THE PARASITIC RHIZOCEPHALAN BARNACLE SACCULINA CARCINI IN CRABS OF THE FORTH ESTUARY, SCOTLAND

摘要

In the Forth Estuary, Scotland, parasitic rhizocephalan barnacle Sacculina carcini extemae or scars occurred on 6.4/100 of Carcinus maenas from the subtidal channel of the middle estuary. These became more frequent downstream, infecting 46.9/100 in the lower estuary basin. Male and female crabs were infected equally, and infection rates in low- tide samples did not differ from high-tide. The parasites occurred most frequently on crabs of 40-50 mm carapace width (CW) rather than the modal crab size class of 50- 60mm. Downstream, proportionately more smaller than larger crabs bore parasites whereas, further upstream, more larger than smaller crabs bore parasites. There is evidence for the annual appearance of new externae in July-October, especially in the lower estuary basin, followed by their growth and loss after about a year.