Filter-feeding bivalves are able to sense the presence of suspended food particles in the ambient water, and this sensitivity is reflected in the gape of the valves (Jorgensen 1975).
Next, in field studies we examined the interactions between water flow, near-bed phytoplankton biomass and valve gape opening-closing response times of mussels in a dense bed.
In another series of experiments, the valve gape opening-closing response of mussels caused by presence/absence of algal cells was also recorded during periods with continuous algal supply followed by starvation periods without algal supply.
1] (fully open mussels) to the time when the mean valve gape was reduced to 50% of the maximum registered during the preceding steady-state period.
Initially the mean valve gape decreased nearly linearly, but the closing response was faster in fed than in starved mussels.
The observed valve gape responses to presence/absence of algal cells in the ambient water shows that the valve opening/closure responses are strongly influenced by the preceding feeding conditions.
The duration of the opening response (defined as the time from readdition of algal cells after a short period of valve closure caused by stoppage of the dosing pump until the mean valve gape had increased to maximum) is shown on Figure 8.
1] responded to a slight reduction in the algal concentration by a nearly immediate reduction in valve gape (Fig.
were never exposed to such high current speeds reported to affect the valve gape of mussels (see e.
As stated by Riisgard (2001b) the valve-closing phenomenon, which has also been clearly demonstrated in the present work, represents a physiological adaptation to filter feeding in extremely meager situations, when a reduced valve gape reduces the metabolism of the mussel (Jorgensen et al.