Seagrass epiphyte loads along a nutrient availability gradient, Florida Bay, USA

Abstract

Total epiphyte load, epiphyte chlorophyll load, epiphyte autotrophic index, and seagrass short shoot size are compared with water column nutrient concentrations and the elemental composition of seagrass leaf tissue. The spatial patterns in these parameters are described across a nutrient availability gradient in Florida Bay, Florida, USA. Multivariate and univariate statistical analyses were performed on these parameters to test for correlations with various measures of nutrient availability. Most of the variation in Thalassia testudinum short shoot size could be described by phosphorus availability, dissolved organic matter in the water column, and water column inorganic nitrogen concentrations. Total epiphyte and epiphyte chlorophyll loads were significantly, but weakly, correlated with phosphorus availability. The measurement of total epiphyte loads and observations of epiphytic species composition along a transect adjacent to a point source of nutrients revealed that the effect of nutrient enrichment on epiphyte levels is pronounced but very localized. Epiphyte levels may not be as sensitive to moderate nutrient enrichment as other seagrass parameters (e.g. leaf tissue nutrient content).