Onset of sexual maturity of sexually propagated and wild Favites abdita colonies in northwestern Philippines

Abstract

Scleractinian corals are modular colonial organisms and are the main framework builders of coral reefs. Most corals reproduce by broadcast spawning with external fertilization and these processes are essential to replenish reef coral populations. Despite decades of research, many aspects of coral reproductive biology remain poorly studied. For example, two important reproductive life history traits, colony size and age at the onset of sexual maturity, are mostly unknown for many reef-building corals. In this study, wild colonies of different size classes and colonies of a known age (i.e. colonies sexually cultured and reared from larvae to adults) of the massive scleractinian Favites abdita were examined for the presence or absence of mature oocytes to determine size and age at the onset of sexual reproduction. Fecundity at the onset of reproductive maturity across size classes of wild colonies was also determined. Surveyed and sampled colonies were grouped into three size classes based on maximum colony diameter (A = 0.1-4.0 cm, B = 4.1-8.0 cm, and C = >8.1 cm). For both wild and sexually propagated colonies, the smallest colonies containing gametes were 1.8 cm in diameter, suggesting that this is the minimum colony size at onset of sexual maturity. Colonies of size class A had lower mean oocyte counts per polyp (44 {+/-} 6.08; mean {+/-} SE) compared to colonies of classes B and C (469 {+/-} 62.41, 278 {+/-} 57.15, respectively). However, mean oocyte geometric mean diameter of size class A colonies was greater (340.38 {+/-} 7.68 m) than classes B and C (283.96 {+/-} 6.94 m, 317.57 {+/-} 9.18 m, respectively). Results of this study bring in to question the widely applied operational definition of coral juveniles being colonies [≤]4.0 cm diameter and suggest that even quite small colonies may play a role in contributing to the natural larval pool on reefs than previously thought.