Size-independent investment allocation to regeneration and growth of the branching coral Acropora muricata

Abstract

To reveal the optimal resource allocation among regeneration, growth, sexual reproduction, and survivor-ship in a colonial animal, a specimen of the branching coral Acropora muricata (formosa), without oocytes, was separated into fragments of three different sizes (5, 10, and 20 cm long) that were then transplanted onto coral pavement. Regardless of the fragment size, a wound was fully closed within 11 days after fragmentation. The number of newly formed polyps on the new tissue layer did not differ signifi cantly among fragment sizes. No sig-nifi cant difference was observed in the monthly growth rate among the three fragment sizes. These results showed that regeneration and growth were independent of fragment size. During the observation period, one 5 cm fragment died, the 5 cm and 10 cm fragments did not spawn, but the 20 cm fragments did spawn. The investment to survivorship by the 5 cm fragments might have been smaller than that of the 10 cm fragments, because the 5 cm fragments had smaller energy stocks than did the 10 cm fragments. Combined, these results suggest that the energetic investment for regeneration and growth was constant while investment for reproduction was proportional to fragment size. This fi nding agrees with the theoretical optimal dispersal strategy, in which the allocation to growth by mothers is constant. In conclusion, the colonial coral Acropora muricata generally shows size-independent growth and regeneration, and exhibits a tradeoff among regeneration, growth, survivorship, and reproduction.