Salinity tolerance of hard stage Pinnotheres bidentatus (Decapoda: Brachyura: Pinnotheridae)

Abstract

Salinity tolerance of hard stage Pinnotheres bidentatus, was studied during November and December of 1996. The pea crabs were collected from tidal waters at Kaomei tidal flat during night-time flood tides during full or new moons using 1-mm mesh plankton nets. Survival of these pea crabs under a wide range of salinity (0 to 30 ‰ salinity with intervals of 5 ‰ salinity and 0 to 5 ‰ salinity with intervals of 1 ‰ salinity) was examined. Only 0 ‰ salinity treatments had 100% mortality rates, whereas no mortality occurred in the rest of salinity treatments. These results indicate that hard stage P. bidentatus may be tolerant to a wide range of salinities, but it cannot survive if suddenly exposed to freshwater. Sudden exposure to 0 ‰ salinity may be seen in some parts of the tidal flat area during seasons of abundant freshwater influx and human fishery activities. However, active swimming behavior of the hard stage pea crabs observed in 0 ‰ salinity treatment suggests that these free-swimming pea crabs may be able to avoid unfavorable salinity conditions by moving out of the area.