Biodeposit Production Research Articles

Rôle des interactions biotiques sur le devenir du pré-recrutement et la croissance de Pecten maximus (L.) en rade de Brest

Biotic interactions within benthic megafauna were studied from quantitative dredge samples to investigate their role in the persistence of low scallop, Pecten maximus, stocks in the Bay of Brest. The distributions of 148 species of the megafauna and of four age classes of Pecten maximus were sampled. Suspension feeders dominate all megabenthic assemblages within the bay. This domination can be related to Crepidula fornicata spreading in the bay; however, no direct competition for food between scallops and the slipper limpet (introduced species) has been observed. On the other hand, Crepidula spreading leads to major changes in sediment type (silting) in the bay owing to biodeposit production, and silting would be a major factor inducing the decrease in Pecten maximus distribution. Predation would not be limiting. Within 10 years, one may predict a strong decrease in the area colonized by scallops in the bay.

Measuring feeding and absorption in suspension-feeding bivalves: an appraisal of the biodeposition method

In this paper we analyse methods that have been used to quantify the different physiological processes involved in food acquisition and absorption by suspension-feeding bivalves. In particular, we have considered those methods that have been used for determining food processing rates under ambient conditions of food availability. During the last few years, an increasing number of studies has been performed using the biodeposition method, which estimates feeding and absorption rates through measurements of suspended particles and biodeposit production. The main assumption of this method is that ingested particulate inorganic matter can be used as an inert tracer of feeding and digestive processes, i.e. that secretion or absorption of inorganic matter across the gut wall is negligible. There are several points that have to be taken into account when applying this method: a) the method assumes that sampled suspended particles and those retained by the gill are of similar organic content; b) faeces and pseudofaeces collection must be quantitative and separate and particle sedimentation must be controlled, if not avoided; c) where particulate food availability or composition is expected to fluctuate, the time lag for particles being captured and processed before they appear in the form of biodeposits must be evaluated to provide a proper reference value for available food. The biodeposition method and more conventional procedures provide equivalent results for estimating clearance rates. Moreover, predictions of scope for growth obtained with this technique also seem to be compatible with directly measured growth rates.

The influence of Atrina zelandica Gray on meiobenthic nematode diversity and community structure

The influence of the large suspension feeding horse mussel Atrina zelandica Gray on meiobenthic diversity and community structure has been studied at two sites in New Zealand where Atrina beds form discrete patches. Community attributes inside (IN samples) and outside the beds (OUT samples) in the bare sediment have been compared. At both a sheltered muddy harbour site and a more exposed coastal sandy site, significant effects were found. These were stronger, however, at the sheltered site: The presence of Atrina resulted in (i) a greater reduction in several univariate measures (including Shannon diversity), (ii) more pronounced changes in the form of k-dominance curves, (iii) greater differences in species composition as revealed by the R-statistic of ANOSIM, (iv) a higher value for average Bray Curtis dissimilarity between IN and OUT samples and, finally, (v) greater variability among the IN samples compared with the OUT samples as measured by the Index of Multivariate Dispersion. Variations in density of different nematode functional groups indicate that the detrimental effects of Atrina on meiobenthic biodiversity may be attributed to its activity (production of biodeposits) and physical presence, resulting in reduced oxygen concentrations in the sediment. At the exposed coastal sandy site, the mussels were older and probably produced less biodeposits per unit biomass, and also the wave-induced flows over the bed are more likely to result in sediment mixing, which will tend to blur local effects.

Filtration of the enteric bacteria Escherichia coli by two filter-feeding bivalves, Venus verrucosa and Mytilus galloprovincialis

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.

Biodeposit production by the mussel Mytilus edulis L. on rocky shores

Seasonal changes in the amount of biodeposit (faeces and pseudofaeces) produced by the mussel Mytilus edulis L., which is one of the representative suspension-feeders in the rocky intertidal and shallow subtidal regions of Mutsu Bay, were studied in the laboratory. The effects of water temperature, light, food concentration, flow rate, body size, age, and spawning on biodeposit production were investigated. More biodeposit was produced in summer than in other seasons. Throughout the year, the amount of biodeposit was positively correlated with body size. Relatively more biodeposit was produced by smaller than by larger individuals. A M. edulis population living in one square meter was estimated to produce 9.20 kg of faeces and 2.71 kg of pseudofaeces per year (dry wt). More biodeposit was produced at water temperatures of 17.6–20.2° C than at 4.5–7.6° C and 25.2–26.0° C. The optimum temperature for biodeposit production was found to be ≈ 20.0 °C. When kept in the dark, M. edulis produced more biodeposit than in the light. When food concentration is increased, more psuedofaeces are produced; the amount of faeces, however, remains constant. With increasing flow rate, the amount o f biodeposit per h increased but the biodeposition rate decreased. Larger amounts of faeces and smaller amounts of pseudofaeces were produced by younger mussels than by older ones of a similar size. Spawning also affected biodeposit production.