The rocky intertidal biota of the Florida Keys: Fifty-two years of change after Stephenson and Stephenson (1950)

A study of the rocky intertidal environments of the Florida Keys by Stephenson and Stephenson (1950) serves as a valuable baseline of littoral communities prior to extensive development and human population pressures. Five of the study areas originally surveyed in 1947 were resurveyed in 1999 to assess any community changes which may have occurred in the intervening 52 yrs. A more extensive sampling effort in 1999 yielded a greater number of taxa as compared to 1947 (120 vs 78). However, one intertidal zone showed a decrease in taxa richness, not all species recorded in 1947 were seen in 1999, and others had shifts in abundance or zones of occurrence. The gray zone at the high mean water mark may have experienced degradation from the deposition of seagrass, debris, or hydrophobic substances as suggested by a 79% decrease in the species that occurred there, despite an increase in the number of species found in all other zones. Harvesting, pollution, or general habitat degradation may explain the complete absence or reduced abundance of some species, particularly those considered as dominant or characteristic intertidal community members in 1947. Increased nearshore eutrophication and/or changes in grazer communities may explain an apparent upward shift of some macroalgal species and the appearance at more heavily developed sites of algal nutrient indicator species (e.g., Cladophora, Chaetomorpha, and Enteromorpha). Our results are consistent with increasing evidence that disturbances, such as eutrophication, are having a negative effect on rocky intertidal communities of the Florida Keys.