Phytoplankton composition and selective feeding of the pearl oyster Pinctada margaritifera in the Takapoto lagoon (Tuamotu Archipelago, French Polynesia):in situ study using optical microscopy and HPLC pigment analysis

Abstract

The in situ diet of the pearl oyster Pinctada margaritifera was determined in the lagoon of Takapoto Atoll by comparing the phytoplankton composition of water and bivalve gut contents using 2 different methods, optical microscopy and HPLC pigment analysis. In order to evaluate the available food resources for pearl oysters in the water column, a new method for estimating the pigment/chlorophyll a (chl a) ratio (based on an inverse analysis) was developed which allowed us to determine the contribution of the main phytoplanktonic groups in terms of chl a. In the water, picocyanobacteria and nanoflagellates predominated, the latter being mainly chlorophytes and prymnesiophytes. Comparisons between the results obtained by the 2 methods of investigation indicated that most of the dinoflagellates are unpigmented and, therefore, heterotrophic. An examination of the gut contents showed that picocyanobacteria were only weakly ingested by the oyster and, thus, nanoflagellates constituted the main food resource. Cryptophytes, although poorly represented in the water, were preferentially ingested. Chlorophytes were inefficiently hgested since they were found alive and motile in the faeces of the oyster. The ecological implications of this feeding behaviour are discussed.

Numerical analysis of the food web of an intertidal mudflat ecosystem on the Atlantic coast of France

“…Moreover, suspension feeders use pseudofaeces to enrich the organic fraction of their diet (Deslous-Paoli et al 1992, Iglesias et al 1992, Bayne et al 1993, Barillé et al 1997) and suspension feeding is a 'highly selective' process (Shumway et al 1985, Graf & Rosenberg 1997. For example, Crassostrea gigas feeds selectively upon the microphytobenthic food supply (Cognie et al 2001) and the pearl oyster Pinctada margaritifera selects its prey on both size and taxonomic criteria (Loret et al 2000). Considering that filter feeders may actively select living material for ingestion, the limited uptake of detritus in our results should be realistic.…”

Heterotrophic protists as a trophic link between picocyanobacteria and the pearl oyster Pinctada margaritifera in the Takapoto lagoon (Tuamotu Archipelago, French Polynesia)

“…The fact that the pearl oyster retains I. galbana and phagotrophic protists with the same efficiency indicates that the autotrophic or heterotrophic nature of the prey does not influence retention by the oyster. However, despite this variety of available food sources, it was recently demonstrated that pearl oysters exert selective feeding, especially on cryptophytes (Loret et al 2000).…”

Routine quantification of phytoplankton groups—microscopy or pigment analyses?

“…In contrast, analyses of phytoplankton pigments by HPLC are more reproducible than microscopic analyses (Schlüter et al 2000), and are increasingly being used for determining the composition of phytoplankton communities (Tester et al 1995, Loret et al 2000. The CHEMTAX program was developed by Mackey et al (1996) as a data treatment programme for calculating algal class biomass as chl a from the concentrations of the phytoplankton accessory pigments determined by HPLC.…”