Salinity and temperature tolerance of the mud-flat crab, Helice tientsinensis

Helice tientsinensis burrow in the intertidal mudflats and estuaries especially in the high intertidal and supralittoral zones along the coast of northern China. The mature specimens were collected from Rongcheng, Weihai, China. The salinity and temperature tolerance of the mud-flat crab, Helice tientsinensis, were investigated in the laboratory. The salinity tolerance experiment was conducted at 10℃, 20℃ and 30℃. Ten salinity gradients including 65, 68, 71, 74, 77, 80, 83, 86, 89 and 92 at 10℃, and 56, 59, 62, 65, 68, 71, 74, 77, 80 and 83 at 20℃, and 50, 53, 56, 59, 62, 65, 68, 71, 74 and 77 at 30℃ were respectively designed according to the results of pretests. The temperature tolerance experiment was conducted at salinities of 0, 30 and 50. In the low temperature tolerance test, 6℃, 7℃, 8℃ and 9℃ at 0 salinity, and 0℃, 1℃, 2℃ and 3℃ at 30 salinity, and 3℃, 4℃, 5℃ and 6℃ at 50 salinity respectively designed according to the results of pretests. In the high temperature tolerance test, 34℃, 35℃, 36℃, 37℃ and 38℃ at 0 salinity, and 36℃, 37℃, 38℃, 39℃ and 40℃ at 30 salinity, and 35℃, 36℃, 37℃, 38℃ and 39℃ at 50 salinity respectively designed according to the results of pretests. All treatments were triplicated with ten crabs (16±2)g assigned for each replicate. The results demonstrated that Helice tientsinensis is very tolerant of extreme salinities, and is more tolerant of salinity than several other euryhaline crab species. The mud-flat crabs could survive 96 h in 0 solution at a temperature range of 9～34℃. In hyper-media, values of 96 h LS₅₀, 96 h survival rates of 100% and mortalities of 100% were 72.3, 63.2 and 57.8, and 65, 56 and 50,and 83,74 and 68 at 10℃, 20℃ and 30℃, respectively. Helice tientsinensis tolerate a broad range of temperature condition. The minimum and maximum temperatures that the crabs survived 96 h were 9℃, 2℃and 6℃, and 34℃, 36℃ and 35℃ in solutions of 0, 30 and 50, respectively. In thermal tolerance experiments, the crabs survived 24 h in solutions of 50, 30 and 0 at 38℃, 39℃ and 35℃, respectively, but a sharp rise in mortality of the crabs occurred after 48h of the tolerance experiments. The results showed that the interaction of salinity and temperature significantly affected the survival of Helice tientsinensis(P<0.05). Elevated temperature (range 10-30) decreased the crab's solute tolerance, and sharp changes of the salinity (range 30-50 or 30-0) decreased the crab's temperature tolerance.