THE IMPORTANCE OF CREVICES TO THE INTERTIDAL SNAIL LITTORARIA-ARTICULATA (PHILIPPI) IN A TROPICAL MANGROVE FOREST

The intertidal gastropod, Littoraria articulata (Philippi), is common on the trunks of mangroves at Coorooman Creek, Central Queensland. Ind ividuals of shell length less than 3 mm were only found in empty tests of the barnacle Hexaminius popeiana (Foster). Larger snails were expo sed on the trunk or occasionally in crevices such as knot holes. The r elationship between shell length and shell strength differed between b arnacle dwelling and larger L. articulata. in both cases it was linear , but the rate of increase of strength with increasing length was sign ificantly greater for barnacle dwelling snails than for exposed ones. In contrast, there was an exponential relationship between shell stren gth and length for the weaker shelled Littoraria filosa (Sowerby), whi ch occurs higher on the tree and does not inhabit barnacles. The survi val of L. articulata was affected by the presence of crevices signific antly fewer disappeared from posts with artificial crevices than from those which lacked them, and some snails tethered to posts appeared to have been eaten by fish. The importance of crevices is discussed in r elation to predation pressure, growth and habitat selection by larval L. articulata.