Adaptation of Coenobita scaevola (Forskal) Crustacea, Anemura) to terrestrial life desert-bordered shore line

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Achituv* & M. Ziskind
Department of Life Sciences, Bar Ilan University, Ramat Gan 52100, Israel
ABSTRACT: Coenobita scaevola (Forskal) is a terrestrial hermit crab inhabiting shores of the S~nai
Peninsula, where animals encounter severe conditions of high temperature, high radiation and low
relative humidity. Adaptation of these crabs to such arid conditions was studied. The crabs are
nocturnally active, taking refuge during the day in hiding places with milder conditions. Body
temperature follows that of their hiding places, which is lower than that of the air. After ca 6 h exposure
to direct radiation, the crabs die. Thermoregulatory abil~tyis low. Water loss is lower In shelled crabs,
higher in crabs without shell; the shell protects the abdomen from desiccation. Freshly killed crabs
evaporate less than live crabs, suggesting that evaporation from live crabs is not a purely passive
process. Gill surface area is small in comparison with aquatic crabs. Aquatic oxygen consumption is 1.4
times higher than aerial. Unlike other Coenobita spp. which inhabit sites distant from the sea, and in
spite of successful adaptation to terrestrial life, Coenobita scaevola does not penetrate far inland: In
desert conditions it depends on the sea for its only water source.