Resumen de Spawning of Three-Year-Old Acropora Millepora Corals Reared from Larvae in Northwestern Philippines
Maria Vanessa B. Baria, Dexter W. dela Cruz, Ronald D. Villanueva, James R. Guest
Polyp age and colony size determine the onset of sexual maturity in scleractinian corals (Hall and Hughes 1996) and this has important evolutionary implications as it influences rates of adaptation and trade-offs between growth and reproduction. Colony age is normally estimated based on size (e.g. Wallace 1985); however, corals have highly variable growth rates and may undergo colony fission, making it difficult to accurately determine age based on size alone. In this study, sexual maturity was examined in a single cohort of three-year old colonies of Acropora millepora that had been reared from larvae. Three out of 12 colonies, transplanted to natural reef after six months of rearing and 17 out of 19 colonies that remained at an in situ nursery were sexually mature. Gravid colonies had geometric mean diameters (GMD) ranging from 12.0 - 27.9 cm, whereas GMD in non-gravid colonies ranged from 7.7 -11.6 cm, indicating that spawning occurs at three years of age provided GMD is > = c. 12.0 cm. Four gravid colonies from the in situ nursery were brought to a land based hatchery for and all colonies spawned synchronously on the night of the full moon (20 March 2011) between 20:30 and 21:30 h. This is the first account of Acropora spawning at three years of age and is 1 year sooner than the previous observation for A. tenuis colonies reared from eggs (Iwao et al. 2010). Here, we accurately determine age and size at onset of sexual maturity in A. millepora demonstrating the potential for relatively short generation times in Acropora corals under ideal conditions. Our findings also highlight the difficulties in estimating age from size alone as the largest colony was more than 3.5 times the diameter of the smallest colony despite being exactly the same age.
