Biannual coral spawning decreases at higher latitudes on Western Australian reefs

Seasonal differences in the timing of multi-specific coral spawning between the east and west coasts of Australia may be the result of a genetic legacy or of adaptation to local conditions. Using estimates of the proportions of coral species that spawned in spring and autumn at Ashmore Reef (12A degrees S) and Ningaloo Reef (23A degrees S) in Western Australia, in combination with findings of previous surveys, I examined whether reproductive seasonality varied with latitude. A consistently high proportion of species spawned during the main reproductive season in autumn regardless of latitude. However, there was a clear decrease in the proportion of species spawning in spring, from an average of 49 % at Ashmore Reef (12A degrees S) to 7 % at Ningaloo Reef (23A degrees S). The results of this study suggest that seasonality of coral reproduction in Western Australia reflects environmental gradients and natural selection rather than an inherited genetic legacy.