Research Abstract

To determine if the theories which govern island biogeography hold at the population level, I tested the relationship between two species native to The Great Barrier Reef. On intertidal reef flats, the giant clam Tridacna crocea bores into the desiccated portions of the hard coral, Porites lobata. I defined patches of P. lobata as islands and posed two questions. First, do abundance, shell length or biomass of T. crocea correlate with P. lobata patch surface area? Second, do T. crocea individuals require a minimum P. lobata patch surface area for successful settlement? I surveyed 50 patches of P. lobata inhabited only by T. crocea for surface area, T. crocea abundance, and individual shell length. I also estimated T. crocea biomass. Surface area was calculated for 30 P. lobata patches with no inhabiting T. crocea individuals. A T-test indicated a significant difference in patch size between colonized and non-colonized P. lobata. Regression analysis revealed a positive correlation between P. lobata surface area and T. crocea abundance. Results also revealed positive correlations between P. lobata surface area and T. crocea biomass, as well as between P. lobata surface area and T. crocea total shell length. There was not a significant correlation between P. lobata patch surface area and T. crocea mean shell length. Multiple regression analysis revealed that as P. lobata surface area increased, both T. crocea mean shell length and T. crocea abundance increased. These results may indicate that colonization rates increase with patch area, while the size of existing individuals remains relatively constant through time.