Preferential ingestion of organic material by the American oyster Crassostrea virginica

Abstract

Using an artificial diet, composed of silt < 32 p in diameter and the alga Tetraselmis suecica, it was demonstrated that the oyster Crassostrea virginica could significantly reduce the concentration of algae voided in the pseudofaeces (measured as extracted chlorophyll pigment) by over 50 %, compared to levels in the food. More importantly, it was also shown that for C. virginica fed natural seston at concentrations between 4 to 20 mg I-', the proportion of energy, carbon and nitrogen voided in the pseudofaeces could also be reduced significantly compared to that in the food. As the organic material in natural seston is from a wide range of sources -e.g. phytoplankton of different sizes, bacteria, detritus particles, etc. -these results indicate that C. virginica has a well developed ability to ingest preferentially various types of organic material and to reject other particles as pseudofaeces. This discriminatory mechanism must be able to operate on individual particles despite the fact that they are bound in viscous mucus. We hypothesise (based on literature information for the properties of molluscan mucus) that the viscosity of the mucus in which the food particles are entrapped may be significantly reduced by the ciliary action on the ridged surfaces of the opposed labial palps. This reduced viscosity mucus is possibly moved to the free edge of the palp where, with a cessation of the mechanical stimulation, it regains its original viscosity. The individual particles may then be subject to chemical testing by chemoreceptors which determine whether a particle is moved over the palp ridge to the mouth or is admitted to the deep rejection tracts. These rejected particles move to the free edge of the palps where they are re-incorporated in the mucus and rejected as pseudofaeces.

Feeding ecology of the mangrove oyster, &lt;i&gt;Crassostrea gasar&lt;/i&gt; (Dautzenberg, 1891) in traditional farming at the coastal zone of Benin, West Africa

“…Though consuming about thirty (30) genus of phytoplankton, Melosira (Diatomophycae), Polycystis (Chlorophycae) and Crucigenia (Scenedesmacae) remained the dominant algae consumed and accounting for 23.77%, 17.19%, and 13.77%, respectively. This trophic specialization probably results from anatomical structure, mainly the presence of gills which facilitate the filtering of numeric phytoplankton taxa [31]. As reported by Newell and Langdon [32], in the water column, planktons and particles are drawn on the gills by the motion of small cilia.…”

“…i As a result, C. gasar colonizes various brackish habitats of temperate to sub-tropical environments and are found abundantly in seashores, shallow bays, lagoons, estuaries, and coastal waters [44][45][46]. This trophic plasticity behavior probably results from the specialized morphological structure of C. gasar, mainly the presence of gills which facilitate the filtering of numeric phytoplankton [31].…”

“…Discrimination of the nutritional quality of ingested foods: Crassostrea species are sessile epibenthic bivalves confined to the bottom and not capable to move for foraging [31,49]. Probably, to adapt to this benthicmuddy environment and to increase survival, this species has evolved a specialized feeding mechanism and strategy to retrieve only needed nutrients for growth and development and to reject awful and non-digestible foods.…”

Croissance prolongée de la diatomée marine Phaeodactylum tricornutum en milieu contaminé par le chlorure de tributylétain : conséquence sur le biotransfert du polluant

“…Dans la mesure où la culture continue reflète davantage le milieu naturel (RHEE, 1980), la croissance persistante de micro-algues contaminées constitue un fait nouveau qui évoque la possibilité d'un biotransfert important du polluant à travers la chaîne alimentaire marine. Ceci vise plus particulièrement les organismes filtreurs planctoniques qui sélectionnent le matériel particulaire vivant (POULET et MARSOT, 1978 ;NEWELL et JORDAN, 1983), et les espèces benthiques qui concentrent plusieurs milliers de fois l'organoétain sous sa forme toxique (WALDOCK et THAIN, 1983 ;ZUOLIAN et JENSEN, 1989 ;HIGASHIYAMA ef al., 1991).…”

Phytoplankton distribution and oyster,Ostrea chilensis(Philippi 1845), growth at Putemún Channel, southern Chile

“…This inverse relationship between food availability (phytoplankton biomass) and TPM, could be caused by a dilution of the organic particles by resuspended inorganic sediment as discussed by Preston & Prodduturu (1992) and Barille et al (1997). Numerous authors have claimed that bivalves are able to preferentially ingest organic matter (Kierboe & M0hlenberg 1981;Newell & Jordan 1983;Bayne et al 1989;Newell et al 1989). Pseudofaeces production represents a mechanism for selecting and separating material of high nutritional quality (POM) from material less rich in organic matter (PIM) (Iglesias et al 1992;Bayne et al 1993;).…”