Meeting Abstract
24.5 Jan. 5 The chemically-mediated orientation and feeding behaviors by the hydrothermal vent crabs Xenograpsus testudinatus�What makes them swarm in such high densities? HUANG, H.-D.*; JENG, M.-S.; Academia Sinica; Academia Sinica symbiose@gate.sinica.edu.tw
The crab Xenograpsus testudinatus lives at enormously high densities around the sulfur-rich hydrothermal vents found in shallow waters off Kueishan Island, northeastern Taiwan. During slack water, thousands of Xenograpsus crabs swarm out of the sulphur-rich crevices, and begin to feed on the sea floor near the vents spewing sulphurous plumes and bubbles. These crabs scavenge food particles and dead animals, mainly the zooplanktons killed by toxic vent plumes (Jeng et al. 2004). We hypothesize that X. testudinatus use chemical cues to aggregate and forage together. In laboratory, we tested crab responses to chemical cues from congeners, sulfur sands, Na2S solution, and smashed shrimp meat. Crabs oriented toward odors of congeners and shrimp meat, but avoided sulfurous seawater. With presence of the food scent, Xenograpsus crabs stood high on their legs, and explored through substrate with their appendages. The frequencies of the foraging behavior, bringing pinches of surface sediment to the buccal region with their chelae, and processing with the mouth appendages, were also increased. We conclude that, instead of locating the sulfur from the vents, X. testudinatus use chemical cues from congeners to stay together and close to food sources. In their nutrient-poor environment, this foraging behavior enables these opportunistic feeders to maximize their efficiency in harvesting the plankton kill coinciding with tide currents.
