ALBERT

Notes: Abstract Feeding responses of the tentaculate depositfeeding polychaeteEupolymnia nebulosa (Montagu) were studied by measuring rates of uptake of three different14C-labelled diatoms (unialgal cultures ofNavicula incerta Grunow,Nitzschia acicularis Wm Smith, andNitzschia sp.). Worms used during this study were collected in the harbor of Port-Vendre (Western Mediterranean) during August 1986 (immature worms) and December 1987 (mature worms). Uptake rates were affected both by the length of the experiments and by the nature of the food offered. The highest rate of uptake (2.98 10−4 mg ashfree dry wt of algae mg−1 dry wt of worms h−1) was obtained during short-term experiments (4 h) with the smallest diatom (Nitzschia sp.). The lowest rate of uptake (0.21 10−4 mg ash-free dry wt of algae mg−1 dry wt of worms h−1) was also obtained withNitzschia sp., but for a long-term (48 h) experiment. There was no significant difference between rates of uptake of immature and mature worms.

Notes: Abstract The present study tested the utilization of dead microbial biomass by two benthic deposit-feeders:Abra alba (Wood) (Mollusca: Bivalvia) andEupolymnia nebulosa (Montagu) (Annelida: Polychaeta). Clams were collected in the Canet lagoon during spring 1989. Worms were collected in the Port-Vendres harbour during spring 1989. The14C-labelled (glutamic acid, 24 h) sediment used during the study was sterilized with 1% chloroform, washed with sterile seawater, and dried (60°C; 48 h). This sterilisation procedure, called “fumigation” is the least harmful to the sediment (Novitsky 1986). Both clams and worms were incubated in the presence of the fumigated sediment for 5, 10, 20, and 50 h. At the end of each experiment we recorded the radioactivity in four compartments: (1) sediment, (2) dissolved organic matter (DOM), (3) CO2, and (4) animals. The radioactivity of the sediment was subdivided into five fractions: (i) soluble in 2N HCl, (ii) soluble in hot 5% trichloroacetic acid (TCA), (iii) soluble in 1N NaOH, (iv) soluble in hot 6N HCl, (v) residual (after combustion in a Leco carbon analyser). In the first set of experiments, after 20 h of incubation, 5.4 and 4.7% of the total radioactivity was taken up by clams and worms, respectively. However, a model revealed that this uptake could have been correlated with the release of radiolabelled DOM (33% of total radioactivity during the first 5 h). In order to test this assumption, we used the same protocol with three additional washes of the fumigated sediment. This resulted in a significantly lower uptake by the clams (1.9% of the total radioactivity byt = 50 h), whereas the worms exhibited an uptake similar to that in the initial experiment (5.1% of total radioactivity byt = 50 h). These results underline the importance of considering interactions with DOM when applying radiotracer techniques to the study of benthic food chains. The average ingestion rates of fumigated sediment byA. alba andE. nebulosa were 5.2 10−2 mg sediment dry wt mg−1 clam h−1 and 3.5 10−2 mg sediment dry wt mg−1 worm h−1, respectively, which is comparable to previous data reported for other deposit-feeding bivalves and polychaetes feeding on natural sediment or detritus. The low radioactivity recorded for CO2 together with the similarity of the changes in the partitioning of the radioactivity within the sediment between control experiments and experiments carried out in the presence of clams or worms suggest low assimilation efficiencies. Therefore, the present study supports the fact that dead microbial biomass does not constitute an important food source for benthic deposit-feeders.

Notes: Abstract This paper describes the mathematical model used to compute the filtration and assimilation rates of two filter-feeding bivalves, Venus verrucosa and Mytilus galloprovincialis fed on the enteric bacteria Escherichia coli. The model initially consisted of six compartments: bivalves, bacteria, dissolved organic matter (DOM), CO2, biodeposits, and resuspended biodeposits. We introduced three second-order time-delays to account for the time lags between ingestion of radioactive materials and (1) the production of radioactive biodeposits, (2) the production of radioactive DOM, and (3) the production of radioactive CO2 by the bivalves. These delays resulted in the subdivision of the bivalves compartment into three subcompartments: Bivalves 1, Bivalves 2, Bivalves 3. The model simulates the exchanges of radioactivity between compartments, and allows the quantification of the radioactivity corresponding to compartments that cannot be directly measured (i.e., bacteria and biodeposits). Our results show that M. galloprovincialis ingests E. coli more quickly than does V. verrucosa (kinetic coefficients of 0.280 and 0.120, respectively). Neither bivalve seems able to efficiently assimilate E. coli. The assimilation rates of V. verrucosa and M. galloprovincialis are between 11.1 and 20.4%, and 7.5 and 14.8%, respectively. Because of the low assimilation rates recorded during this study, because of the resuspension of the biodeposits produced, and because of the presence of culturable E. coli in biodeposits of both bivalves, our conclusions are that: (1) filter-feeding bivalves are probably inefficient in purifying seawater polluted by the tested strain of E. coli, and (2) as opposed to marine bacteria and other previously tested enteric bacteria, the strain of E. coli used during the present study probably does not constitute a suitable food source for filter-feeding bivalves.

Notes: Abstract We investigated the filtration and utilization of the enteric bacteria Escherichia coli by two suspensionfeeding bivalves, Venus verrucosa (Linné), collected, during April 1990, in Port-Vendres harbour (France), and Mytilus galloprovincialis (Lamarck) collected from rearing units in the bay of Banyuls-sur-mer during June 1990. Because of a significant decrease in the concentration of culturable E. coli in filtered seawater, we used 14C glutamic acid to label the bacteria. Labelling efficiency was low (20%) compared to the 30% reported for the marine bacteria Lactobacillus sp. by Amouroux (1982). However, the labelling by this radioisotope was very stable, enabling its use to monitor filtration. Concentrations of culturable E. coli decreased more rapidly in the presence of M. galloprovincialis than in the presence of V. verrucosa. In both bivalve species, changes of radioactivity within the bivalve, particulate organic matter (POM), dissolved organic matter (DOM) and CO2 compartments were similar and resulted from the interaction of several processes: filtration, biodeposition, and recycling. This interaction complicates the determination of the actual ingestion and assimilation rates, and necessitates the use of mathematical modelling.

Notes: Abstract The utilisation of the exudates of bacteria (Lactobacillus sp.) and phytoplankton (Pavlova lutheri) by the clam Venus verrucosa Linné under identical experimental conditions was studied. 61.7% of the bacterial exudates were consumed but only 19.9% of the algal exudates. V. verrucosa would seem to assimilate bacterial products more easily than phytoplankton exudates. The study was performed in 1980.

Notes: Abstract The utilisation of a viable bacterial suspension (Lactobacillus sp.) by the clamVenus verrucosa Linné, 1767 has been investigated as a function of time. The clams filtered and ingested 95% of the suspension within 2 h. Radioactivity recovered from the soft-body of the clams measured 51% of the total radioactivity introduced at the start of the experiment after 2.5 h, 48.8% after 10 h, and 39.9% after 40 h. The dissolved organic matter remained nearly constant, with 27.5% after 2.5 h, 24.4% after 10 h, and 29.8% after 40 h. The faeces produced increased from 13.2% after 2.5 h to 21.9% after 10 h, and decreased until 40 h with 16.2%. The carbon-dioxide respired increased slowly to 5% after 40 h. These data on the functioning of the different compartments suggest an important recycling of the metabolic products of the bivalves by the bacteria of the suspension, demonstrating the role of bacteria as food for bivalves.

Notes: Abstract Following a previous study, this paper deals with the utilisation of a phytoplankton suspension (Pavlova lutheri) by the clam Venus verrucosa Linné, 1767 as a function of time. Experimental clams filtered and ingested 100% of the suspension after 2 h. The radioactivity recovered in the whole soft body of the clams was 83.8% after 2 h, 66.0% after 10 h and 46.0% after 41 h. The faeces contained 13.7% after 3 h and 34.3% after 41 h. Carbon-dioxide radioactivity (gas plus dissolved) increased slowly to 12.4% after 41 h. When the water was not changed after 17 h, the clams reabsorbed a great part of their dissolved products and faeces. Under these latter conditions the radioactivity recovered from the whole soft body of the clams was roughly the same as that recovered after the start of the experiment. The aim of this study was the comparison of the consumption of two kinds of food: bacteria and phytoplankton. The work was carried out over three years, from 1977 to 1980.