Retention of ciliates and flagellates by the oyster Crassostrea gigas in French Atlantic coastal ponds:protists as a trophic link between bacterioplankton and benthic suspension-feeders

Abstract

Retention of ciliates and flagellates by the oyster. In order to evaluate the importance of the 'protozoan trophic link' for energy transfer from the 'microbial food web' to large benthic suspension feeders, we offered a coastal pond comn~unity of ciliates and flagellates as potential prey to the oyster Crassostrea gigas. Clearance rate, filtered particles and relative retention efficiency were evaluated. In the grazing experiment, 94 % of ciliates and 86% of flagellates (size between 4 and 72 pm), were retained by the oyster. Whatever their size, protists were similarly retained by the oyster gills. In terms of carbon, oysters retain on average 126 pg C h-' g-' dry weight, a value over 4 times h~g h e r than reported for phytoplankton. These results indicate that a field community of protists can contribute in coastal oyster rearing ponds to the energy requirements of the oyster C. gigas. We report here the first experimental ev~dence of a significant retention of a protist community by oysters, supporting the role of protists as a trophic link between picoplankton and benthic filter-feeding bivalves. The importance of phytoplankton in the nutrition of oysters is well documented , Pastoureaud et al. 1996. However, in oyster rearing environments, such as the particularly light-limited turbid estuary of Marennes-Oleron, or in coastal ponds of the Charente where nutrients are quickly exhausted, phytoplankton cannot entirely account for the energy requirements of oysters .In the oceans, more than 50% of the primary production is due to unicellular organisms less than 3 pm in size (Li et al. 1983, Glover et al. 1986), which constitutes a nutrient source of particulate and dissolved organic matter for heterotrophic organisms. Dissolved organic matter (DOM) present in coastal waters (Pomeroy & Wiebe 1993) provides a potential for high bacterial production. Thus, in the 0 Inter-Research 1999Resale of full artrcle not perrnltted

Comparison of samplers for the biological characterization of the sea surface microlayer

“…Enumeration of ciliates and flagellates-Ciliates and flagellates were fixed, stained, and enumerated according to Dupuy et al (1999). This method is a modified version of the method previously described by Haas (1982), Caron (1983), and Sherr et al (1994).…”

Importance of different size classes of phytoplankton in Beatrix Bay, Marlborough Sounds, New Zealand, and the potential implications for the aquaculture of the mussel,Perna canaliculus

“…Previous studies have indicated that particles <2 µm in diameter are generally inefficiently consumed by bivalves (Ward et al 1998;Dupuy et al 1999) and studies currently being undertaken indicate that this is also true for P. canaliculus (authors' unpubl. data).…”

“…The phytoplankton community was divided into microphytoplankton (20-200 µm), nanophytoplankton (2-20 µm), and picophytoplankton (0.2-2 µm) size classes according to the scale of Sieburth et al (1978). The nanophytoplankton (2-20 µm) were further divided into two size ranges, 2-5 and 5-20 µm, to cover feeding retention size ranges as described by Ward et al (1998) and Dupuy et al (1999).…”

In situ method for measurements of community clearance rate on shallow water bivalve populations

“…3) is in good agreement with the literature. Using an allometric exponent of 0.73 (Riisgård 1988), the clearance rate for an oyster (3.9 g) can from the literature be calculated to 10.2 L h -1 (Bougrier et al 1995), 8.2 L h -1 (Ren et al 2000), 10.8-19.4 L h -1 (Dupuy et al 1999), and for Crassostrea virginica 18.4 L h -1 (Riisgård 1988).…”