ONTOGENIC CHANGES IN MICROHABITAT DISTRIBUTION OF JUVENILE BAY SCALLOPS, ARGOPECTEN-IRRADIANS-IRRADIANS (L), IN EELGRASS BEDS, AND THEIR POTENTIAL SIGNIFICANCE TO EARLY RECRUITMENT

Ontogenetic changes in the vertical distribution of a cohort of juveni le bay scallops, Argopecten irradians, on eelgrass, Zostera marina, we re followed throughout the summer and early fall in two Long Island em bayments (New York, USA). Despite site-specific differences in eelgras s height and density, more than 95% of post-settlement scallops remain ed attached above the bottom until they reached a shell height of abou t 11 mm. Over a 5-week period, scallops gradually relocated until, at a mean size of 31 mm, all occurred on the bottom. The decline in perce nt attachment coincided with a 5-fold increase (from 16 to 84 mumoles min-1 g muscle dry wt-1) in the activity of octopine dehydrogenase (pr oposed here as an index of the scallops' capacity for burst swimming a ctivity), and in maximum rate of increase in the shell aspect ratio. W hile attached to eelgrass, scallops were nonuniformly distributed, wit h greatest concentration at mid-canopy. Following disturbance, they ra pidly regained above-ground position, attaining asymptotic heights wit hin 3-10 h. This and prior studies suggest that the climbing behavior of the bay scallop is an adaptive response to high predation pressure at small sizes. Enhanced scope for activity (predator avoidance) may e nhance survival of scallops at intermediate sizes, when they become to o heavy to maintain elevation but have not yet attained effective refu ge in size.