Chapter 14: Bridging Trophic Levels through Analysis of Biomass Size Spectra in Oneida Lake, New York
Allison E. Gamble, Russell C. Lloyd, Ora E. Johannsson, and Edward L. Mills
The search for suitable biotic indicators of ecosystem change in aquatic ecosystems is of paramount importance to scientists and managers because these ecosystems are impacted by numerous anthropogenic perturbations including invasions by exotics, excessive nutrients, and water quality degradation (Mills et al. 1994; Effler et al. 2001; Vinebrook et al. 2002). Total phosphorus, for example, is a useful indicator as it reflects the degree of eutrophy of an ecosystem and potential algal standing crop (Vollenweider 1968). Body size is also a useful indicator of ecosystem status and a good indicator of predator–prey balance in a trophic food web (Mills and Schiavone 1982; Kerr 1974; Jennings et al. 2002). A common symptom of an imbalance in aquatic ecosystems is the distortion of the expected relationship between the biomass of organisms and body size (Sprules et al. 1983; Kerr and Dickie 2001).
Oneida Lake is an ideal ecosystem to assess indicators of environmental change. The lake and its food web have been impacted by recent biological invasions, reductions in phosphorus, and changes in fish populations. During its recorded history, Oneida Lake has exhibited algal blooms reflective of enriched conditions. Total phosphorus concentrations were reduced from levels of 49.6 (±12.8 μg/L) from 1975 to 1986–28.8 (±7.9 μg/L) between 1987 and 1995 in an effort to reduce the algal blooms in the lake (Idrisi et al. 2001). Zebra mussels Dreissena polymorpha were first identified in 1991, and have been abundant since 1992 (Idrisi et al. 2001; Mayer et al. Chapter 9). The zooplankton community has been dominated by two daphnid species in the early summer, Daphnia pulicaria and Daphnia mendotae, often shifting to smaller-bodied copepods and herbivorous cladocerans in later summer (Mills et al. 1987). The dominant zooplanktivores are young-of-the-year (YOY) fish such as Yellow Perch Perca flavescens and Gizzard Shad Dorosoma cepedianum, both known to be able to collapse the large bodied Daphnia population (Mills and Forney 1983; Roseman et al. 1996; Shepherd and Mills 1996).