The hydrothermal vent crab Xenograpsus testudinatus (Crustacea: Brachyura) is endemic near Kueishan Island, Taiwan, where it lives in shallow waters close to the hydrothermal vents located in this area. X. testudinatus is adapted to a sulfur-rich and thus potentially toxic environment. It has established a specialized feeding strategy focusing on dead zooplankton organisms killed by the toxic discharges from the vents. During slack water, when there is little or no current, the crabs leave their crevices to feed on this 'marine snow'. In the present study, we investigated the physiological aspects of nutritional adaptations of X. testudinatus. The crabs showed high digestive capacities of major digestive enzymes and particularly high activities for proteolytic enzymes. This feature can be regarded as an adaptation to irregular food availability. Furthermore, enzymes were stable at elevated temperatures, in a wide pH range, and in the presence of inorganic inhibitors like Cu 2+, Fe 2+, or Co 2+. These enzyme properties can be considered essential to functioning in a vent habitat over long exposure times. Moreover, X. testudinatus is able to store significant amounts of lipid (50 to 60% of dry mass in the midgut gland), which may help to overcome periods of food scarcity. Fatty acid profiles revealed high amounts of saturated and monounsaturated components (mainly 16:0, 16:1(n-7), 18:1(n-9), and 18:1(n-7)). These findings reflect physiological adaptations and energetic strategies that enable this crab to exist in this extreme hydrothermal vent habitat. © Inter-Research 2012.