3.1. Genetic structure of Acropora palmata populations in the Caribbean
 

Knowledge of Acropora population structure is essential for assessing its degree of threat and deciding on appropriate conservation measures.  If, for example, we find very low genetic diversity (i.e. few genets) within individual stands and/or across the region, it might suggest that its status is under much greater threat than would be judged from its overall abundance.
 

Polymorphic markers were developed and tested. We used gametes in the development process to preclude contamination caused by zooxanthellate symbionts that are present in adult tissues.

The high amount of polymorphism of the markers makes it unlikely that two none-clonemates would share identical genotypes. Thus, clonal identity of samples can be ascertained. Clonal structure varies both within and across regions. Notably, two adjacent reefs in the Key Largo area of Florida (Horseshoe and Little Grecian reefs, 3.3 km distance) showed very little clonal variation. We analyzed 22 colonies on Horseshoe Reef all of which are clonemates (or ramets). That means that all 22 colonies share one genotype and are one genetic individual (called a genet) (Fig 1 a). The same pattern was found at Little Grecian reef where 24 colonies were analyzed (Fig 2 b). Again, all belonged to the same genet. However, this genet was different from the one found at Horseshoe Reef. In other words, even though over 30 colonies of Acropora palmata grow on either reef, they might represent as little as two distinct individuals demonstrating that the effective population size of this coral might be overestimated by just counting the number of colonies present. In contrast, Sand Island reef located close by (<15km distance) showed high clonal variation with 19 out of 47 (=40%) collected colonies being unique genotypes (Fig 1 c). 

The markers developed here have the potential to unravel the genotypic diversity of a major reef building coral species suspected of highly clonal population structures. Preliminary results indicate a wide range of genotypic diversities both locally and across the Caribbean.

Preliminary analysis of population structure in the Caribbean indicates that A. palmata populations show little but significant substructure. Thus, larval exchange may be limited between certain reefs. If this holds true after the number of samples analyzed has increased it would indicate that A. palmata populations would have to be managed on a local scale.
 

Baums, I.B. (2002) Genetic status of Acropora populations in the Caribbean. Presentation as an Invited Speaker at the Caribbean Acropora Workshop: Potential Application of the U.S. Endangered Species Act as a Conservation Strategy, Miami, Florida.