Progressive loss of byssus attachment with size in the sea scallop, Placopecten magellanicus (Gmelin)

Abstract

Byssus formation persists after metamorphosis in Placopecten magellanicus (Gmelin), but only a proportion of the population is attached at any one time; any individual alternates between attached and unattached phases. The proportion attached decreases progressively from 75% for juveniles 2–5 mm in diameter to almost zero for scallops larger than 120 mm. Time to 50% attachment ranges from 7 min for juveniles to 140 days for 100–110 mm scallops. The proportion attached at equilibrium is independent of temperature within the range 5–15 °C. Attachment in individual scallops is preceded by exploration of the substratum by the pallial tentacles of the byssus notch. During thread formation in adults, the foot is held closely apposed to the substratum for a mean duration of 25 min. The rate of byssus formation increases with temperature. Swimming and byssus formation are antagonistic behavioural patterns in P. magellanicus; swimming responses in a detached population fall off rapidly as the byssus threads are formed.