Influence of macrophyte-induced hypoxia on fish communities in lakes with altered hydrology

Abstract

Altered flow regimes in lakes can change macrophyte habitats from dynamic, species-rich communities to dense, monotypic communities that can change the physicochemical environment available to fish. We tested whether fish community composition, fish density, fish species richness, and fish species diversity changed across a range of dissolved oxygen concentrations (DO; mg/L) in dense stands of several macrophyte species that are commonly the target of macrophyte control efforts in Florida lakes. We sampled fish communities within growths of 5 emergent macrophyte species including cattail (Typha spp.), pickerelweed (Pontedaria cordata), smartweed (Polygonum spp.), torpedograss (Panicum repens), and water primrose (Ludwigia spp.) at lakes Kissimmee and Istokpoga, Florida. Fish communities were sampled using 3 different enclosure gears treated with rotenone, and DO was measured in mid-water column at each site. Macrophyte biomass and DO concentrations were inversely related. Poeciliids accounted for 90% of the catch composition, and density was inversely related to DO. Centrarchid, cyprinodontid, and sport fish densities were highest at DO >4 mg/L. Restoration efforts should reduce dense emergent macrophyte biomass to reestablish habitats with greater habitat heterogeneity, which will increase DO concentrations. These efforts should increase fish species diversity, fish species richness, and improve recreational fisheries in lakes with stabilized water levels.