Survival strategies on a semi-arid island: submersion and desiccation tolerances of fiddler crabs from the Galapagos Archipelago

Abstract

During tidal cycles, fiddler crabs undergo alternating periods of submersion and desiccation. We compare physiological and biochemical adjustments to submersion and desiccation challenge in two gelasminids from the Galapagos archipelago: the indigenous Leptuca helleri, and Minuca galapagensis. We examine population distributions and habitat characteristics; survival and hemolymph osmolality after 6 h submersion at several salinities, and after 6 or 12 h desiccation; and oxidative stress responses in the hepatopancreas and gills, accompanying glutathione enzyme antioxidant activities, and lipid peroxidation. We provide an integrated biomarker response index based on oxidative stress in each tissue, condition and species. Leptuca helleri occupies a restricted intertidal niche while M. galapagensis is supralittoral. Burrow density in M. galapagensis declined with increasing salinity and decreasing substrate moisture; L. helleri burrow density showed no correlation. After 6 h submersion, L. helleri survived only at 21 parts per thousand S while M. galapagensis survived from 0 to 42 parts per thousand S. After 6 h desiccation, hemolymph osmolality decreased markedly in L. helleri but increased in M. galapagensis. Antioxidant enzyme activities and lipid peroxidation in the hepatopancreas and gills showed tissue- and species-specific responses to submersion and desiccation challenge. The integrated biomarker response indexes for L. helleri were highest in control crabs, driven by oxidative stress. In M. galapagensis, submersion was the determining factor in both tissues. Minuca galapagensis is a generalist species while Leptuca helleri occupies a more restricted intertidal habitat. The species' respective physiological limitations and flexibilities provide insights into how fiddler crabs might respond to environmental change on semi-arid islands.