Abstract

The reproductive cycles of the bivalves Ensis macha (Molina, 1782), Tagelus dombeii (Lamarck, 1818), and Mulinia edulis (King, 1831) were studied at six sites in southern Chile (38-43°S) from November 1996 to December 1997. Samples of E. macha came from three subtidal shallow depths; those of T. dombeii from two subtidal depths and one intertidal site; and samples of M. edulis originated in one subtidal shallow depth and one intertidal site. Thirty specimens were collected monthly for standard histological analyses. Water samples were also collected to determine salinity, temperature, and chlorophyll a content. In general, the reproductive cycles of the three species were characterized by long spawning periods, beginning during late spring-summer. In some cases, that period extended during autumn-winter until the following spring. The gonads of most of the populations showed quite short recovery periods, with the exception of populations located farther south, which needed more time to begin a new cycle. Comparison of subtidal versus intertidal populations showed that the gonad stages developed more slowly for the latter populations. The earlier results show that variability exists in the timing of gametogenic cycles of E. macha, T. dombeii, and M. edulis along the coast of southern Chile. No significant relationship was found between seasonal variability of reproductive stages and seasonal variability of water characteristics. Among these characteristics, water temperature and chlorophyll a content were the most important. Potential fecundity varied geographically in E. macha and T. dombeii, whereas, in general, no variability was observed in mean sizes of oocytes of the three species. These results must be taken into account when management plans are designed; thus, the timing of the gametogenic cycles of bivalves of economic importance must be studied along their full geographic ranges.