Short-term hypoxia modulates Rapana venosa (Muricidae) prey preference in Adriatic lagoons

We studied the effect of short-term hypoxia on predation by the non-native rapa whelk (Rapana venosa) on the three most common bivalve prey in northern Adriatic lagoons: the non-native ark shell (Scapharca inaequivalvis) and Manila clam (Tapes philippinarum), and the native cockle Cerastoderma glaucum. In mesocosm experiments, bivalves were offered to predator as single prey, and as multiple choice of prey. Bivalve prey showed behavioural responses when exposed to short-term hypoxia. Under normoxia, prey were consumed in almost equal numbers when offered separately, but when choice was offered to the predator R. venosa showed a marked preference for S. inaequivalvis. Short-term hypoxia increased the vulnerability of T. philippinarum, and, consequently, rapa whelks modified their predatory behaviour and switched their preference to T. philippinarum. We hypothesize this to be a case of environmentally-mediated, non-reciprocal indirect interaction between the two non-native prey species, whose causes are based upon differences in specific traits of prey. Hypoxia may facilitate the coexistence of the two non-native bivalves via predator switching. The native cockle seems the net loser of the game.