Occurrence of a New Zealand pea crab, Pinnotheres novaezelandiae, in five species of surf clam

Abstract

In samples from 60 random stations in four depth strata along the Manawatu-Horowhenua coast north-west of Wellington, Pinnotheres novaezelandiae was found in Mactra discors, M. murchisoni and Spisula aequilateralis but not in Paphies donacina or Dosinia anus. This is the first record of P. novaezelandiae from M. murchisoni. The incidence of P. novaezelandiae in each of the three infested species of surf clam was compared. Significantly more pea crabs were found to infest M. discors than M. murchisoni or S. aequilateralis. In Mactra discors the occurrence of pea crabs decreased with increased depth. Carapace widths of pea crabs from M. discors were significantly larger than those from M. murchisoni and S. aequilateralis. No significant differences were found between the carapace widths of pea crabs from M. murchisoni and S. aequilateralis. Crab size was positively correlated to host shell length, with significantly larger crabs inhabiting significantly larger shellfish. Pinnotheres atrinacola was recorded for the first time from S. aequilateralis.