Reproductive seasonality in an equatorial assemblage of scleractinian corals

• Published in: Coral reefs Vol. 24; no. 1; pp. 112 - 116
• Main Authors: GUEST, J. R, BAIRD, A. H, GOH, B. P. L, CHOU, L. M
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer 01-03-2005; Berlin Springer Nature B.V
• Subjects: Acropora; Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Marine; Scleractinia; Sea water ecosystems; Seasonal variations; Synecology; Asia; Singapore; ISEW, Singapore; Reproductive seasonality; Acropora; Singapore; Spawning; Coral reef; Scleractinia; Marine environment; Synchronous spawning; Coelenterata; Reproduction; Coral; Seasonal variation; Cnidaria; Invertebrata; Community; Equatorial
• ISSN: 0722-4028; 1432-0975
• DOI: 10.1007/s00338-004-0433-7

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). In equatorial regions where sea temperature range and tidal amplitude are often small, it was predicted that reproductive seasonality and synchrony between species would be reduced (Richmond and Hunter 1990). Indeed, the findings of some studies seemed to lend support to this hypothesis. For example, Oliver et al. (1988) reported a reduction in spawning synchrony in three scleractinian species studied at five locations along a latitudinal gradient ranging from the southern GBR (Heron Island, 23 degree S) to the northern coast of Papua New Guinea (PNG) (Madang, 5 degree S). However, more recent studies have found that multi-specific reproductive synchrony does occur in some coral communities, which previously had been thought to be asynchronous. In the Caribbean (Gulf of Mexico), at least seven scleractinian species have been documented spawning synchronously between the seventh and tenth nights following the full moons in August and September (Hagman et al. 1998). In the Solomon Islands (8 degree N), where there is little fluctuation in annual temperature or tidal amplitude, Baird et al. (2001) found that 28 of 41 Acropora species contained mature eggs in the week prior to the full moon in November 1999. In the Karimunjawa Islands (central Java Sea) where sea temperature ranges between 27.5 and 29 degree C, Edinger et al. (in Tomascik et al. 1997) observed 22 scleractinian species spawning over three nights following the full moon in October 1995. Remarkably, virtually nothing is known of the timing of coral reproduction in Southeast Asia, a region that contains more than 30% of the world's reef area and is home to 600 of the almost 800 scleractinian species (Burke et al. 2002). This lack of basic information is particularly worrying as an estimated 88% of Southeast Asia's reefs are threatened by human activities (Burke et al. 2002). Singapore is a small, heavily populated island nation situated at the southern most tip of Peninsula Malaysia, approximately 137 km north of the equator (Fig 1a). In spite of Singapore's proximity to the equator, multi-specific synchronous coral spawning was documented in 2002 occurring after the March full moon (Guest et al. 2002). This study began a week prior to the spawning, on an assemblage of Acropora on the fringing reef at one of Singapore's southern islands. The aim of this study was to determine what time of the year the Acropora spawn in Singapore and to examine the extent of reproductive seasonality and synchrony both among and within species.