PARENT SESSION
Tuesday, August 8, 1:30-5:00 pm
COS 43 - Aquatic ecology III: lake ecosystems
Mississippi, Mezzanine Level, Cook Convention Center
Presiders: O Sarnelle

Mass balance approach to modeling a trophic gradient before and after zebra mussel invasion.

Hoyer, Erik^*,1, DeStasio, Bart¹, Reed, Tara², ¹ Lawrence University, Appleton, Wisconsin² Unniversity of Wisconsin - Green Bay, Green Bay, Wisconsin

ABSTRACT- Food web comparisons were made in the Green Bay ecosystem before and after the invasion of zebra mussels (Dreissena polymorpha ). This system exists along a trophic gradient. We analyzed stations in the eutrophic lower bay and mesotrophic middle bay. Chlorophyll levels increased in the middle bay, while they remained comparable to pre-invasion levels in the lower bay. In the lower bay, the phytoplankton biomass was similar before and after invasion. The zooplankton community saw an increase in zooplankton biovolume, with an increasing proportion of that biovolume as Daphnia spp., particularly Daphnia pulicaria . The benthic community of the lower bay remained dominated by Oligochaetes, while the proportion of nematodes in the benthos increased substantially in the middle bay. Numbers of fish in both the lower and middle bay decreased while fish wet mass increased. In the lower bay, the total number of fish declined by 37.5%, while the mass of the fish community increased 32%, probably due to a substantial decline in YOY present in the lower bay. In the middle bay, benthivorous fish increased from 10% to 85% of the fish population and from 2% to 36.9% of the fish biomass. This analysis is a starting point for an integrated food web comparison of the bay before and after invasion. We are currently collecting biomass abundance and transfer rate measurements for multiple trophic levels in the bay. The data we collect is being used to construct an Ecosim/Ecopath model of this system.

Key words: aquatic food web, zebra mussel, mass balance