INFESTATION OF THE FALSE KING CRAB PARALOMIS GRANULOSA (DECAPODA: LITHODIDAE) BY PSEUDIONE TUBERCULATA (ISOPODA: BOPYRIDAE) IN THE BEAGLE CHANNEL, ARGENTINA

Abstract

ABSTRACT A total of 16,692 specimens of Paralomis granulosa was collected in the Beagle Channel, Tierra del Fuego, Argentina, between July 1996 and July 1997. This lithodid was parasitized by a bopyrid isopod identified as Pseudione tuberculata. Infested crabs exhibited a conspicuous bulge on their carapaces, which accommodated the parasite housed in the branchial chamber. The prevalence of infestation by P. tuberculata decreased with crab size, from 45.6% at 10―19.9-mm to 0% at 90―99.9-mm carapace length. Bopyrids were found on 251 occasions in the left branchial chamber and only once in the right branchial chamber. Except for two immature female parasites found in the branchial chamber of a small crab, all parasites were mature females, each usually carrying a dwarf male attached to its abdomen. The length of the female isopods and that of their hosts were positively correlated. These two observations suggest that the parasites infest P. granulosa early in the life of the host, and remain on. and grow up with the host throughout its life. The finding of crabs without bopyrids, but with distended branchial chambers, shows that some crabs survive the infestation. While breeding is inhibited in parasitized hosts, the prevalence of the parasite is already low (about 1.2%) at the size of host maturity. Therefore, we suggest that the reproductive potential of the crab population is not seriously affected by the sterilizing effect of the parasite. Finally, the cooccurrence of this bopyrid and a second parasite, the rhizocephalan Briarosaccus callosus, was recorded, but the prevalence of double infestations was low.