Nassariid whelks hitch-hiking on Cancer pagurus: phoresis, commensalism or fouling?. (5th October 2015) - Davenport, John
Abstract : The behavioural responses of scavenging animals to mackerel ( Scomber scombrus ) baits were studied by short-term video photography in shallow water (16–18 m depth) at Lough Hyne, Ireland. Earliest arrivals (after seconds/minutes) at baits were small fish or swimming crabs ( Liocarcinus depurator ), followed by crawling portunid crabs. After tens of minutes, juvenile whelks 2–4 mm shell length ( Nassarius reticulatus and/or Nassarius incrassatus ) sometimes arrived to feed. They moved at a mean speed of 1.24 (SD 0.392) mm s −1 . After tens of minutes or hours, single large scavengers arrived, consuming most of the bait; the most common of these were Cancer pagurus that fed in a wasteful fashion, generating large quantities of mackerel scraps. Cancer pagurus moved into view at a mean speed of 48.7 (SD 16.9) mm s −1 (39 times the whelk speed). A single individual of C. pagurus (197 mm carapace width) arrived at a bait carrying 24 juvenile whelks on the dorsal surface of its carapace. No whelks were present on walking legs or chelipeds. The crab fed for 6.8 min and 3 whelks fell off before it departed. The nature of this crab/whelk association is discussed; on balance it appears that it is a previously unreported example of phoresy/phoresis. No whelks were observed being carried by other edible crabs or upon large numbers of scavenging portunid crabs.