A Comparison of Fish Faunas Found in Pure Stands of Two Tropical Atlantic Seagrasses, Thalassia testudiunum and Syringodium filiforme

Abstract

Quantitative samples of fish faunas found in pure stands of Thalassia testudlnum and Syringodium filiforme were taken using ®Pronoxfish. The fish faunas of the two habitats were compared for similarity of species, species diversity, and biomass to assess habitat equivalency of the two seagrass communities. Peter's (1971) method of analysing biogeographic data was used. The resulting cluster analysis using minimum distance showed all within habitat comparisons to cluster within a scalar distance of 99 while between habitat comparisons clustered at a scalar distance of 6.1 indicating that the associated faunas of the two seagrasses are highly dissimilar. Mean fish biomass of samples from Thalassia was 3.15 g/m2 while that of samples from Syringodium was 0.65 g/m2. These values were significantly different (df = 20, t = 5.33, p<.001). Mean diversity (H') of samples from Thalassia was 2.38 and that of samples from Syringodium was 2.11. These values are not significantly different (df = 20, t = 1.26, p>.05). Differences between sea grass fish faunas were obvious both at family and species levels. From these data it seems that the two seagrass types are not equivalent as fish habitats. The reasons for this lack of equivalency probably related to substrate, relatively higher patchiness in the Thalassia habitats, and environmental structure imposed by blade morphology.