Genetic discrimination of sacculinid parasites (Cirripedia, Rhizocephala):Implication for control of introduced green crabs (Carcinus maenas)

We used nucleotide sequence data from the ribosomal RNA (rRNA) gene cluster to determine the affinities of rhizocephalans reported to be Sacculina car cini which parasitize different portunid hosts: the green crab Carcinus mae nas from Sweden; C. maenas from England; Liocarcinus marmoreus from Ireland ; and Liocarcinus holsatus from Wales. There were no differences in nucleot ide sequence data from the 3' region of the small subunit (SSU) (160 bp) an d internal transcribed spacer 1 (ITS 1) (274 bp) rRNA of these parasites. T he same region was sequenced from Sacculina granifera from Queensland, Aust ralia, parasitic on Portunus pelagicus; Sacculina oblonga from Kyushu, Japa n. parasitic on Cyclograpsus intermedius; and an undescribed rhizocephalan from Victoria, Australia, parasitic on Nectocarcinus integrifrons. The cons ensus nucleotide sequence of S. carcini from the ITS 1 rRNA differed from S . granifera by 52% (146/282 sites), from S. oblonga by 56% (162/289 sites) and from the rhizocephalan from N. integrifrons by 33% (94/284 sites). The consensus nucleotide sequence of the 3' region SSU rRNA of S. carcini and t he rhizocephalan from N. integrifrons, which included the V9 domain, differ ed from S. granifera and from S. oblonga by 6% (9/160 bp) The high divergen ce rate of ITS 1 rRNA sequence between species of Sacculina makes it a valu able diagnostic tool for parasites in this genus. On that basis, the nucleo tide sequence data suggest that S. carcini infests at least two genera of c rabs from a broad geographic distribution. This may limit the use of this p arasite for biological control of introduced populations of green crabs.