Nekton use of Macrophyte Patches following Mortality of Turtlegrass, Thalassia Testudinum, in Shallow Waters of Florida Bay (Florida, USA)
Abstract:Widespread seagrass mortality in western Florida Bay has led to increased habitat heterogeneity: once-dominant Thalassia testudinum beds have become punctuated by mud, algae, and Halodule wrightii patches. We tested the hypothesis that increased habitat heterogeneity leads to increased secondary production and diversity. Nekton densities in shallow (depths <1 m) Thalassia meadows and in mud, algae, and Halodule patches were compared 12 times over 3 yrs using a quantitative 2.6 m2 drop trap. Mean densities of fishes and decapods were usually significantly higher in Thalassia beds than in Halodule, algae, and mud patches. The reverse was true for species diversity and richness, which were usually significantly lower in Thalassia beds than in one or more patch types. Macrofaunal densities and species richness and diversity were usually not affected by site (two areas 15 km apart) or time (day vs. night). Six species comprised 84-99% of all organisms in each floral type. Mean densities of Lucania parva, Opsanus beta, and Thor floridanus were almost always significantly higher in Thalassia beds than in Halodule, algae or mud patches. The opposite was true for mean densities of Floridichthys carpio, which were usually significantly lower in Thalassia than elsewhere. Mean densities of Penaeus duorarum were irregularly related to plant type, and those of Gobiosoma robustum were never related to plant type. Time of collection did not affect densities of any dominant species, but mean densities of Thor and Floridichthys were significantly higher on Ninemile Bank than on Sandy Key Bank. Lower nekton standing crops and increased species richness and diversity at the local scale may lead to system-wide faunal changes. However, fisheries seem not to have been affected by seagrass mortality and associated changes in habitat heterogeneity and the forage base.
Document Type: Research Article
Publication date: November 1, 1997
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