual cruises. 

 We plan to determine distribution of protistan grazing activity (herbivory and bacterivory) with 

 depth, from inner to outer shelf regions, and between separate transects. 



METHODS AND PLATFORMS 



Our sampling program will require collection of water samples during scheduled cruises 

 in conjunction with the sampling programs of the other biologists. Methods of assessing protist 

 grazing will be: short-term uptake of fluorescently labeled bacteria and acid lysozyme activity 



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