The effect of Sacculina carcini infections on the fouling, burying behaviour and condition of the shore crab, Carcinus maenas

Abstract

Crabs infected by rhizocephalans usually do not moult. Because moulting is the ultimate defence against fouling epibionts, infected as opposed to uninfected crabs can be expected to harbour a diversity of hard-bottom organisms on their cuticula. Here we provide unequivocal evidence that this is the case in the Carcinus maenas–Sacculina carcini association. In a Danish sample of shore crabs, 75% of sacculinized individuals harboured macroscopic epibionts, whereas only 29% of the uninfected crabs were colonized. The mean numbers of fouling barnacles and serpulid tubeworms per individual were 7.7 and 47.3 for uninfected and infected crabs, respectively, corresponding to coverage of the cuticula by 0.7 and 5.4%. Infected crabs were 12% lower in tissue dry weight than uninfected individuals, which may be a factor causing the moult of sacculinized crabs to be postponed. Finally, a laboratory experiment suggested that infected crabs are less likely to bury than uninfected specimens. Because burying is an important fouling defence, such a parasite-induced behavioural change will favour the colonization by epibionts. It is argued that rhizocephalans infecting crabs from soft-bottom communities may indirectly affect the structure of the free-living benthic community by adding hard-bottom species that otherwise would be absent.

Keywords:

• Barnacles
• community structure
• epibionts
• parasitism
• rhizocephalans
• serpulids

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgments

We are grateful to Annette Bruhn, Søren Busch, Henrik Dam, Søren Krag, Kenneth K. Madsen, Amundur Nolsø, Anne-Mette Norup, Lisbeth K. Pedersen, Iben H. Sørensen, Tenna S. Sørensen and Torben Sørensen for obtaining some of the presented data, and referees for improving the manuscript. The work was supported financially by a grant from the Carlsberg Foundation (K. N. Mouritsen).

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark