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1. Treatment ∆Cells (E5 ml-1) µ (d-1) Control 5.8 0.77 Zero Virus 13 1.7 Grazer 8.9 1.3 The Effects of Trophic Complexity on the Production, Abundance and Community Structure of Bacterioplankton Abstract Aubrey Cano1, Elisa Wallner, Craig Carlson T-RFLP pattern after HAE III digest DOMINOs (Dissolved Organic Matter IN the Ocean) is a multi-institutional project that asks the question: How does varying the release mechanisms of DOM affect the quality and quantity of DOM? The three main release mechanisms include 1) direct release (via phytoplankton exudation) 2) zooplankton release via sloppy feeding and release and 3) viral lysis or prokaryotic and eukarytic cells. In the first field season, we examined the bacterial response to these differing DOM production mechanisms by monitoring changes in bacterial production and community structure shifts. We participated on a Chesapeake Bay cruise in July 2004 looking at DOM produced in the light during a nutrient regeneration dominated time period. We then performed dark remineralization incubations to assess changes in bacterial growth rate, DOM bioavailablity and potential changes in bacterial community structure. 1. UCSB Marine Science Interdepartmental Graduate Program DOM Remineralization in the Dark DOM Production in the Light Figure 4 . Fragment length patterns for initial and final time points of the remineralization experiment. Figure 3. Bacterial abundance derived from varying DOM Produced in the light experiment. Conclusions Direct release and grazer mediated release of DOM had differing effects on bacterial growth rate and community structure. The higher growth rates for the grazer and direct released DOM treatments indicate an increase in bioavailablity to bacteria. The DOM produced by the zero virus (direct release) and control treatments possibly caused an observed shift in bacterial community structure in those treatments. We did not observe significant community structure shift within the grazer treatment; however different restriction enzymes may yield higher resolution. Figure1. Bacterial abundance in the light experiment Table 1. The change in cell numbers during the log phase of growth and growth rate for each treatment in the remineralization dark incubations. Figure 2. Bacterial production in the light experiments.