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

Abstract

Pearl oysters are farmed in oligotrophic tropical atoll lagoons where planktonic communities are dominated by production from cyanobacteria smaller than 2 µm. Paradoxically, the pearl oyster Pinctada margaritifera only retains particles larger than 2 µm. In this study, we assess the relative contribution of hetero/mixotrophic microbiota to the available planktonic resource. In Takapoto Atoll, picocyanobacteria are the dominant biomass (20 µg C l -1 ). The carbon biomass of ciliates and dinoflagellates ranges from 1 to 24 and 0.5 to 5 µg C l -1 respectively, with a mean of 6 µg C l -1 for ciliates and 2 µg C l -1 for dinoflagellates. The possible retention by P. margaritifera on a natural protist suspension was investigated. Due to its high clearance rates (ca 20 l h -1 g -1 ) the pearl oyster retained 85 µg C h -1 g -1 from ciliates and 65 µg C h -1 g -1 from dinoflagellates. Conversely, cyanobacteria were not efficiently retained by the bivalve and did not efficiently contribute to its diet. From our experiments, we concluded that hetero/mixotrophic protists rapidly and efficiently process the picoplanktonic resource towards filter-feeders, particularly pearl oysters. KEY WORDS: Protists · Atoll lagoon · Pearl oysters · Pinctada margaritifera · Picoplankton · Trophic resourceResale or republication not permitted without written consent of the publisher

Physical and chemical control of the phytoplankton of Ahe lagoon, French Polynesia

“…There is no available data to conclude on the positive effect of feeder on phytoplankton; conversely, recent work conducted in Ahe by Fournier et al (2012) on pearl oyster grazing has found that the diet of P. margaritifera is composed mainly of heterotrophic (without Chl a) nano-and micro-plankton and not of phytoplankton. The negligible influence of the oysters on the planktonic network and the importance of heterotrophic protists in the diet of P. margaritifera have also been formally demonstrated in Takapoto atoll by Niquil et al (2001) and by Loret et al (2000), respectively.…”

Assimilation of carbon from a rotifer by the mussels Mytilus edulis and Perna viridis: a potential food-web link

“…The last resource includes heterotrophic nanoflagellates (3 to 8 µm) (Kreeger & Newell 2001), ciliates (20 µm) (Le Gall et al 1997), protists (30 to 136 µm) (Loret et al 2000), rotifers (140 to 256 µm) (this study, Wong et al 2003), as well as other zooplankton (138 to 518 µm, Dupuy et al 2000b, 100 to 1000 µm, Davenport et al 2000), and coccasionally animals < 3000 to 6000 µm (Davenport et al 2000). This enlarged food spectrum of bivalves suggests that they are usually generalist grazers (Asmus & Asmus 1991).…”

“…It can be predicted that nano-and microzooplankton may play a more important role in the aquatic environment since they are much more abundant than mesozooplankton in numbers and biomass (Stelfox et al 1999). Of particular importance are the ciliates and flagellates, which can not only be directly consumed by bivalves (Dupuy et al 2000a,b), but also act as a trophic link between bacterioplankton and benthic suspension feeders (Le Gall et al 1997, Dupuy et al 1999, Loret et al 2000.…”

In situ evidence for pre-capture qualitative selection in the tropical bivalve Lithophaga simplex

“…A. zebra, but not P. imbricata, demonstrated particle selection, rejecting (in the pseudofeces) material with significantly higher carbon and lower nitrogen concentrations, thereby increasing the quality of material ingested by approximately 31%. Qualitative selection in the tropical pearl oyster P. margaritifera has also been inferred from gut content analysis (Loret et al 2000); however, the techniques of both studies do not allow the distinction between pre-and post-capture selection.…”