| Monthly collections of the brittle star Ophiopholis aculeata were made and individuals were analyzed using traditional methods (gonad indices, gametogenic stages and oocyte diameters), along with a newly developed quantitative method coined the 'maturity stage index' (MSI). The MSI was statistically related to conventional methods of studying reproduction, but provided greater sensitivity for fine-scale and inter-individual comparisons. This allowed the study of reproductive synchrony in O. aculeata over several scales: (1) within a given habitat, (2) between adjoining habitats, (3) among individuals in each habitat, and (4) within and among natural clusters of individuals. Complementary laboratory trials were conducted to further examine the influence of temperature and spatial distribution on gametogenesis. Ophiopholis aculeata exhibited an annual gametogenic cycle with spawning in late summer. Significant differences were seen between habitats and among individuals in certain months, and synchrony was generally greater around the time of spawning and in nearby/grouped individuals. Laboratory experiments indicated that temperature is unlikely to act as a proximate reproductive cue, and phytoplankton is probably the major environmental factor mediating the annual reproduction of O. aculeata. Together, field and laboratory findings further evidenced the synergistic roles of exogenous factors and inter-individual communication in coordinating the reproductive cycle of marine invertebrates. |
