Comparison of juvenile coral assemblages between Australia's Coral Sea and Great Barrier Reef Marine Parks

Densities of juvenile corals (<= 50 mm diameter) are expected to vary between geographically isolated and more spatially proximate reefs, and may constrain local recovery potential. This study compared juvenile coral densities and their relationships with local abundance of adult congenerics at geographically isolated reefs within Australia's Coral Sea Marine Park (CSMP) versus highly connected reefs within the Great Barrier Reef Marine Park (GBRMP). Three latitudinal regions and two habitats (reef crest and slope) were examined within both marine parks to test for spatial variation. Densities of juvenile corals in the CSMP (13.99 +/- 0.72 juveniles 10 m-2) were significantly lower compared to those in the GBRMP (23.72 +/- 1.86 juveniles 10 m-2). Specifically, there were significantly less Acropora and Pocillopora juveniles on the reef crest in the central CSMP compared to the GBRMP. Relationships between juvenile abundance and percent coral cover were greatest for Acropora and Pocillopora in the GBRMP. This may be due to the low range of coral cover estimates recorded in the CSMP, especially for Acropora (0-15%). Low juvenile coral abundance, and in particular, the lack of fast-growing juvenile corals (e.g., Acropora) in the Central CSMP, in combination with low cover of broodstock (particularly Acropora) on CSMP reefs, poses a significant constraint on post-disturbance recovery capacity, possibly attributable to isolation and limited connectivity among reefs in this region.