Diet analysis and community characteristics of Lepomis (sunfish) species congregating near natural spring vents of the Rainbow River, Florida

Michael S. Sears

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science, Department of Environmental Science, Policy, & Geography, College of Arts and Sciences University of South Florida St. Petersburg

Abstract

Little is known about the ecology of natural springs and the influence spring vents have on fish populations. This study explores fish population characteristics, such as abundance, diversity, and length distributions near headwater spring vents and downstream away from the spring vents within the Rainbow River, located in central Florida. The population characteristics examined are useful to resource managers when evaluating the possible impacts on fish populations from increased groundwater withdrawals and subsequent lower discharge rates into large spring-fed rivers. Initial field observations led to the hypothesis that Lepomis species feed on organisms expelled from the spring vents. Electrofishing and hook and line sampling were utilized to collect fish specimens for analysis, and Lepomis species were frozen for later stomach analysis, or stomach contents were pumped in the field. Spotted sunfish (Lepomis punctatus) were dominant upstream (28.8% composition), while bluegills (Lepomis macrochirus) were most abundant downstream (38.0% composition). Upstream populations of Lepomis species had significantly larger individuals (P < 0.05) than Lepomis species sampled downstream. Lepomis species stomach analysis revealed Hyalella azteca as the most abundant food source upstream, and chironomids as the most abundant prey taxa downstream. Upstream Lepomis species stomach analysis yielded an average of 19.05 organisms identified per individual fish, while 4.01 v organisms per fish were observed downstream. These differences in Lepomis species populations and their diets indicate that future groundwater withdrawals could impact these stable state spring environments, and have substantial impacts on the ecology of the Rainbow River.