ENVIRONMENTAL CONTROLS ON THE DISTRIBUTION OF MODERN BENTHIC FORAMINIFERA IN THE FLORIDA EVERGLADES FOR THEIR USE AS PALEOENVIRONMENTAL INDICATORS

This study examined the environmental factors that control the distribution of modern foraminiferal assemblages in the Everglades in order to provide baseline data for a paleoenvironmental study. Total assemblages from the surface 2 cm of 30 sites across the marsh and mangrove environments of southwest Florida were investigated. Seven environmental variables, including average salinity, salinity range, pH, total phosphorus, and dissolved oxygen, and total organic carbon and total inorganic carbon measured on bulk sediments, as well as the distance from the coastline and elevation were determined for each of the 30 sampling locations. Typically, mangrove swamps are characterized by high-acidity conditions that result in the dissolution of calcareous tests. However, because of the underlying limestone bedrock of the Everglades, the sediment composition is mainly calcium carbonate in the form of fine mud and shelly material, creating a carbonate buffered environment that instead allows for an exceptional preservation of calcareous taxa. Consequently, this enables a more comprehensive understanding of species distribution.

In total, 82 species were identified, the majority of which were calcareous. Diversity decreases, dominance increases, and agglutinated taxa increase from the coastline inland. Rotaliina are equally abundant across the intertidal environment, whereas Miliolina are common near the coast and in lagoons or inland lakes. The most important factors controlling foraminiferal distribution are salinity, and total organic carbon and total inorganic carbon. Jadammina macrescens, Tiphotrocha comprimata, Trochammina inflata, Trochamminita salsa, and Miliammina fusca indicate lower salinities (<18 psu). Good indicators for higher salinities are Haplophragmoides wilberti (16–18 psu) and Arenoparrella mexicana (16–18 psu and 28–30 psu). Ammonia spp. prefer salinities >15 psu and Elphidium spp. >20 psu. Ammonia tepida, Helenina anderseni, Trochammina inflata, and Arenoparrella mexicana prefer organic-rich sediments. Thus, the benthic foraminifera from Everglades sediments are excellent salinity proxies and can be used to determine the history of habitat change in this area, as well as to assess past trends in the rate of sea level rise.