Growth, maturation and effects of diet in Acanthasterplanci (L.) (Asteroidea) and hybrids reared in the laboratory

Abstract

Specimens of Acanthaster planci (L.) and hybrids ( A. planci × A. brevispinus Fisher) were reared from in vitro fertilization to almost 8 yr of age in a closed-circuit sea-water system. Growth curves of both kinds of starfish were sigmoidal, and logistic growth curves were fitted as first approximations. However, the growth patterns were not strictly logistic because several different phases of growth were evident: (1) a post-metamorphic phase of exponential growth; (2) a phase of Von Bertalanffy-type growth, leading to sexual maturity at 2 yr of age; (3) slow growth after sexual maturity from 2 to 3 yr of age; (4) no growth and shrinkage after 3 yr of age, leading into a senile phase of gonad inactivity and then death at 5 yr of age and later. Phases 1–3 have been recognized in other asteroids. The pattern of growth in A. planci and hybrid starfish is clearly determinate, as has been found for other asteroids in field and laboratory studies. A. planci and hybrids commenced gametogenesis in the latter part of their second year of development; however, gonad development was much greater in the third and subsequent years. There was a seasonal pattern of gonad development and spawning in these laboratory animals, where water temperature was the only apparent cue for this seasonality. At times the starfish were affected by a disease of rapid spreading necrosis, which was controlled by antibiotic treatments. Juvenile A. planci maintained on coralline algae for 2 yr reached a maximum size of 18 mm diameter, about one twentieth the maximum diameter of siblings that made the normal transition to coral feeding. Scallop-fed A. planci reached a maximum diameter ≈ 60 mm smaller than coral-fed A. planci and scallop-fed hybrids. These data support previous observations of the high susceptibility of growth rate and maximum size to diet in asteroids. The influence of an intrinsic factor, appetite, which changes in nature and intensity during the life-cycle, was also evident.