Absorption and gut passage time of microalgae in a suspension feeder- an evaluation of the 51Cr 14C twin tracer technique

Abstract

The bivalve Mercenaria rnercenaria was pulse-fed labelled microalgae in experiments designed to test the applicability of the SICr: "C twin tracer technique to the study of food absorption in a suspension feeder. Absorption efficiencies of the chlorophyte Pseudoisochrysis paradoxa using Conover's ash-ratio method and the tracer technique were in good agreement. Clams absorbed approximately 14 % of the 51Cr ingested. An assumption of the radiotracer method is that 51Cr and 14C move along the gut at similar rates. The gut passage times of the 2 isotopes differed significantly, however, when clams were fed P. paradoxa, a 'good' food source: the gut residence time of "C was greater than that of 51Cr. Therefore, analysis of a single faecal subsample can cause significant error in the calculated absorption efficiency. The value will be overestimated or underestimated depending on whether the faeces are subsampled early or late, respectively, after transfer of the animals to unlabelled food. Therefore, pulse-chasing, or recovery of faeces over a fairly extended period of time (to be determined for any given experimental conditions) is strongly recommended. Examination of the timecourse of 14C egestion revealed that the gut passage time of P. paradoxa, which was absorbed with high (82 % ) efficiency, was significantly greater than that of 2 chlorophytes (Nannochloris atomus and Stichococcus sp.) and 2 cyanobacteria of the genus Synechococcus, which are inefficiently utilized by M. mercenan'a. The study provides evidence that clams are able to sort different algal species in their passage through the gut. Control of gut clearance rates, through more rapid elimination of those algal species which are also poorly utilized, may contribute to the species' adaptive strategy.

Assimilation of trace elements and carbon by the mussel Mytilus edulis: Effects of food composition

“…Gut passage time-Several studies have shown food selectivity in the stomach and differential egestion of unassimilable particles after ingestion (Purchon 1977;Bricelj et al 1984;Shumway et al 1985). Shumway et al (1985), for example, demonstrated that a cryptomond flagellate was preferentially absorbed in the bivalve gut compared with a dinoflagellate and a diatom of similar size, Consequently, selective mechanisms in the stomach may affect organic enrichment in the particles entering the digestive tubules (Bayne 1993).…”

“…gravimetric and radiotracer) or by the ratio method 1:i.e. radiotracer and ash ratio) (Conover 1966;Calow and Fletcher 1972;Bricelj et al 1984). Each method has advantages and disadvantages.…”

“…C AEs calculated by the two methods were comparable, suggesting that both can be applied to study C assimilation in M. edulis. Our mass balance method did not take the respiratory loss of 14C into account, but this component is generally considered to be small in the short-term energetic budget of ingested 14C (< 8% of total ingestion C, Bricelj et al 1984;Kreeger 1993). Application of noninvasive gamma-emitting radiotracer techniques to study trace element assimilation in individual mussels allows AEs to be directly computed, assuming that digestion and assimilation are completed at 72 h. Furthermore, the pulse-chase feeding technique ensures that the radioactive feeding period is shorter than the gut passage of ingested food materials (i.e.…”

Energy budgets of latitudinally separated Scottolana canadensis (Copepoda: Harpacticoida)

“…To determine the assimilation efficiency of I. galbana by S. canadensis, we fed copepods algae that were doubly labeled in a two-step procedure with 14C and 51Cr (Calow and Fletcher 1972;Bricelj et al 1984). Primarily gravid females from ME and FL (1984) held at 20°C for l-2 months were used in the experiments.…”

Phytoplankton Community Structure Based on Photopigment Markers in a Mid-Atlantic U.S. Coastal Lagoon: Significance for Hard-Clam Production

“…Laboratory studies have shown that species of cyanobacteria and chlorophytes, including Chlorella spp., Nannochloris spp., and Synechococcus sp., provide an inadequate food source for juvenile hard clams because of low retention and absorption efficiencies (Bass, Malouf, and Shumway, 1990;Bricelj, Bass, and Lopez, 1984).…”