Spawning patterns of scleractinian corals at theSolitary Islands - a high latitude coral communityin eastern Australia

The timing and synchrony of reproduction in scleractinian corals varies greatly among geographic locations, along latitudinal gradients, and among regions. On the east coast of Australia, there are extensive subtropical coral communities within the Solitary Islands Marine Park (30°S). From 1994 to 1996, the pattern of reproduction was studied in 27 species from 10 genera of broadcast spawning scleractinian corals. Spawning periods were determined directly from observations of 4 species that spawned in aquaria, and indirectly from repeated sampling of 236 tagged field colonies by noting the disappearance of mature gametes. Evidence of sexual reproduction was observed in 24 coral species, and gametes were released annually from December to April. Spawning periods were staggered among species and among colonies within some species. Spawning in massive species was generally more synchronous and predictable than for acroporid species. Massive coral species spawned from 8 to 12 nights after a full moon, whereas there was no obvious lunar periodicity of spawning among acroporid corals. This asynchronous pattern of reproduction contrasts with the highly synchronous spawning of more than 140 coral species during mass spawning periods on the Great Barrier Reef (GBR) in October to December each year. The delay in the timing of coral spawning at the Solitary Islands compared with the GBR coincides with the delayed rise in sea temperatures in the subtropics. In addition, the highly variable nature of sea temperatures at the Solitary Islands around the time of gamete maturation and spawning may account for the less synchronous pattern of reproduction in this high-latitude coral community.