BIODIVERSITY OF SALINE AND BRACKISH MARSHES OF THE INDIAN RIVER LAGOON: HISTORIC AND CURRENT PATTERNS

摘要

The Indian River Lagoon (IRL) crosses a zone of climatic transition. Historically, marshes dominated saline and brackish environments in the north of the lagoon, while mangroves were dominant to the south. Periodic freezes limited mangrove distribution and abundance. A unique feature of most IRL marshes was seasonal and wind-driven tidal inundation rather than daily tidal fluctuations; near inlets, tidally influenced marshes occurred. Distribution of marsh communities was influenced by hydrology, salinity, soil characteristics, and fire, as well as periodic freezes. Major marsh community types included cabbage palm (Sabal palmetto) savanna, sand cordgrass (Spartina bakeri) marsh, black rush (Juncus roemerianus) marsh, saltgrass marsh (Distichlis spicata, Paspalum distichum), and mixed halophyte (Batis maritima, Salicornia virginica) marsh. Mud flats occupied significant areas. Black (Avicennia germinans) and white (Languncularia racemosa) mangroves occurred in some areas in open to dense stands associated with saltgrasses and mixed halophytes. Red mangroves (Rhizo-phora mangle) apparently occurred as scattered individuals fringing the lagoon. Many of these communities were marked by a few dominant species and relatively low within-community plant species diversity. The resulting landscape pattern was complex and diverse. Marshes of the Indian River Lagoon have been greatly modified since the 1940s. Impoundment or ditching for mosquito control has affected most areas. Much of the low marsh was replaced by open water or by extensive cattail {Typha cf. domingensis) marshes. Loss of connection with the uplands and changed hydrology probably reduced fire frequency and intensity in the high marshes, favoring invasion by wetland shrubs (Salix caroliniana, Myrica cerifera, Baccharis spp.) and the exotic Brazilian pepper (Schinus terebinthifolius). Other impacts to marshes include dredging and filling and nutrient enrichment. Dominant and characteristic plant species of these saline and brackish marshes are widespread throughout the Indian River Lagoon. Few rare plants are associated with Indian River Lagoon marshes. Despite significant modifications, marsh plant species have not been lost from the region, but community and landscape patterns have been greatly modified and ecosystem processes altered. Vertebrates dependent on these marshes have not all faired as well, as evidenced by the extinction of the Dusky Seaside Sparrow (Ammodramus maritimus nigrescens) that depended on marshes of the Indian River Lagoon and the St. Johns River.