A Study of Population Dynamics of Scleractinians on Conch Reef: A Demographic and Population Genetics Approach.
Principal Investigator: Mary Alice Coffroth, SUNY-Buffalo

A major goal in ecology is to understand factors that affect the distribution and abundance of species species, and mechanisms that drive changes in community structure. Knowledge of this sort is especially needed in coral reef communities where substantial decreases in coral cover and changes in coral species composition have occurred over the past few decades.

Many different processes affect changes in coral cover and species composition, such as recruitment, herbivore, and competition. Scientists who study these processes rely on coral reef monitoring programs to detect and describe changes that occur on individual reefs, and throughout regions. Most coral reef monitoring programs focus primarily on estimates of percent coral cover and diversity, but to fully understand community and population dynamics information is needed about population structure. This includes such factors as the source of new individuals to a population (recruits), and the age and size structure of individuals that make up coral populations on the reef. Much as the United States government takes a census of our population every ten years, reef scientists are beginning to use similar techniques to describe changes in coral populations. Recruitment, for example, is equivalent to births and is an important indicator of a reef's regeneration or growth potential. Recruitment is influenced by adults from local and distant communities, local oceanography because many coral larvae drift in the plankton before settling down as juveniles, the complexity of bottom types found on reefs, and grazing intensity.

An important question related to coral recruitment (especially from conservation considerations) is "where do new recruits come from?" Are the recruits immigrants from distant reefs or are they supplied locally? Depending on the source of the larvae, local community and population dynamics can have a profound effect on recruitment patterns. For example, if recruits are continuously supplied from distant "upstream" areas, then the consequences of local disturbance (such as from pollution, ship groundings, or other processes that kill parent colonies) on communities may not be great. If, however, recruits are largely derived locally, then processes that lead to a reduced abundance of reproductive adults can ultimately lead to a decline in the population.

There are few studies that examine this aspect of coral population dynamics on a local scale, on a single reef. In this study Aquarius will be used to examine the influence of recruitment on the species composition of corals at Conch Reef. This study is one of the first to provide demographic and population structure data on the same populations. Demographic data will be used to identify the density and distribution of individuals within age/size classes, and to estimate growth and mortality within age/size classes of the population. Population genetic techniques will be used to examine the relatedness of the different age classes to determine potential larval sources (local or distant).

Results will be used to help predict whether coral populations can maintain cover and population sizes based on growth, mortality and recruitment estimates. Also, predictions will provide insight to the utility of marine protected areas as sources of coral recruits in the Florida Keys National Marine Sanctuary. In addition, the determination of genetic diversity of coral species at Conch Reef will be an important tool for developers and managers of marine resources because protecting the genetic diversity of a species is an important aspect of conservation biology. Populations of Montastrea cavernosa, Porites astreoides, Siderastrea siderea, Stephanocoenia michelini, and Agaricia agaricites will be studied to address the following objectives:

• Characterize the dynamics of the coral populations in terms of recruitment, partial and total mortality, growth rates, and age structure at three depths on Conch Reef.
• Compare the size class distributions of the different species among sites.
• Determine the population genetic structure of each study species at deep and shallow sites.
• Using the genetic data, determine the contribution of local adults to deep and shallow recruits.

These analyses will help to establish if coral populations at each site are in decline, growing or stable, whether Conch Reef is "self-seeding" or dependent on outside sources for population growth, and whether these conclusions differ for different coral species at different depths.