Consumption of diatoms and diatom filtrates by the tentaculate deposit-feederEupolymnia nebulosa (Annelida: Polychaeta)

Abstract

Rates of organic uptakes of three live diatoms (Nitzschia acicularis, Nitzschia sp. andNavicula incerta), and of three corresponding filtrates by the deposit-feeding polychaeteEupolymnia nebulosa (Montagu) were measured under similar experimental conditions. Worms used during this study were collected by SCUBA diving at Port-Vendres in shallow water (7 m deep) during the summer of 1986. Uptake rates of live diatoms were affected both by length of the experiments and by the nature of the food offered. The highest rate of uptake (11.8 10−4 mg algal ash-free dry wt mg−1 worm dry wt h−1) was recorded during a short-term experiment (4 h) with the smallest diatom (Nitzschia sp.). The lowest rate (1.1 10−4 mg algal ash-free dry wt mg−1 worm dry wt h−1) was recorded during a long-term experiment (48 h) with the largest diatom (Nitzschia acicularis). Filtrates ofN. acicularis were more readily utilized than those ofNitzschia sp. andNavicula incerta. Because of differences in uptake rates of algal filtrates as a function of species, it is not possible to evaluate the bias due to interaction with dissolved substances in experimental studies assessing ingestion of live benthic diatoms byE. nebulosa.