Mortality of the gastropod Lepsiella vinosa on the West Head rocky shore in Victoria

This study investigated mortality of egg capsules, juveniles, and adult Lepsiella vinosa on the rocky shore at West Head, Victoria. Observations conducted between 1974 and 1979 indicated that polychaetes, nematodes, nemerteans, planarians and mollusks all prey on L.vinosa egg capsules. It was estimated that at least 43% of embryos found over the study period did not hatch. To estimate juvenile mortality, an area of about 0.5 m2 of shingle beach immediately above the rocky shore was excavated to a depth of 15 cm on 21 July 1978. The shingle was sieved through a series of sieves with the smallest size being 1.00 mm. There were 220 empty L.vinosa shells found in the sample and the majority was between 9.5 and 14.0 mm long. A size-frequency distribution of L.vinosa shells was used to estimate the age of death for each individual. The causes of juvenile and adult morality were probably predation by crabs (e.g. Carcinus maenus) and adverse environmental conditions associated with tide emersion periods and desiccation. The results indicated that juvenile mortality is generally low in the first 3 years after hatching and steadily increases throughout the remainder of the life span (up to 10 years). There was no L.vinosa found in the gut contents of the parrotfishes P.fucicola or P.tetricus. Observations of the study area during high tide periods suggested that no other species of fish or bird prey on L.vinosa at West Head.