NEKTON USE OF MACROPHYTE PATCHES FOLLOWING MORTALITY OF TURTLEGRASS, THALASSIA-TESTUDINUM, IN SHALLOW WATERS OF FLORIDA BAY (FLORIDA, USA)

Widespread seagrass mortality in western Florida Bay has led to increa sed habitat heterogeneity: once-dominant Thalassia testudinum beds hav e become punctuated by mud algae, and Halodule wrightii patches. We te sted the hypothesis that increased habitat heterogeneity leads to incr eased 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 m(2) drop trap. Mean densities of fishes and decapods were usually significantly higher in Thalassia beds than in Halodule, algae, and mud patches. Th e reverse was true for species diversity and richness, which were usua lly significantly lower in Thalassia beds than in one or more patch ty pes. Macrofaunal densities and species richness and diversity were usu ally not affected by site (two areas 15 km apart) or time (day vs, nig ht). Six species comprised 84-99% of all organisms in each floral type . Mean densities of Lucania parva Opsanus beta, and Thor floridanus we re almost always significantly higher in Thalassia beds than in Halodu le, algae or mud patches. The opposite was true for mean densities of Floridichthys carpio, which were usually significantly lower in Thalas sia than elsewhere. Mean densities of Penaeus duorarum were irregularl y related to plant type, and those of Gobiosoma robustum were never re lated to plant type. Time of collection did not affect densities of an y dominant species, but mean densities of Thor and Floridichthys were significantly higher on Ninemile Bank than on Sandy Key Bank. Lower ne kton standing crops and increased species richness and diversity at th e local scale may lead to system-wide faunal changes. However, fisheri es seem not to have been affected by seagrass mortality and associated changes in habitat heterogeneity and the forage base.