MEPS prepress abstract  -  doi: 10.3354/meps07392

ABSTRACT: Submerged aquatic vegetation (SAV) usually hosts higher numbers of both invertebrates and fish than unvegetated substrates. In addition, based on prior laboratory experiments predation risk is thought to decrease with increasing SAV biomass or stem/shoot density, resulting in higher abundance and diversity of potential prey species in dense vegetation. However, all previous tests of the effects of vegetation on prey capture have been similar: constant numbers of predators and prey have been tested at different vegetation densities. Because sampling has repeatedly shown that the abundance of both predators and prey increases with increasing SAV density, an experiment that tests the effects of increasing SAV density on prey capture while also allowing predator and prey numbers to increase would mirror reality more closely than the design of prior experiments. Thus, in laboratory trials we increased the number of predators (pinfish, Lagodon rhomboides (Linnaeus)) and prey (grass shrimp, Palaemonetes pugio Hulthuis) in proportion to increases in SAV shoot density to re-evaluate whether increasing SAV density altered prey survival rates under these more realistic conditions. Treatments included an unvegetated substrate and three different densities (400, 2000 and 4000 leaves m^–2 of artificial SAV (mimicking turtlegrass, Thalassia testudinum Banks and Sol). Our results conflicted with those of prior experiments in showing no significant differences in survival among the different SAV densities (although there was greater grass shrimp survival in SAV than on unvegetated substrate), and indicate that one should not assume that increasing vegetation density will consistently lead to proportionally greater prey survival rates.