Small-scale spatial distribution and oogenetic synchrony in brittlestars (Echinodermata: Ophiuroidea)

There is increasing evidence that spatial factors modulate reproductive processes over large (>150 km) and medium (10–100 km) scales in marine taxa, but few studies have explicitly determined the degree of inter-individual synchrony in gamete development at smaller scales within benthic populations. Using a ubiquitous broadcast-spawning species, the brittlestar Ophiopholis aculeata, we assessed variations in gametogenic activity over the annual reproductive cycle at various scales. Quantitative indices of oogenic maturity were compared in females collected: (1) in two substrata at a given site (distant ∼200–300 m), (2) among clusters of individuals living in relatively close proximity (∼10–50 m), and (3) within each cluster of individuals collected under/inside a given substratum (∼2–20 cm). Gametogenic maturity was also examined in females collected from distant sites (∼50–150 km). At the main study site, oogenic cohesion was greater within and among clusters of a given substratum than between substrata, and differences in reproductive output and spawning periods occurred between individuals from the two substrata studied. At the finest scale (within clusters of individuals) oogenic synchrony was maximal just before spawning. Comparing samples from distant geographic locations (>50 km) showed significant asynchrony outside the pre-spawning period. The present study shows that relatively high levels of asynchrony in gamete maturation may exist among conspecifics of a seemingly homogeneous population, except at the closest scale (within clusters) at the culmination of the reproductive cycle (near spawning). This emphasizes the likely interplay of inter-individual exchanges and small-scale distribution on the fine coordination of reproductive events.