Predation on settling bivalve larvae by benthic suspension feeders: the role of hydrodynamics and larval behaviour

Predation by the suspension-feeding infaunal bivalve Ceiastoderma edule on settling C. edule larvae was studied in a flume boundary-layer flow. The density of settled larvae was reduced by 33 % in an area of 5 cm2 enclosing individual adults. Mean survival time for competent C. edule larvae drifting over sediment populated with feeding adults (380 ind. m−2) was 64 s, and 75 % of the observed larvae were inhaled by adults. Observations of the siphonal currents produced by C. edule and the swimming behaviour of larvae were combined in a computer model to assess the importance of adult density and boundary-layer flow on the predation risk experienced by settling larvae. Survival of settling larvae decreased drastically with increasing adult density, whereas increased flow velocity caused only a slightly higher predation risk. Although reduction in larval settlement on the scale of individual adults may be small or moderate, inhalation of settling larvae by populations of resident suspension feeders may cause a significant decrease in settlement on a larger scale ( 101 to 103 m).