The effect of predation and competition on the slow population return of Diadema antillarum

Populations of Diadema antillarum have had low densities ever since its mass mortality event in 1983. A slow population density increase has resulted from fertilization complications due to extensive distance between individuals. The relationships between D. antillarum and their competitors and predators as a cause for the lack of population recovery has not been directly studied. The correlation of D. antillarum density with the abundance of predators, competitors, and microalgae, was studied to determine additional possible explanations for the low density of individuals. There were three dives during the day at six sites. The day dives included observational fish counts and transects and quadrates to assess percent algae cover in a 10 m2 . While the night dives include observation counts of all of the urchins in the 10 m2 . No increase was found in Diadema antillarum density compared with a study in 2009 (0.005 individuals per m 2 ). No significant correlation was determined between D. antillarum density and predator density. A weak, positive correlation between competitor density and D. antillarum density was determined. In contrast, a strong, positive correlation between percent algae cover and D. antillarum density was found This study revealed additional pressures on D. antillarum population (e.g. competitors, percent algae cover), which could account for the slow recovery of local D. antillarum population in Bonaire.

This student research was retrieved from Physis: Journal of Marine Science XIV (Fall 2013)19: 25-32 from CIEE Bonaire.