The influence of algal concentration and body size on filtration and ingestion rates of the clam Tapes decussatus (L.) (Mollusca: Bivalvia)

Abstract

The filtration and ingestion rates of Tapes decussatus (L.) (12.5-32.5 mm in size), collected from Timsah Lake, Suez Canal, Egypt in 1993, were determined in relation to food concentration and clam dry tissue weight. Suspensions of the unicellular green alga Dunaliella marina, in concentrations ranging from 103 to 105 cells ml-1, were provided as food. The filtration rate (F, ml h-1 clam -1) and the weight-specific filtration rate (F“, ml h-1 mg-1 dry tissue weight) generally decreased with increased algal concentration following the allometric equations F= 2736.8 W-0,183 and F’= 12.6 W-0.182 The amount of water filtered free of particles by a clam of 210 mg dry tissue weight was in the ratio 1:1.4:2.3 with decreasing algal concentrations at 105, 104 and 103 cells ml-1, respectively. In contrast, the ingestion rate (I, cells h-1 clam-1) and weight-specific ingestion rate (I“, cells h-1 mg-1 dry tissue weight), generally increased with increased algal cell concentration following the allometric equations I= 0.01 W0.87 and I= 0.005 W0.88, where W is the algal cell concentration per ml. When the clams were fed on 105 cells ml-1, F and I increased with increased body size following the equations F = 7.5 W0.74 and I“= 8.89 W0.63. Otherwise, F“ and I“ decreased with increased body size following the equations F“ 7.5 W-0.25 and I“ 698.6 W-0.36, where W is the dry tissue weight in mg.