Ecological studies on intertidal dog whelks (Gastropoda: Nassariidae) off Northern Minahasa, Sulawesi, Indonesia
General features of dog whelks (Gastropoda: Nassariidae) communities of tropical tidal flats are defined from Northern Minahasa, Sulawesi Indonesia, based on surveys from August 2000 to July 2001 at Arakan, Mokupa and Likupang. Six species are founded at Arakan, while five and four species are founded at Mokupa and Likupang respectively. A zonation of nassariids communities is described. Total average densities ranged between 8 ind m-Â² in the middle zone of Arakan and < 1 ind m-Â² in the lower zone of Mokupa and Likupang. Nassariids densities differed significantly among study sites as well as among in tidal zones. The population dynamics of Nassarius pullus and N. bimaculosus were investigated by analysis of monthly size-frequency histograms. Shell lengths of N. pullus ranged from 6 to 21 mm-below. Quite large individuals (ï‚³ 16 mm-below) are dominated the samples and formed stationary mode at 18 mm-below. N. bimaculosus, ranging in size from 6 to 19 mm-below, a more dynamic development was visible. The von Bertalanffy growth (VBG) parameters were estimated to describe the individual growth of the two nassariid, were Lï‚¥ = 22.6 mm, K = 0.78 year-1 and t0 = -0.12 year for N. pullus and Lï‚¥ = 20.5 mm, K = 1.00 year-1 and t0 = -0.10 year for N. bimaculosus. Size at maturity (L50) were 15 and 16 mm for N. pullus while N. bimaculosus mature at size of 13 mm. There is evidence that recruitment took place throughout the whole year for both species. Maximum age was about 3.85 years for N. pullus and 3.00 years for N. bimaculosus. The examination of gonad development stages for both species shown that gametogenesis was not synchronized between the individuals and most female gonads contained gametes at different stages of development and there were only very few gonads in a â€˜post-spawningâ€™ condition.