Differential utilization of species of phytoplankton by the mussel Mytilus edulis

摘要

The phytoplankton community includes a variety of species differing in size and other structural characteristics that are likely subjected to a differential processing by filter-feeding bivalves. These processes would include: (a) The differential retention in the gills, (b) the preingestive selection at the level of gills and palps associated to the process of pseudofaeces formation, and (c) the selective digestion of phytoplankton cells ingested. The present experiments were conducted using a mixed diet of a diatom (Phaeodacolum tricornuttum) and a naked flagellate (Tetraselmis suecica) at low particle concentration (below the pseudofaeces threshold) in order to check for the differential retention and/or digestive selection of any microalgae component by the mussel Mytilus edulis. To this effect, changes in the proportion of both components between the feeding suspensions, stomach contents and faeces over time were ascertained. Simultaneous clearance rate measurements allowed quantifying the ingestion rate of each microalgal component which, compared with the amounts retained inside the stomach, served to compute their respective rates of gut processing. Filtering activity reduced the abundance of P. tricornutum (reduced Phaeodactylum/Tetraselmis (P:T) ratio) in the surrounding water, but differences between the control and remaining water were found to be non-significant: consequently, we failed to demonstrate a differential retention by the gill of any component of the diet. P:T ratio was greatly reduced in the stomach contents and, to a lesser extent, in faecal particles, for comparison with particle suspension in controls and remaining water; these differences being significant. This result strongly suggests the preferential utilization of the diatom within the stomach of mussels. The rates of evacuation from the stomach were clearly different, showing a fast and slow component represented by P tricornutum and T suecica, respectively. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved. [References: 28]