Effects of baitworm digging on the soft-shelled clam, Mya arenaria, inMaine: Shell damage and exposure on the sediment surface

摘要

Experiments conducted during the fall of 1997 on an intertidal flat in Maine determined the extent of shell damage and exposure of Mya arenaria on the sediment surface resulting from commercial bloodworm (Glycera dibranchiata) digging. We conservatively estimate that worm diggers dig up and expose on the sediment surface approximately 6% of the greater than 2 mm fraction of the clam population each time they turn over the sediment. Twenty percent of the clams had at least one valve damaged. Fifteen percent of intact clams exposed were found with their siphon up (normal living position), 41% with their siphon down, and 44% were horizontal on the sediment surface. Large clams (5.7 cm average shell length) placed on the sediment surface in the siphon up position reburied faster and to greater depths than those in horizontal or inverted positions. Small clams (2.7 cm shell length) buried faster than large clams, and those placed horizontally or with their siphons up reburied faster than clams placed with their siphons down. We detected no difference in reburial patterns between large clams exposed on undug and recently dug sediment. Our recovery of large clams after 10 days, however, was much greater (91.8%) from undug sediment than dug sediment (59.4%) and we found twice as many clam shells exhibiting evidence of predation in the dug than the undug area. Only about 50% of the small clams were recovered live. Shell damage of recovered dead clams indicated that predators consumed some missing clams. Our results suggest that baitworm digging negatively affects the survival of Mya arenaria by directly damaging shells and by exposing clams to increased risk of predation.