SREL Reprint #3400

Fish predation and macroinvertebrate abundance on snags in low-gradient blackwater streams

James A. Lovell1,2, Dean E. Fletcher1, Scott D. Cooper2, and J Vaun McArthur1

1Savannah River Ecology Laboratory, Drawer E, Aiken, South Carolina 29802 USA
2Department of Ecology, Evolution, and Marine Biology, University of California,
Santa Barbara, California USA 93106

Abstract: Investigations into how fish affect macroinvertebrates in lotic ecosystems have produced equivocal results, and few researchers have examined fish effects on invertebrates in sandy-bottomed blackwater streams. We measured the responses of macroinvertebrate density, biomass, and body size to varying levels of fish predation on snags in 2 southeastern USA blackwater streams. We manipulated fish densities in 3 large enclosures (46–64m2) in each of 2 streams and included treatments without fish (0X = control), with fish at ambient density (1X), and with fish at 2x ambient density (2X). Macroinvertebrates in enclosures were sampled using 20 tag alder (Alnus serrulatus) snags, ½ of which were allowed to colonize for 2 wk (colonizing community) and ½ for 2 mo (established community). Increasing invertivorous fish biomass resulted in a significant decrease in total macroinvertebrate density, but not macroinvertebrate biomass, in both types of communities (colonizing and established). We found that the biomass of invertivorous fish was a better predictor of prey responses to manipulations than total fish biomass or density. We conclude that high fish levels can significantly reduce the density of macroinvertebrate prey in southeastern blackwater streams. We attribute this effect to prey vulnerability to a diverse assemblage of stream fishes that prey selectively on small invertebrates.

Keywords: fish predation, macroinvertebrates, blackwater streams, snags, sandy-bottomed

SREL Reprint #3400

Lovell, J. A., D. E. Fletcher, S. D. Cooper, and J. V. McArthur. 2017. Fish predation and macroinvertebrate abundance on snags in low-gradient blackwater streams. Freshwater Science 36(3): 626-634.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).