Enteromorpha intestinalis - a refuge for the supralittoral rock-pool harpacticoid copepod Tigriopus Brevicornis

Supralittoral rockpools form an extreme environment due to severe fluctuati ons in salinity, temperature and oxygen concentration. The only seaweed spe cies in supralittoral rockpools around Great Cumbrae, Firth of Clyde was th e green alga Enteromorpha intestinalis. Only two animal species were record ed permanently over a three year period in this environment; the orange har pacticoid copepod, Tigriopus brevicornis, and the chironomid larva, Halocla dius fucicola. The present study demonstrates the role of the hollow thallu s of E. intestinalis in the lifestyles of T. brevicornis (adults and naupli i) and H. fucicola. The thallus provides a moist refuge reducing desiccatio n when the rockpools completely dry out. Several hundred individuals of T. brevicornis have been observed in a single E. intestinalis thallus. This ob servation may explain how the species can successfully recolonize completel y evaporated supralittoral rockpools after several weeks. The study also ra ises questions about the reliability of previous population estimates of Ti griopus spp. in light of this constantly overlooked refuge.