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

Abstract

The dispersion patterns and reproductive strategies of 2 fungiid coral species (Fungia granulosa and Fungia scutaria) from the northern Red Sea are examined. P. scutaria is found in aggregations on shallow water patch reefs at 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 and 25 m. Both species are gonochoric broadcasters, releasing gameres in the summer months, with gonad development beginning in early spring. The different reproductive strategies of the 2 species are expressed by the differences in size at maturity and length of reproductive period. Reproductive indices suggest a relatively long reproductive season for F. scutaria (June to September) and a shorter one for P. granulose (July to August). F. scutaria spawns on the evening or evenings immediately following the full moon, whereas F. granulosa shows no correlation to lunar phase and spawns during daytime. 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 males, while very large individuals (> 9.0 cm in length) were all females. This indicates either protandry or that males reach sexual maturity at a smaller 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 in F. granulosa 1.1:1. Budding was more prevalent in the shallow-water-dwelling F. scutaria than in the deeper-water-dwelling F. granulosa. The differences in distribution pattern, reproductive timing, prevalence of budding and sex ratio found between the 2 species of fungiids indicate that the primary form of recruitment of the shallow water F. scutaria may be through asexual reproduction. These results suggest that the evolution of different reproductive strategies in closely related species may be in part the consequence of different environmental constraints.