The effects of vegetation density on the relative growth rates of juvenile pinfish, Lagodon rhomboides (Linneaus), in Big Lagoon, Florida

Abstract

Abstract The efficiency of visual predators may often be affected by complexity of habitat. For example, an increase in complexity of habitat may lead to an increase in search and/or pursuit times, while decreasing habitat complexity may reduce search and/or pursuit times and result in elevated feeding success. If true, it might be expected that predator rates of growth would be greater in small complexity habitats and decline with increasing complexity of habitat. In shallow turtlegrass ( Thalassia testudinum ) meadows, we used field enclosures to evaluate the effect of increasing turtlegrass density (small=0–133 shoots/m 2 , intermediate=177–267 shoots/m 2 , and large=>267 shoots/m 2 ) on the growth rates of juvenile pinfish, Lagodon rhomboides (Linneaus). Experiments were carried out five times during the growing season, with individual experiments lasting from 21 to 28 days. Benthic core samples were taken to examine differences among treatments and possible caging effects on plant surface area, faunal abundance and epiphyte coverage. We found a consistent pattern of decreasing growth with increasing density of vegetation, although due to low power, ANOVA showed no significant differences among treatments. However, the probability of obtaining the same treatment rankings we observed by chance was very low ( P =0.003). The effects of vegetation density on annual growth rates were also examined, and we estimated a 20% decrease in growth rates between small and large vegetation density treatments. These results suggest that vegetation density can have an impact on growth rates that is biologically significant.