Reproductive seasonality in an equatorial assemblage of scleractinian corals

Abstract

[Extract] Multi-specific, synchronous spawning of scleractinian corals was first documented on Australia’s Great Barrier Reef (GBR) in the early 1980s (Harrison et al. 1984). There, over a period of eight nights in late spring, at least 133 coral species released their gametes for external fertilisation and more than 30 species spawned on the same night on one reef (Willis et al. 1985; Babcock et al. 1986). However, the causal factors responsible for this remarkable phenomenon are still not clearly understood (see review in Harrison and Wallace 1990). Comparisons of reproductive patterns—from sites at a variety of latitudes, with contrasting seasonal and environmental conditions—can help to elucidate the ‘‘ultimate’’ causes of reproductive seasonality and synchrony (Oliver et al. 1988). Early examples of such comparisons showed that multi-species reproductive synchrony is not a characteristic of all coral communities (Richmond and Hunter 1990). In particular, studies in parts of the Red Sea and the Caribbean found that corals at those sites tended to spawn asynchronously (Shlesinger and Loya 1984; Szmant 1986). This lack of synchrony was attributed to a reduction in environmental seasonality and a narrowing in the ranges of certain environmental parameters, in particular annual sea surface temperatures (Richmond and Hunter 1990) and tidal amplitudes (the difference between mean low water springs and mean high water springs) (Oliver et al. 1988).