Population model for the threatened coral, Acropora palmata

by: Tali Vardi

Advisors: Jeremy Jackson and Stuart Sandin

    Acropora palmata, a fast growing coral that relies primarily on asexual reproduction, was once the dominant reef-builder in shallow reef environments throughout the Caribbean. Since the 1980s it has suffered a 97% decline in abundance throughout its range and was Acropora palmata included on the US Endangered Species List in 2006. Despite the dramatic nature of this decline, and the equally dramatic loss of reef habitat that would be caused by an extinction, neither abundance nor rates of decline have been documented systematically throughout the Caribbean.  In Autumn 2007, abundance of A. palmata  was estimated in Florida, Puerto Rico, Jamaica, Virgin Gorda (British   Virgin Islands), and Curaçao. Abundance in Florida was dramatically lower than in other sites. The scarcity of A. palmata in Florida is explained by increased hurricanes and disease, problems that are difficult to manage. 
   
    To explore population changes in more detail a population model was developed for the Florida A. palmata  population. This model utilizes data on the size, birth, and death of individual coral colonies measured four times per year for three years (and ongoing), to estimate changes to the regional population and predict future changes– e.g. abundance of colonies over time. Based on A. palmata’s population trajectory since 2004, the local population density, currently just a remnant of what it once was, will decline an additional 90% in 10 years. Due to a healthy collaboration with NOAA’s Southeast Regional Office, these results will be incorporated into the Recovery Plan for A. palmata.

    Parallel time-series data from Curaçao, Puerto Rico, Virgin Gorda, Navassa, and Jamaica are being collected and analyzed to create similar models for A. palmata populations throughout the Caribbean. So far we see differences in life history traits (e.g. relatively high rates of recruitment in Jamaica, and large adult colonies in Curacao). These differences can help us to understand regional and global decline, and make plans for recovery. We will be able to answer: How fast is each population abundance declining or recovery? Will planting recruits lead to stable population size? If so, how many recruits must we plant? How many recruits are necessary to reach former density levels? Which populations should we save? Those most at risk? Those with signs of recovery?

    Answering these questions is already allowing managers in Florida to choose quantitatively-defensible recovery strategies, e.g. targeted plantings at appropriate sites. Similar benefits will follow to the other regions. Using population dynamic modeling techniques to answer basic questions regarding A. palmata recovery is critical to the persistence of the Caribbean’s shallow reef. Additional funding for this project will help create a more highly resolved image of A. palmata population dynamics throughout the Caribbean. Target sites include Belize – wherein A. palmata seems to be recovering, Panama – which may offer a baseline level of A. palmata abundance, as well as Honduras and Guadeloupe which are data poor.
 
Project Details