THE ECOLOGY OF THE SANDY BEACHES OF THE CAPE PENINSULA, SOUTH AFRICA. PART 4: OBSERVATIONS ON TWO INTERTIDAL ISOPODA, EURYDICE LONGICORNIS (STÜDER) AND EXOSPHAEROMA TRUNCATITELSON BARNARD

Summary

Two isopods, Eurydice longicornis and Exosphaeroma truncatitelson, have been studied in the field and in the laboratory with a view to elucidating aspects of their ecology. Particular attention has been given to factors which may be relevant to their distribution, as the two species are virtually segregated in the field. It is shown that both species favour some grades of sand over others, Exosphaeroma choosing finer substrates than Eurydice. Choice is made by trial burrowing. Studies of burrowing behaviour, depth of burrowing and reactions to water currents also demonstrate that Eurydice is better adapted to life on exposed sandy beaches than is Exosphaeroma. The food relationships of the animals, their reproduction, responses to light and hydrostatic pressure are dealt with briefly. In addition to a comparison between Eurydice and Exosphaeroma on Cape Peninsula beaches, an attempt is made to compare Eurydice longicornis with the European E. pulchra.