SHELL-CRUSHING PREDATION ON THE ANTARCTIC SCALLOP, ADAMUSSIUM COLBECKI

One of the most fundamental changes predicted to occur under global change scenarios for Antarctica is the invasion of durophagous (shell-crushing) predators, such as decapod crustaceans, which have not been present in Antarctica's waters since the warmer Eocene Period, over 30 million years ago. Despite this looming global climate change situation, little is known about how predators structure subtidal communities in Antarctica, especially in regard to predation on shelled prey. Recently, brachiopod shells from waters off the Antarctic Peninsula were reported to have a very low frequency of shell repair, indicating that durophagy can occur. But does durophagy occur on other shelled organisms, such as epifaunal molluscs? And, if it does, are repair frequencies similar to those reported for brachiopods from the Antarctic Peninsula?

To assess the current shell repair frequencies on epifaunal bivalves, shells (n = 623 valves) of the Antarctic Scallop, Adamussium colbecki (from five sites within and adjacent to Explorers Cove, McMurdo Sound, Antarctica) were examined for damage and subsequent repair. Repairs were consistent with predatory damage: valves had stereotypic damage patterns; repairs had similar distribution on each valve; and large-sized scallops were selected. Frequency of repair varied between 4% and 26% for the five sites and depths (6-24.4 m), with a mean of 10%. Incidence of repair within Explorers Cove was not significantly different with depth or among sites (alpha = 0.05). However, one Explorers Cove site (24 m, Ice Cliff) was just barely significant from an adjacent 24 m site (Ferrar Glacier), which had the highest repair frequencies of all the sites (26%; P = 0.049). When repair was compared among adult versus juvenile stages of each valve, the highest frequency of repair occurred during the adult stage (6-10 cm in valve length). These mean repair frequencies are similar to those reported from infaunal bivalves in cool temperate regions, much higher than frequencies reported for epifaunal brachiopods from the Antarctic Peninsula, and much lower than frequencies reported for Patagonian scallops, where shell-crushing crabs occur. Durophagy does occur in Antarctica's continental waters, indicating that the arrival of shell-crushing crustaceans may not bode well for epifaunal scallops.