Stable isotopes of carbon and nitrogen as indicators of diet and trophic structure of the fish community in a shallow hypereutrophic lake

摘要

Stable carbon (delta~(13)C) and nitrogen (delta~(15)N) isotopes were employed to elucidate energy flows and trophic interactions in Lake Apopka, a hypereutrophic lake in central Florida, U.S.A. Isotope compositions oflake biota ranged from —27-1 to — 3-0 per thousand for delta~(13)C, and from 3-7 to 13-9 per thousand for delta~(15)N. The food web was based primarily on plankton production with diatoms, Microcystis and zooplankton dominating the diet of fish. Carbon isotope evidence showed that pico- and nano-phytoplankton were not a direct carbon source for fish, but were important to zooplankton. delta~(15)N mass balance estimates indicated that planktivorous fish obtained 48-85% of their diets from zooplankton. The approx 3 per thousand range ofdelta~(15)N in gizzard shad reflected increasing dependence on zooplankton as fish grew whereas the positive relationship between total length and delta~(15)N of largemouth bass reflected increasing predation on larger planktivorous fish with growth. The broad ranges of delta~(13)C ( - 25-9 to - 9-5 per thousnad) and delta~(15)N (5-8 to 14-4 per thousand) of blue tilapia were indicators of diet diversity. Two presumed omnivores (brown bullhead and white catfish) and piscivores (black crappie, largemouth bass and Florida gar) were found to depend on planktivorous fish. However, stable isotope data revealed no trophic links between blue tilapia, an abundant fish in the near-shore area, and piscivores.