Seasonal patterns of coral reproduction on equatorial reefs in Mombasa, Kenya Sangeeta MANGUBHAI 1 and Peter L. HARRISON School of Environmental Science and Management, Southern Cross University, P.O. Box 157, Lismore, New South Wales 2480, Australia 1 Present address: P.O. Box 10135, Bamburi, Mombasa 80101, Kenya FAX: 254-41-5486 473, e-mail: smangubhai@africaonline.co.ke Abstract Only a few studies have examined sexual reproductive patterns of scleractinian corals in equatorial regions. It has been suggested that spawning synchrony breaks down on equatorial reefs due to weak environmental cues governing the onset and timing of reproduction. This paper presents the first data on the seasonality and timing of reef coral reproduction events in lagoonal reefs adjacent to Mombasa in Kenya, at latitude 4ºS. Samples were collected from tagged colonies every 2-8 weeks from April 2003-May 2004, and reproduction was inferred from the disappearance of mature-colored oocytes and spermaries from sequential samples. Three faviids (Echinopora gemmacea, Platygyra daedalea, P. sinensis) and 17 Acropora species were found to be hermaphroditic, and are likely to be broadcast spawners. Echinopora gemmacea and the majority of Acropora species had a single annual gametogenic cycle, while some colonies of P. daedalea and P. sinensis reproduced bi-annually. Less than 20% of Platygyra species participated in a minor reproductive event in August-October which coincided with the southeast monsoon, while >97% reproduced in late February-early March during the northeast monsoon. Acropora species reproduced over a 7-month period with the majority reproducing during the northeast monsoon between January-March when seawater temperatures were close to their summer maximum, averaging 28.3ºC. Within the reproductive season individual Acropora species had peak periods when ~50% of the population reproduced. These peak periods occurred at different periods for the different species suggesting some degree of ‘temporal reproductive isolation’ similar to that observed in the Red Sea. However, some Acropora species had an extended reproductive season spanning 2- 5 months. Keywords: reef coral, reproduction, equatorial reefs, Kenya Introduction Research over the last two decades has shown broadcast spawning of gametes for external fertilization to be the dominant mode of reproduction in scleractinian corals (see reviews by Harrison and Wallace 1990; Richmond and Hunter 1990). Spawning patterns have been described for coral communities in a number of different regions including the Western and Northern Pacific (Great Barrier Reef, Harrison et al. 1984; Willis et al. 1985; Babcock et al. 1986; Japan, Heyward et al. 1987; Hayashibara et al. 1993), Central and Eastern Pacific (French Polynesia, Carroll et al. 2004; Costa Rica, Panama, Galapagos Islands, Glynn et al. 1991, 1994, 2000), Red Sea (Shlesinger and Loya 1985; Shlesinger et al. 1998) and Caribbean (Szmant 1986; Richmond and Hunter 1990; van Veghel 1993). Only one paper has been published on the reproductive patterns of corals in the Western Indian Ocean, which found 5 soft coral species to be gonochoric broadcast spawners, 1 soft coral to be a gonochoric brooder and 1 hard coral to be a hermaphroditic broadcast spawner, in South Africa (Schleyer et al. 1997). All species demonstrated synchronized spawning, with Pocillopora damicornis releasing mature gametes over 1 or more nights at, or after, the new moon in January (summer).