Populations of amphidromous neritid gastropods are prone to habitat degradation by anthropogenic disturbances. To accumulate information on the life history of these neritids, seasonal growth patterns of four neritid species, Neritina turrita, N. plumbea, N. auriculata, and Clithon brevispina, were examined in an upper mangrove estuary on Ishigaki Island. Individual neritids in a fixed sampling area were captured and mark-released bimonthly over a 1-yr period. Growth rates of the four species were estimated from linear regression models and Ford-Walford graphs using data from recaptured individuals. A model-selection procedure identified the common Lmax model as the best model for describing seasonal growth fluctuations of the four species. Growth of the four species was generally higher in the warm season (April–October) and lower in the cool season (October–April). In addition, N. plumbea stopped growing in midsummer (June–August). Temporal changes in the size-frequency histograms showed several recruitment events of the four species. Estimated growth curves, in some cases, did not fit well to temporal changes of the size cohorts derived from the size-frequency histograms, indicating that size-dependent migration or mortality may occur in the sampling area.
Seasonal Growth Fluctuations of Four Species of Neritid Gastropods in an Upper Mangrove Estuary, Ishigaki Island, Japan
