The distributional history and ecology of mangrove vegetation along the northern Gulf of Mexico coastal region.

Historical records and geologic evidence indicate that mangrove populations of the northern Gulf of Mexico region have varied considerably in abundance and species composition since at least the early Tertiary, principally as the result of global, regional and local climatic fluctuations. Recent isozymal and temperature tolerance research has revealed genetic variation between eastern and western Gulf and Caribbean populations of black mangrove and latitudinal ecotypic variations suggesting that an apparent Pleistocene extirpation of mangroves from the northern Gulf region may have caused genetic isolation of east-west populations and a mechanism for natural selection of latitudinal adaptive gradients during post-Pleistocene recolonization. The black mangroves of the coast of Texas have in the last century experienced populational declines and expansions primarily due to localized climatic extremes. During the last decade, black mangrove populations have rapidly expanded in Texas as a result of generally mild, mesic climatic conditions. However, in December of 1983, an extended period of extreme subfreezing temperatures caused an estimated 80 to 85 percent mortality in Texas mangrove populations. The surviving plants, from Galveston to the Rio Grande, in 1985 consist of very low stature individuals comprised mostly of recently (1984) germinated propagules and a few remnant, basally-sprouted older plants.