Effect of predator-prey and competitive interactions on size at emergence in the black-lip abalone Haliotis rubra in a Tasmanian MPA

Following more than a decade of protection from fishing activity, the direct and indirect effects of fishing on benthic community structure are becoming apparent inside no-take marine protected areas (MPAs) on Tasmania’s east coast. Gradual increases in the abundance and average size of putative abalone predators inside the no-take Maria Island Marine Reserve (MIMR) have coincided with increases in the minimum size of the emergent abalone Haliotis rubra. This suggests that the threat of predation may influence the structuring of abalone populations. The abundance of emergent abalone was negatively associated with predator abundance, especially the rock lobster Jasus edwardsii, inside the MPA and in adjacent fished areas. Abalone leave cryptic habitat at smaller sizes in fished areas compared to abalone inside the MPA. Although the patterns in abalone size at emergence (SAE) were strongly correlated with rock lobster abundance and average size, the abundance of other predators (demersal predatory fish and crabs) or competitors (sea urchins) did not influence the patterns in abalone SAE. However, predation mortality in isolation could not account for the differences we observed in abalone size frequency distributions between MPA and adjacent fished locations. We suggest that a combination of factors including predation, intra and interspecific competitive interactions are responsible for patterns in abalone SAE.