A review of environmental conditions along the coastal range of the diamondback terrapin, Malaclemys terrapin

The Diamondback terrapin, Malaclemys terrapin, is distributed along the east coast of North America from Cape Cod, Massachusetts to Corpus Christi Bay, Texas. Six characteristic sections occur along this narrow coastal range, and the individual ranges of the seven subspecies of M. terrapin correspond closely to them. From north to south and west these are the Embayed Section (M. t. terrapin), Sea Island Section (M. t. centrata), Floridian Section (M. t. tequesta in the north, M. t. rhizophorarum in the mangrove thickets of the Florida Keys), East Gulf Coast Section (M. t. macrospilota), Mississippi Alluvial Plain Section (M. t. pileata), and West Gulf Plain Section (M. t. littoralis). Each section is described using the following environmental factors: the underlying geology and geological history, beach conditions, major inflowing rivers, inshore and beach vegetation, ocean currents, tides and wave action, and air and water temperatures. A discussion is presented of the most important of these, in regards to possible influence on subspeciation (geological features and history, environmental temperatures, tidal ranges, and the mangrove vegetation of southern Florida and the Florida Keys). THE Diamondback terrapin, Malaclemys terrapin (Testudines: Emydidae) occupies a narrow North American coastal range that extends from Cape Cod, Massachusetts, to Corpus Christi Bay, Texas, and includes the Florida Keys (Conant and Collins, 1998; Ernst and Bury, 1982; Ernst et al., 1994). It occupies various habitats along the edge of the coastal plain, such as salt marshes, brackish estuaries and lagoons, tidal creeks and flats, and sounds behind barrier islands (Ernst et al., 1994; Palmer and Cordes, 1988). Within this range, seven subspecies are currently recognized (Ernst and Bury, 1982): the Northern diamondback terrapin, Malaclemys terrapin terrapin, ranges along the Atlantic Coast from Cape Cod, Massachusetts to Cape Hatteras, North Carolina; the Carolina diamondback terrapin, M. t. centrata, is found on the Atlantic Coast from Cape Hatteras to northern Florida; the Florida East Coast diamondback terrapin, M t. tequesta, occupies the Atlantic Coast of Florida to the Keys; the Mangrove diamondback terrapin, M. t. rhizophorarum, lives on the Florida Keys; the Ornate diamondback terrapin, M. t. macrospilota, ranges north from Florida Bay in the south along the Gulf Coast to Mobile Bay; the Mississippi diamondback terrapin, M. t. pileata, is found from Mobile Bay west along the Gulf Coast to western Louisiana; and the Texas diamondback terrapin, M. t. littoralis, ranges from western Louisiana to Corpus Christi Bay, Texas. Zones of intergradation occur where the various subspecific ranges meet (Ernst and Bury, 1982; Ernst et al., 1994). It is interesting that the subspecific ranges correspond closely to the six characteristic sections of the North American Coastal Plain described by Thornbury (1965). From north to south and west these are the Embayed Section, Sea Island Section, Floridian Section, East Gulf Coast Section, Mississippi Alluvial Plain Section, and West Gulf Plain Section. The six sections exhibit somewhat different biological, geological and oceanographic characters, which possibly played roles in the evolution of the observed subspecific ranges within M. terrapin.