Low high-temperature tolerance of the hydrothermal vent crab Xenograpsus testudinatus: Thermal biochemistry, survival rate and histological analyses, and habitat investigations.

Rising environmental temperatures increase stress on marine organisms, causing physiological damage or death in extreme cases. In this study, we examined the crab species Xenograpsus testudinatus from a shallow hydrothermal vent area in Kueishan Island, off northeast Taiwan. This crab species belongs to the monotypic family Xenograpsidae and is a well-known inhabitant of the shallow hydrothermal vents of Kueishan Island. The maximum temperature tolerance of X. testudinatus and the effects of temperature on this crab species remain unclear. Our laboratory experiments demonstrated the effects of elevated seawater temperatures on the survival and enzymatic function of X. testudinatus. Its mortality rate increased with the elevation of seawater temperature from 25 °C to 40 °C. Survival duration was short (<4 h) when the crabs were reared at 40 °C, and the lethal temperature (LT; death within 7 days of exposure) was 34.74 °C. The response of six enzymes varied with temperature. Significant differences of enzyme activities were noted among various temperature groups (25 °C, 30 °C, 30 °C, and 40 °C) in the gill, but no significant difference was noted in the hepatopancreas. A univariate analysis indicated the temperature level and exposure duration as key factors driving the variations in enzyme activity. A field investigation on the temperature of the seabed where the crabs aggregated revealed that the preferred temperature was <28 °C. Therefore, X. testudinatus does not prefer elevated temperatures. An expected combined effects of temperature tolerance and acidic, sulfuric-rich vent water on X. testudinatus is warrant further investigation.