Increased Nutrient Loading of Spring-fed Coastal Rivers: Effects on Habitat and Faunal Communities
   Tom Frazer, University of Florida

Abstract: The overall goal of our research program is to develop and transfer into management a mechanistic understanding of the ecological effects of nutrient enrichment on Florida’s spring-fed rivers. For this work, we capitalize on an established sampling program in the Chassahowitzka and Homosassa rivers where nutrient and vegetation data have been collected since 1998 (see Frazer et al. 2001 and 2006). This project is intended to provide the complementary invertebrate and fish data essential to achieve the overall goal. Specific objectives for this project are: (1) to characterize quantitatively the invertebrate and fish assemblages in the Chassahowitzka and Homosassa rivers; (2) to provide accurate and precise measures of abundance and biomass for both invertebrates and fishes; and (3) quantify the food habits of the fishes so that trophic relationships can be established. During the second quarter of this effort, we continued processing of invertebrate samples collected during the first quarter of this effort, i.e. August 2007. In addition, quantitative analyses of fish data were completed to estimate the probability of capture, abundance and density for all species recaptured during electrofishing sampling, as well as for fishes that were numerous at seine depletion sites. Fish diet processing and invertebrate analyses are ongoing and are likely to be completed prior to the winter sampling to be carried out in 2008. Preliminary data on invertebrates indicate a general similarity in the assemblages associated with bottom sediments in the two rivers, and also the assemblages associated with submersed aquatic vegetation. The numbers of invertebrates associated with submersed aquatic vegetation, however, is markedly less than the numbers of invertebrates collected from the sediment. With regard to the fishes in the two rivers, capture probabilities varied considerably between species for both gear types, suggesting that it may be important to use species-specific capture probabilities when estimating abundances and densities. Mechanical failure while sampling the Chassahowitzka may have reduced the number of individuals recaptured and future sampling events may produce estimates for a greater number of species. Density estimates for small-bodied species captured in seines show a considerably higher density in the middle reach of the Chassahowitzka River compared to the Homosassa River. Density of small-bodied individuals decreased with transect sampled downstream in the Homosassa River, while density remained relatively high in the upper six sites of the Chassahowitzka. A preliminary estimate of fish biomass by reach was completed using shared probability of capture between species, based on similarity in body-size, and estimated from species that were recaptured or from seine depletion sites. Total fish biomass was lower in reaches 1 and 3 of the Homosassa River compared to the Chassahowitzka River, but was higher in reach 2 due to a high catch of large hardhead catfish in the midstream seine depletion site. While this resulted in an inflated biomass estimate of catfish in the reach, high biomass of catfish was also observed in the middle and lower reaches of the Chassahowitzka River.

Award Matching Funds Total
$262,907.00 $262,907.00 $525,814.00

Year Funded Starting Date Ending Date
2006 6/1/2007 7/31/2011

Location: Citrus County