Reproductive strategies of two fungiid corals from the northern Red Sea: environmental constraints?

The dispersion patterns and reproductive strategies of 2 fungiid coral spec ies (Fungia granulosa and Fungia scutaria) from the northern Red Sea are ex amined. F. scutaria is found in aggregations on shallow water patch reefs a t depths of up to 5 m. F. granulosa is more randomly distributed, on sandy substrates and rocky slopes, and is most abundant at depths of between 15 a nd 25 m. Both species are gonochoric broadcasters, releasing gametes in the summer months, with gonad development beginning in early spring. The diffe rent reproductive strategies of the 2 species are expressed by the differen ces in size at maturity and length of reproductive period. Reproductive ind ices suggest a relatively long reproductive season for F. scutaria (June to September) and a shorter one for F. granulosa (July to August). F, scutari a spawns on the evening or evenings immediately following the full moon, wh ereas F. granulosa shows no correlation to lunar phase and spawns during da ytime. In addition, a sexual dimorphism according to size was found for F, scutaria: small individuals (2.5 to 6.0 cm in length) were predominantly ma les, while very large individuals (>9.0 cm in length) were all females. Thi s indicates either protandry or that males reach sexual maturity at a small er size than females. F. granulosa begins reproducing at a length of 5.5 cm (the diameter along the mouth axis) and no size related sexual dimorphism was found. The sex ratio of males to females in F. scutaria was 1.9:1 and i n F, granulosa 1.1:1. Budding was more prevalent in the shallow-water-dwell ing F, scutaria than in the deeper-water-dwelling F, granulosa. The differe nces in distribution pattern, reproductive timing, prevalence of budding an d sex ratio found between the 2 species of fungiids indicate that the prima ry form of recruitment of the shallow water F. scutaria may be through asex ual reproduction. These results suggest that the evolution of different rep roductive strategies in closely related species may be in part the conseque nce of different environmental constraints.