Reproductive periodicity of the tropical intertidal chiton Acanthopleura gemmata at One Tree Island, Great Barrier Reef, near its southern latitudinal limit

Abstract

Reproduction in the pantropical chiton Acanthopleura gemmata was examined at One Tree Island, Great Barrier Reef, near the southern limit of its distribution, using gonad histology and gonad index (GI). Gonad growth was associated with the onset of gametogenesis in mid-spring. Fully mature gonads were present from early summer until late autumn. During these months gametes at various stages of development were present in the gonads indicating a continuous pattern of gamete development and release over the six month spawning season. Following the maximum GI (March/April) there was a sharp drop in the index marking the end of spawning. In winter, the gonads entered a rest period and remained small in size. The reproductive pattern of A. gemmata at its southern limit is similar and 6 months out of phase to that reported for populations in the Gulf of Suez, at the northern limit of its distribution. This suggests that photoperiod may be an important factor in modulating reproduction. Reproduction of A. gemmata at One Tree Island is also similar to that for populations in the northern Great Barrier Reef.