Population Structure, Spawning, and Growth of the Coral Reef Asteroid Linckia laevigata (Linnaeus)

Abstract

The blue coral reef asteroid Linckia laevigata (Linnaeus) makes up conspicuous adult-only populations on shallow reef flat habitats in the tropical Indo-West-Pacific. Monthly year-round census showed a consistent unimodal size-frequency distribution, with mean arm radius for the population fluctuating from 93.8 to 99.4 mm, at Asan reef flat, Guam, Mariana Islands. This census failed to detect a significant influx of smaller individuals within the population. Searching efforts for this and other asteroids yielded only three pretransformation-stage juveniles and less than 10 transforming young (with arm radius of approximately 50 mm) during a 3-year period (1972 through 1974), in spite of the omnipresence of adults. The L. laevigata population at Asan showed a peak breeding period during the summer months (May to August), as indicated by the spawning activities of sampled adults after they had been injected with 1-methyladenine. Laboratory-grown juveniles attained a mean arm radius of 13.9 mm, 14 months after metamorphosis (15 months after spawning). The juvenile-to-adult transformation is estimated to take place in average L. laevigata at about 2 years of age. Individually marked adults in the field increased 1.1 mm (approximately 1 percent) in arm radius and 0.9 g (approximately 7 percent) in underwater weight (means for 32 individuals) during 5.5 months. The growth rate and population structure indicate that this population of L. laevigata has a low turnover rate with a low level of recruitment.