MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps14668

ABSTRACT: The activity pattern of the shallow water hydrothermal vent crabs Xenograpsus testudinatus in the vent and peripheral regions of Kueishan Island, Taiwan, was observed using an underwater time-lapse camera with infra-red lighting during seven consecutive 2-3 day periods. Hourly tide levels, in-situ water temperature, pH, and light intensity were recorded to examine any effect of these environmental factors on the crabs' activity. Time series analysis using spectral density plots indicated that crab activities were not rhythmic. Nevertheless, cross-correlation analysis and Pearson’s correlation showed that crab density in the vent region was negatively correlated with tides but positively correlated with water temperature and light intensity. Stepwise multiple regression analysis showed water temperature, tide levels and light intensity are significant predictors on crab density. There were no significant differences in crab density among specific tide periods, and thus, previous hypothesis that vent crabs came out in large swarms during slack waters was rejected. The vent region is a refuge from predators, with crabs more active during daytime low tides and during periods when there are higher water temperatures. Crab density in the peripheral region is positively correlated with tides but negatively with pH, indicating that crabs there are more active at high tides for foraging and during periods with lower pH probably when there are fewer predators. Stepwise multiple regression revealed pH and tides were significant predictors for crab density in the peripheral region.