Population Structure, Growth and Reproductive Biology of the Gorgonocephalid Brittlestar Asteroporpa Annulata

Asteroporpa annulata were sampled in 90 m of water on a rhodolith substrate 48 km southeast of Pensacola Bay, Florida in the Gulf of Mexico. Nineteen collections were conducted by trawl spanning a period from October 1988 to April 1991. Pooled population size frequency analysis revealed a size distribution skewed towards smaller body sizes, Allometric growth over the size range of individuals collected was hyperbolic, with a quadratic function describing the relationship between disc diameter and wet weight, Among a sub-sample of 57 adult individuals, sex ratio was determined to be 2:1 (female:male). Both sexes were of similar body size. Histological examinations of the gonads suggested an annual cycle of reproduction, with a breeding season occurring in the fall and winter. Vitellogenic oocytes measuring 40–50 μm in diameter were present in February. Oocytes had increased to approximately 70–90 μm diameter by April and May, and were in the 100 μm diameter size-class by August. Mature oocytes (130–160 μm diameter) were detected in individuals collected in September 1989 and November of both 1988 and 1989. The energy content of mature ovaries and testes (kJ˙g^–1 dry wt) was 24.6 and 21.4, respectively. Greater levels of energy in the ovaries was attributed to higher levels of lipid (22.6 vs. 9.3% dry wt). It is likely that this species has a broadcasting mode of reproduction, with abbreviated development. No embryos were detected in bursae, thereby ruling out a brooding mode of reproduction. Nonetheless, of the 177 individuals sampled over the course of the study, 2.3% were found to be carrying a single juvenile on the aboral disc. This may be the result of passive settlement or juveniles actively seeking out adult individuals and attaching themselves to the aboral disc.