Motile Epifauna of Marine Macrophytes in the Indian River Lagoon, Florida.

I. Comparisons Among Three Species of Seagrasses from Adjacent Beds

A newly-designed sampler was used to quantitatively sample the epifauna associated with three morphologically distinct seagrasses occurring in adjacent beds within 60 m of each other: Thalassia testudinum, Halodule wrightii, and Syringodium filiforme. Similar suites of epifaunal species occurred on all three seagrass species, with a mean of 82% of the species in common; relative abundance, however, differed greatly. All of the top 11 species had significant differences in abundance when standardized to (1) bottom surface area, (2) plant biomass, or (3) plant surface area. Total epifaunal density and gastropod density (per m² of bottom) were greatest on Halodule, while crustacean density was greatest on Thalassia. However, per plant biomass and especially per plant surface area, crustaceans were by far most abundant on Syringodium, despite Syringodium's low biomass and low surface area-to-biomass ratio. Although considered true in previous studies, neither plant biomass nor plant surface area was a good predictor of patterns of epifaunal abundance. Differential survivorship and active habitat selectivity, in combination with seagrass species composition, are probably also important.