Seagrass growth and survivorship under the influence of epiphyte grazers

Abstract

Substantial reduction of epiphyte biomass by grazing epifauna is widespread in seagrass systems, and a hypothesized effect is enhanced vigour of the host seagrasses. Effects of epiphyte grazing on seagrass growth and biomass were tested using cultures of the sub-tropical seagrass Halodule wrightii Aschers. established with and without the epiphyte-grazing fauna of local seagrass beds of the Indian River Lagoon, Florida, U.S.A. In the absence of grazing epifauna, a rapid build-up of epiphytes on seagrass leaves occurred and, initially, leaf defoliation was high. After 2 months there was a reduction in growth rate of Halodule in the ungrazed treatment relative to the grazed treatment. Leaf biomass-to-length ratios and shoot biomass were also lower. After 3 months, above-and below-ground biomass and shoot density of ungrazed seagrass were significantly lower, and a substantial drop in productivity had occurred. Results suggest that the suppression of epiphyte biomass by grazing epifauna may be an important factor in the maintenance of growth, productivity and depth distribution of seagrasses, particularly in light-stressed and nutrient-stressed situations.