Aquatic bacterial production is incorporated into the food chain through the microbial loop, and the efficiency of the transfer is usually considered dependent on that of the nanoflagellate grazers. Many factors can influence grazing performance in nature, one being the presence of clay particles in the water. During a study of the importance of clay-organic matter aggregates, we found that aggregates are colonized by bacteria (80-90), and few bacteria remain free (20-10) in the water (Davalos-Lind Lind 2001). In many cases the size of the bacteria-colonized aggregate equals phytoplankton cell size. If the size of the bacteria-colonized aggregate facilitates bacteria grazing by macrozooplankton and/or fish, the efficiency of energy transfer in the food web is increased and could represent an additional food source in clay-turbid ecosystems. In clay-rich Lake Chapala we previously demonstrated that native small Atherinids as well as macrozooplankton were capable of consuming clay-organic matter-bacteria aggregates (Davalos-Lind et al. 1992). Others have described methods of fish-grazing on bacteria; thus, our question is, do fish and/or zooplankton significantly impact bacterioplankton in clay-free water as well as clay-rich water? In this paper we study grazing in the presence of clay aggregates and fish grazing in the absence of clays.
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