Effects of food quality on the particle handling time in bivalves

Suspension-feeding bivalves may assume a large ecological role by linking benthic and pelagic systems. Therefore, a knowledge of feeding processes is necessary to fully understand bivalve dominated environments. In this study, we examined the pallial cavity residence time for Mytilus edulis and Crassostrea virginica. By measuring residence times and subtracting previously calculated particle transport rates found on the gills of mussels and oysters, handling time on the labial palps can be determined. Bivalves were offered one of three food types: Rhodomonas lens cells, Spartina alterniflora particles, or a 50/50 mixture of both. Once actively feeding, bivalves were delivered 10 mu m polystyrene beads as a tracer and feeding continued. Bivalves were sampled at 30 s intervals for 0 to 150 s and placed in liquid nitrogen, ensuring the cessation of particle transport. Digestive systems were then isolated and examined for the presence of tracer beads. For mussels, it appears that food quality has little effect on handling time. At the 30 s interval, 10-30% of the animals had tracer beads in their gut, increasing to 90% by the 150 s time interval. Assuming a residence time of 60s (25-50% of animals) for mussels with average gill lengths of 2.8 cm (used in our study), handling time on the palps would be 12 s. Therefore, estimated labial palp transport rates are indicative of slurry as opposed to mucus transport. Results of this and parallel studies with oysters will be utilized to create a numeric model of pallial processes using the modeling software Stella.