Mucous-cord secretion for drifting by the clam <i>Meretrix lusoria </i>(Veneridae) under varying light/dark and submergence/exposure conditions

Abstract

Both juveniles and adults of the venerid clam Meretrix lusoria secrete a transparent mucous cord and drift over tidal flats, using the mucous cord as a sail. To clarify the ecological roles of mucous-cord secretion, the conditions affecting secretion were examined in the laboratory using clams burrowing in sand. Darkness and sand exposure played important roles in mucous-cord secretion: Under a 12-h : 12-h Light/Dark cycle with continuous sand submergence, 84% of mucous-cord secretions occurred in the dark. Under a 6-h : 6-h Submergence/Exposure cycle in continuous darkness, 79% of mucous-cord secretions occurred within 2 h of the submergence. Since clams secreted mucous cords without being exposed to adverse conditions such as hypoxic waters, it appears that mucouscord drifting in the field does not necessarily serve as an escape mechanism when the clam encounters unfavorable conditions. On the contrary, it is suggested that drifting is a risk-dispersion (bet-hedging) strategy to sustain the population under the varying and unpredictable conditions of tidal flats.

Trophic cues promote secondary migrations of bivalve recruits in a highly dynamic temperate intertidal system

“…By producing byssus threads (Sigurdsson et al. ) or mucus (Nakamura ), post‐larvae increase their drag and thus increase their drift, allowing an active control of the dispersal via resuspension even under low current conditions (Lundquist et al. ).…”

“…We hypothesized that active migration behavior like bysso-pelagic drift, mucus production, and crawling could constitute a significant energetic cost for recently metamorphosed postlarvae. By producing byssus threads (Sigurdsson et al 1976) or mucus (Nakamura 2015), post-larvae increase their drag and thus increase their drift, allowing an active control of the dispersal via resuspension even under low current conditions (Lundquist et al 2004). To our knowledge, the energy costs of these behaviors have never been assessed.…”