Asynchronous coral spawning patterns on equatorial reefs in Kenya

Abstract

This study examined patterns of reef coral reproduction on lagoonal reefs adjacent to Mombasa in Kenya, at a latitude of 4S. A total of 401 colonies comprising 20 Acropora species was marked and repeatedly sampled between 2003 and 2005 to determine patterns of reproduction at the individual and population level. Spawning was inferred from the disappearance of mature oocytes and spermaries from sequential samples. In comparison to other regions, the overall pattern of coral reproduction in Kenya is one of asynchrony; Acropora species release gametes over a 7 mo period (October to April), with some level of 'temporal reproductive isolation' occurring between species in relation to the lunar month and lunar phase when the main spawning occurred. Extended gametogenic cycles were recorded in A. tenuis, A. valida and Acropora sp. 1, and quiescent non-reproductive periods between cycles were either very short or absent. Spawning occurred during both rising and maximum sea surface temperatures, during both neap and spring tides, and across all lunar periods. The findings from Kenyan reefs support the hypothesis of protracted breeding seasons and a breakdown of spawning synchrony nearer the equator. It is hypothesised that the high fecundities recorded in coral species in Kenya compared to other regions may allow individual reef coral populations to stagger their reproduction over 2 to 5 mo without incurring a significant reduction in fertilisation rates.