Danger on the rise: diurnal tidal state mediates an exchange of food for safety by the bar-bellied sea snake Hydrophis elegans

Prey vulnerability to predation can depend on abiotic conditions. Thus, prey individuals may adjust their investment in anti-predator defense according to changes in one or more abiotic fac- tors. We explored this possibility in Shark Bay, Western Australia, where the bar-bellied sea snake Hydrophis elegans is under threat of predation by the tiger shark Galeocerdo cuvier, asking specifi- cally whether the diurnal tidal state influenced snakes' selection of exposed foraging habitat (sand flat) and refuge habitat (seagrass). At high tide, when both habitats were easily accessible to sharks, H. elegans selected seagrass habitats, where its food is relatively scarce. At low tide, when sharks had limited access to both habitats, H. elegans used the 2 habitats equally but foraged exclusively over sand flats. We concluded that H. elegans is sensitive to the danger of tiger shark predation and trades food for the safety of a refuge when diurnal tidal conditions in its foraging habitat expose it to sharks. Our results suggest that predation risk should be considered in studies of sea snake habitat use and that important variation in predator-prey interactions may be missed if relevant abiotic conditions are ignored.