Effect of Colony Size, Polyp Size, and Budding Mode on Egg Production in a Colonial Coral.

Abstract

The factors that influence egg production in the massive coral Goniastrea aspera were examined in colonies of various sizes collected before the first spawning of the year. Particular attention was given to polyp size, measured in three dimensions as volume. Although a polyp in a colony containing as few as 13 polyps produced eggs, colonies with fewer than 60 polyps had fewer eggs per unit volume of polyp. The relationship between colony size and colony fecundity suggested that 60 polyps is the minimum size at which a colony can achieve active maturity. Polyp volume of small colonies before maturation was also smaller than that of the larger colonies, suggesting that colony size, as well as polyp size, is crucial for sexual maturity. The position of a polyp in the colony (and thus its mode of budding) also affects its maturity (and thus its egg production). Marginal polyps (those on the edge of the colony) usually exhibited extratentacular budding, and the resulting polyps were initially immature. Consequently, egg production by such polyps is a function of their age, calculated from the time of their formation by extratentacular budding. In contrast, non-marginal polyps always exhibited intratentacular budding. Moreover, in the non-marginal areas of large colonies (>84 polyps), the polyps produced by intratentacular budding were always mature. In all colonies, marginal polyps were smaller in volume and had a lower number of eggs for each unit of volume than did non-marginal ones. This suggests that polyps play different roles according to their position in a colony: marginal polyps contribute to defense and expansion of the area of attachment, whereas the role of non-marginal polyps is reproductive. The fecundity of mature colonies increased linearly with colony size, and large colony size cannot be attained without expansion of the attachment area.