Comparison of rapid methods for sampling the pipi, Donax deltoides (Bivalvia: Donacidae), on sandy ocean beaches

Abstract

Two rapid methods for sampling Donax deltoides that do not involve sieving sand were compared on a sandy ocean beach in Australia. 'Finger-dredging' of saturated sand in box-quadrats recovered almost 100% of D. deltoides and sampled individuals of all sizes (6 to 55 mm). This method provides the same information as traditional sieving techniques but is faster and should be generally useful for sampling bivalves on sandy beaches. The accuracy of finger-dredging 0.1 m² and 0.2 m² box-quadrats was similar. Sampling was often more efficient with the smaller rather than the larger quadrat, but differences between quadrat sizes varied among levels on the beach. The 0.1 m² quadrat was also preferred because it was fastest and easiest to use and therefore more replicates could be taken per unit sampling time. Tests of a 'knife method' showed that the mean frequency of D. deltoides hit by running the knife through the sand and the mean density of D. deltoides (determined independently) were significantly correlated, but not strongly enough to provide reliable information on abundances. This method adequately sampled only D. deltoides of lengths greater than about 30 mm and was less sensitive in gravelly or saturated sand than in clean, dry sand. The knife method may, however, be useful for studies of the distribution of size classes of large pipis.