Micro-scale genetic heterogeneity and structure in coral recruitment: fine-scale patchiness

Coral reefs have recently suffered severe environmental perturbations.Genetic variability and structure in coral populations is important in determining their survival and adaptation and can be influenced by larval settlement/recruitment.Here, we assess the genetic heterogeneity of Agaricia agaricites coral recruits at 3 spatial scales on the East Flower Garden Bank, Gulf of Mexico.Racks with settlement plates were placed at each of 3 sites, at 23 m depth, arranged in a circular pattern, 10s of meters apart.Three racks were placed within each site, several meters from each other.Each rack held 5 terracotta settling plates, several centimeters apart.Highly polymorphic markers for amplified fragment length polymorphisms (AFLP) were used to assess genetic structure among recruits: among sites, racks, and plates.Four sets of AFLP primers yielded 164 polymorphic markers.The assignment-based statistical programs AFLPOP and STRUCTURE assigned coral spat back to their original sites (home populations) at levels of between 63.3 and 99.8%.Recruit populations exhibited clear, consistent genetic heterogeneity at a scale of 10s of meters.The levels of assignment back to rack home populations were broader, ranging from 32.5 to 96.5%.Highest rates of selfassignment/ identification of distinct/separate populations occurred at the smallest spatial scale, i.e. the plates (5 3.7 to 96.5%).Genetic relatedness among recruits was highest and patchy at a scale of 10s of centimeters, more variable at a scale of meters, and still detectable at a scale of 10s of meters.Genetic variability in these recruits was high.Recruitment was probably local, from corals in the immediate vicinity, and with limited mixing.