Spatial and temporal variation in fecundity among populations of Acropora millepora on the Great Barrier Reef

Sexual reproduction is vital for population persistence, even in organisms that can reproduce asexually, such as corals. Yet, information on spatial and temporal variation in reproductive traits is surprisingly rare. Here, we examined spatial and temporal variation in fecundity, defined as the number of oocytes per polyp, in the staghorn coral Acropora millepora over 2 yr among 6 populations separated by over 700 km on inshore reefs on the Great Barrier Reef. Variation in fecundity was greatest at small spatial scales: there were pronounced differences in fecundity within and among colonies at each site but little variation at the site or regional scale. This suggests that fecundity is affected by environmental variables that also vary at small scales, such as light and water flow, rather than variables that vary on a regional scale, such as temperature. Colony fecundity in the first year was a good predictor of colony fecundity in the second year, suggesting that some genotypes are more fecund than others. This research suggests that factors operating at the scale of the individual, such as microhabitat differences in flow or light, or genetic identity, are the main cause of variation in fecundity among coral colonies.