Indirect and direct effects of fish herbivory on nitrogen cycling in nearshore Lake Tanganyika Student: Brittany Graham Mentor: Peter McInytre

When external loading is small, as it is in Lake Tanganyika, the internal redistribution of nutrients can be important for ecosystem productivity. One conduit for this redistribution is fish. Research has been conducted on the transfer of nutrients into the pelagic or benthic ecosystems by benthic or pelagic fishes, respectively, but less attention has been paid to the recycling of nutrients by herbivorous fish in the littoral zone of lake ecosystems. In fact, many researchers have suggested that nutrient redistribution, or recycling of nutrients by fish, plays a small role in the overall nutrient budget of lentic ecosystems. However, in Lake Tanganyika, where the density of herbivorous fish is comparable to coral reef ecosystems, the effect of fish on recycling of nutrients should be more closely examined. Many factors can affect productivity in the nearshore environment, but the main objective of this research was to examine the effects of fish on nitrogen cycling in periphyton. More specifically, I examined (1) uptake of simulated fish excretion (i.e. NH 4 ) by plankton and periphyton communities and (2) the nitrogen turnover rate in periphyton protected and exposed to fish grazing in the littoral zone of Lake Tanganyika.