Experimental study of the effect of kaolinite on the ingestion and the absorption of monospecific suspensions of Pavlova lutheri by the filter-feeding bivalve Venus verrucosa

We investigated the ingestion and the absorption of the filter-feeding biva lve Venus verrucosa Linne fed on Pavlova lutheri Droop in the presence of d ifferent concentrations of kaolinite (i.e., between 0 and 50 mg.l(-1)). We used C-14-sodium bicarbonate to label the algae. In the presence of bivalve s, the exchanges of radioactivity between compartments were always dominate d by the transfer between POM and bivalves. However, there were significant differences in radioactivity partitioning among compartments depending on the concentration of kaolinite. The observed transfers resulted from the in teractions between ingestion, absorption, biodeposition, and recycling of b iodeposits. The coexistence of these processes did not allow to determine d irectly ingestion rates and absorption efficiencies, which required the use of mathematical modelling. The model used during the present study is iden tical to the one previously designed to describe the utilisation of a suspe nsion of Escherischia coli by Venus verrucosa. It simulates the exchanges o f radioactivity between compartments and allows the quantification of inges tion and absorption. It is complicated by the occurrence of pseudofaeces pr oduction at the highest kaolinite concentration. Our results show no signif icant differences in both ingestion rates (10 mgDW.h(-1) at 0 and 5 mg.l(-1 ) of kaolinite) and absorption efficiencies (about 57 % at 0 and 5 mg.l(-1) of kaolinite) below the threshold of pseudofaeces production. Filtration a nd thus ingestion rates were significantly reduced for a kaolinite concentr ations of 50 mg.l(-1). Apparent absorption efficiency was also much lower ( about 34 %) during the 50 mg.l(-1) experiment. In addition, the highest con centration of kaolinite induced higher biodeposition and recycling rates of labelled material. These results are discussed in view of the existing lit erature.