Date of Completion

Spring 5-1-2013

Thesis Advisor(s)

Eric T. Schultz

Honors Major

Ecology and Evolutionary Biology

Abstract

Despite numerous studies of the ecological effects of the zebra mussel (Dreissena polymorpha) invasion in the Hudson River Estuary, the impacts on larval and juvenile fishes have been poorly characterized. In this study, changes in early life stage fish diets upon invasion of the zebra mussel were analyzed, focusing on the striped bass (Morone saxatilis) and river herring (Alosa pseudoharengus and A. aestivalis). Changes in prey diversity, frequency of prevalent prey items, and a prey habitat index from 1988, before the mussels arrived, to 2008 were quantified. Sample years bracketed a period of increasing mussel impacts, followed by a period of apparent ecosystem recovery. For the striped bass diet, species number doubled and the frequency of prevalent prey items increased up to four-fold during peak invasion years. Both then declined in 2008. Over time, striped bass fed increasingly on benthic prey rather than pelagic prey. Species number for river herring remained relatively constant over time, and they maintained a diet that consisted almost exclusively of pelagic prey. The frequency of some prevalent prey items in the river herring diet increased, others declined, and others exhibited no statistically significant change throughout the study period. After they arrived, zebra mussels became one of the main components of the striped bass diet, but they were never eaten by the river herring. Overall, the zebra mussel has changed many aspects of the striped bass diet, while river herring have attempted to maintain the same dietary structure that they had before the invasion began.

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