Where Have All the Acropora Gone? A Review of the Demise of Acropora palmata and Acropora cervicornis Throughout the Caribbean

Out of 150 species of the genus Acropora found in the world, only three are found in the Caribbean and western Atlantic (Veron 1995). These three species are Acropora palmata, Acropora cervicornis, and Acropora prolifera. Acropora palmata has been termed “the most important shallow water coral in the Caribbean and western Atlantic” in terms of reef growth (Hubbard 1997). Additionally, because of its structural complexity, A. cervicornis has also been referred to as “one of the three most important Caribbean corals in terms of its contribution to reef growth and fish and invertebrate habitat” (NOAA 2004). Acropora prolifera is believed to be a hybrid of these two species (Vollmer and Palumbi 2002). The first two aforementioned Acropora spp. have been extremely important in shaping Caribbean and western Atlantic coral reef ecology (hereafter, the author will refer to the Caribbean and western Atlantic as simply the Caribbean). Throughout the Pleistocene and Holocene, the reefs in this region have occurred in an Acropora-dominated zonation (Jackson 1991, 1992; Aronson and Precht 2001). However, in recent decades the ecology of Caribbean and western Atlantic coral reefs has been changed dramatically and, at present, it is generally accepted that these reefs are in crisis (Rogers 1985; Wilkinson 1993; Ginsburg 1994; Eakin et al. 1996; Brown 1997; Connell 1997; Aronson and Precht 2001). As a contributing factor to this crisis over the past thirty years, drastic decline in acroporid coral cover throughout the Caribbeanhas occurred. This is due to mass mortalities on reefs in the region beginning in the late 70’s–early 80’s, namely beginning with a widespread epizootic event of white band disease (WBD) (Antonius 1977; Gladfelter 1982; Weil et al. 2002). Understandably, this has led to loss of habitat and biodiversity on these reefs as well as a reduction in Acropora-dominated reef building (Jackson 1992). After recognizing these significant community changes, many professionals in the scientific and environmental fields have strived to understand the mechanisms of this dieback in order to suggest potential solutions to save these extremely important Caribbeanreef contributors. The State of Floridarecognizes both species to be endangered, but this designation carries no management implications (Deyrup and Franz 1994). Following efforts to gain these lacking management implications, in 1999, A. palmata and A. cervicornis were placed on the candidate list of the Endangered Species Act (Diaz-Soltero 1999), because historical abundance and extent of decline were identified by the National Marine Fisheries Service (NMFS) to be significant enough to warrant such a classification. They are the first corals to be added to such a list in the United States. However, the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) had previously placed blue corals (helioporacea), organ-pipe corals (stolonifera), black corals (antipatharia), and stony corals (scleractinia) including Acropora spp. in their trade regulation agreement. CITES is one of the largest conservation agreements in existence with 160 parties (member countries) to maintain that trade and exploitation of listed species does not threaten their survival. This capstone is relevant to understanding the demise of Acropora. It will address and illustrate the accepted causes for the widespread dieback of A. palmata and A. cervicornis throughout the Caribbean, a region where these two species have been integral contributors to reef-building. This will be achieved by highlighting an overview of what has happened to the two species, including a review of their biology, what is currently being done in terms of their protection, possible causes for their demise, habitat-replacement over geologic time, and hope for the future including current research directions. Acropora prolifera will not be discussed because it is a hybrid of the two, is not as abundant, and has not been as important to reef-building throughout the geologic record