is discovered. By combining ^"^C determinations with other tracers of modem particle input 

 (excess ^^^Pb and weapons-fallout) historical variations in carbon accumulation can be 

 assessed. 



The ^''C signature in the different size classes also can be used to assess the relative 

 average ages of organic carbon, and to provide information on the sources of carbon (e.g. 

 carbon fixed on the shelf vs. older oceanic carbon). Other biomarker compounds, such as 

 lignin, are unambiguous source indicators which can provide estimates of contributions by 

 terrestrial carbon. 



F. Consumer Biomass Production and Grazing 



In the water column, these studies can be divided convenientiy into studies of proto- and 

 metazoan zooplankton. Each of these requires different sampling and measurement techniques. 

 In the sediments, studies of biomass production by consumers must include macrobenthic 

 organisms in addition to protozoans and metazoans. 



The overall goal of the protozooplankton studies (specifically phagotrophic flagellates and 

 ciliates < 200 |im in size) is to assess grazing impact of protozooplankton on picoplankton and 

 nanoplankton- sized prey, including heterotrophic bacteria, coccoid cyanobacteria, and < 20 |J,m 

 algal cells. A large part of this research will involve development and testing of new methods 

 of determining protists grazing on various types of prey, and comparing the new methods with 

 more established techniques. Seawater dilution and size fractionation techniques wUl be used 

 to measure rates of protozooplankton growth and grazing. A state-of-the-art color imaging 

 system as well as direct microscopic techniques will be used to identify and enumerate the 

 various components of the protozooplankton community, and determine their carbon biomass. 

 To better couple the above taxonomic and rate process approaches to protozooplankton 

 research, HPLC separation of phytoplankton pigments wUl be used in conjunction with the 

 seawater dilution technique and microscopic examination of the protozooplankton community. 

 Using this approach community functional response curves (i.e. grazing pressure as a function 

 of phytoplankton concentration) will be obtained for individual phytoplankton taxa, and this 

 information will be coupled with data on grazer community composition. 



The goal is to develop a predictive capability concerning the potential grazing impact of 

 individual taxa, and biomass levels of protozooplankton. Current techniques for the 

 measurement of protozooplankton grazing are labor-intensive and generally require lengthy 

 incubations. Thus, developing a predictive capability is critical to overcoming the difficulty of 

 obtaining synoptic measurements of protozooplankton grazing over a sizeable geographic area. 



Methods in development include quantitative measurements of the rates of substrate 

 hydrolysis by a suite of phagotrophic protistan digestive enzymes which relate to in situ rates 

 of bacterivory and herbivory. The suite currentiy includes acid lysozyme (an indicator of 

 bacterivory) and a- and b-glucosidases (indicators of herbivory). The assays can be performed 

 as cell-free assays for determination of community-level fluxes and as intracellular assays for 

 determination of specific trophic pathways. 



Metazoan zooplankton are a major link between primary production and large-bodied 

 predators and the main producers of fecal material that setties to the seabed. To quantify the 

 transformation of carbon by these grazers, we must specify both their biomass, its fluctuation 

 in response to physical forcing, and the rates at which they process carbon. The biomass of 



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