Vanni, M. J. Miami University, vannimj@muohio.edu
Headworth, J. J. Miami University, headwojl@miamiu.mohio.edu

 
NUTRIENT RECYCLING AND TRANSPORT BY OMNIVOROUS FISH ALONG A LAKE PRODUCTIVITY GRADIENT
 
Gizzard shad, Dorosoma cepedianum, is an omnivorous, widely distributed fish in eastern US. They consume sediments and plankton. Sediment-feeding gizzard shad consume benthic nutrients and excrete them into pelagic habitats, rendering nutrients available to phytoplankton, thereby functioning as 'nutrient pumps.' Planktivorous shad merely recycle nutrients already in the pelagia. We used a model to explore how gizzard shad abundance, feeding habits, and hence their role in nutrient flux, varies with lake productivity, focusing on reservoirs. Gizzard shad abundance increases dramatically with lake productivity, resulting in density-dependent shifts in feeding behavior. In unproductive lakes (with relatively undisturbed watersheds and low external nutrient loading), shad are relatively scarce and are heavily zooplanktivorous. Therefore they function as nutrient recyclers. In highly productive lakes (with agricultural watersheds and high external nutrient loading), shad dominate fish assemblages. In these lakes macrozooplankton are scarce and shad feed mainly on sediments, functioning as nutrient pumps. Our model suggests that in productive lakes, P supply from gizzard shad can support >40% of pelagic primary production. Thus, the gizzard shad nutrient pump renders productive lakes even more productive. In other words, the gizzard shad nutrient pump may interact synergistically with watershed nutrient inputs to determine realized lake productivity.
 
Day: Tuesday, Feb. 2
Time: 03:30 - 03:45pm
Location: Sweeney Center
 
Code: SS49TU0330S