ABSTRACT
Introduction The most frequently encountered biotopes in the shallow-water areas of the South Florida Bight, Florida Keys, and Florida Bay are the sea grass beds. These marine angiosperms cover around 75% of the open, shallow, soft-sediment seafloors and create a set of habitats that harbor some of the richest molluscan faunules found in southern Florida. Composed of three genera of sea grasses-Thalassia (Turtle Grass), Halodule (Shoal Grass), and Syringodium (Manatee Grass)—the grass beds often completely carpet the seafloor, forming densely intertwined mats of rhizomes. These root mats provide shelter for a speciesrich assemblage dominated by shallowly burrowing bivalves. The three sea grass genera segregate themselves by bathymetry, with Halodule preferring intertidal mud flats and Thalassia and Syringodium preferring deeper-water areas (1-to 10-m depths, depending on water clarity). Because of these bathymetric differences, two different molluscan assemblages occur in the Vegetated Softbottom Macrohabitat: the Bulla occidentalis Assemblage (intertidal Halodule beds) and the Modulus calusa Assemblage (deeper-water Thalassia beds). As between all the biotopes covered in this book, these two main habitat types interfinger and often blur together in broad ecotonal transition zones.
