Effects of the gem clam Gemma gemma on early post-settlement emigration, growth and survival of the hard clam Mercenaria mercenaria

Abstract

Hard clams emigrated more in the presence of G. gemma than in its absence. The overall effect of reduced food was increased emigration. Presence of G. gemma in sand enhanced hard clam growth while not affecting survival, but in muddy sand growth and survival decreased. Hard clams grew best in muddy sand without gem clams. Hard clams grew faster in shallower sediments and slower with addition of G. gemma biodeposits. Undisturbed post-settlement M. mercenaria grow more slowly than they are capable of because they spend part of the time buried, presumably to avoid surface predators. Clams that are kept near the sediment surface, either because of sedimentary properties of interaction with spatial competitors, grow considerably faster than undisturbed clams in sand. This interpretation implies a trade-off between opposing selective pressures such that clams partition time between the necessary risk of feeding and the safe but energetically unprofitable sub-surface refuge from predation. -from Authors