Latitudinal variation in the reproduction of Acropora in the Coral Sea

Most comparisons available suggest that synchronous spawning of numerous species of scleractinian corals is restricted to regions with large variations in environmental cycles, such as temperature and tides, with a progressive breakdown in seasonality and synchrony of reproduction towards the equator. Here we compared the reproductive condition of Acropora at 4 locations in the Coral Sea with contrasting environmental cycles. In the Solomon Islands (SI) where environmental conditions varied little, mature oocytes were found in 28 of the 38 Acropora species sampled. This was similar to the pattern on the Great Barrier Reef (GBR) and indicates that synchronous spawning is a feature of coral assemblages in the absence of major environmental fluctuations. In 8 widespread and abundant species the proportion of the population with mature oocytes was 2-4 times lower in the Sl, and a higher proportion of colonies had immature oocytes. These data are consistent with an extended reproductive season in the SI when compared to the GBR. Some asynchrony of gamete release was evident in most species at all locations. In addition, a high number of colonies with no visible gametes suggests that colonies of species which typically participate in mass spawning episodes on the GBR, may miss one or more years ,or spawn at other times of the year.