Document: JOH-3-75-8

Trophic interactions of large-piscivorous and small-omnivorous fishes in freshwater marshes of the Florida Everglades.

CHICK, J.H.* ¹ and J.C.TREXLER ¹

Florida International University, Miami, FL, 33199, USA ¹
University of Chicago, Chicago, Illinois, 60637 USA ²
University of New Orleans, New Orleans, LA, 70148, USA ³

Abstract:
Two important features of freshwater marshes in the Everglades have not been thoroughly researched. First, a lack of information about large-piscivorous fishes has led to dichotomous descriptions of their importance, from suggestions that they control population growth of small fishes to suggestions that they are too rare to be ecologically important. Second, Everglades marshes support an unusually large standing stock of periphyton, often manifested in a calcareous floating mat. Interactions between grazers and periphyton are complex because nutrient regeneration by omnivores can stimulates algal growth and physical features of mature periphyton mats can impede grazing. We conducted caging experiments to clarify the role of large-piscivorous and small-omnivorous fishes in the Everglades food web. Closed treatments demonstrated that mosquitofish, the numerically dominant small-omnivorous fish, significantly reduced recruitment of macroinvertebrates, but had no significant net effects on periphyton. We also used open and refuge treatments to examine effects of large-piscivorous fishes, and found significantly greater use of the refuge treatment by small fishes, amphibians, and macroinvertebrates. Greater abundance of grazers in the refuge treatment significantly reduced new growth of epiphytic algae, but did not affect mature periphyton mats. Our experiments suggest large fishes in the Everglades may be abundant enough to at least influence habitat selection by prey taxa. Additionally, patterns of grazer effects suggest physical features of mature periphyton mats that impede grazing may be critical to food web interactions in this system.

Keywords: Trophic interactions, freshwater marshes, large-piscivorous fishes, small-omnivorous fishes, periphyton, Florida Everglades

This abstract is being presented at: 2:15 PM in session:
Oral Session #11: Trophic Cascades.