Hervé Rybarczyk

Uniform variation in genetic traits of a marine bivalve related to starvation, pollution and geographic clines

Consistent patterns of genetic variation in the marine bivalve Macoma balthica (L.) were found after exposure to low levels of copper, starvation, and along geographic clines. The geographic clines were related to temperature and salinity. Genetic differences were primarily found in the LAP (Leucine aminopeptidase) locus; under stress the frequency of one specific allele, and thereby the heterozygosity, decreased strongly. The degree of changes depended on age and condition of the animals; adult animals showing stronger changes than juveniles. Low concentrations of copper yielded stronger genetic changes than high concentrations. It is concluded that genetic diversity and stress-sensitivity of species change predictably along a gradient in response to environmental harshness. Animals near the southern limit of their range were more sensitive to additional stress.

A comparative study on the relation between copper and condition in marine bivalves and the relation with copper in the sediment

The relation between condition and copper concentration was assessed in three bivalve species (the Baltic clam Macoma balthica, the cockle Cerastoderma edule and the mussel Mytilus edulis) from several Dutch and French estuaries. In general, the copper concentration in the bivalves was negatively related to condition. The slope of this relation was strongest in the Baltic clam M. balthica, with an almost inversely proportional change of Cu concentration at a change of condition, indicating an almost constant Cu content (body burden) per individual, i.e. no elimination or accumulation of Cu. In the mussel M. edulis, the slope of this relation was absent or the weakest, with an almost uniform Cu concentration at a change of condition, indicating an almost proportional elimination (or accumulation) of Cu at a decrease (or increase) of the condition. Thus in Baltic clams the copper body burden is kept at an almost constant level, whereas in mussels the copper concentration is almost constant. In Baltic clams, but not in mussels and cockles, spatial differences were related to copper concentrations in the sediment. It is discussed that mussels maintain a homeostatic Cu concentration within a short time-period (days; copper highly exchangeable by complexation to metallothioneins), whereas the Cu concentration in Baltic clams is more slowly regulated (several weeks; fossilization of copper in mineral granules) and remains on an average in (partitioning) equilibrium with the Cu concentration in the sediment. Therefore, the Baltic clam is a better indicator of sediment copper pollution than the commonly used mussel. In addition, the observed differences between species were compared with differences in their life-strategies. The Cu concentration in the sediment is strongly related to the silt fraction (< 16 μm) of the sediment.

Sensitivity to stress of the estuarine bivalve Macoma balthica from areas between the Netherlands and its southern limits (Gironde)

Abstract Variation in the sensitivity to stress of Macoma balthica was measured in several French and Dutch estuaries. For adult and juvenile Macoma balthica exposed to copper under conditions of starvation, differences in mortality rate, condition, glycogen, burrowing rate and copper content were assessed. No significant differences were observed between adults and juveniles; the influence of treatment and origin was always evident. Animals from the most southern estuaries, Loire and Gironde, near to the speciess southern limit of distribution, showed, in the field, the strongest deviations for the ecophysiological traits measured, and were in the experiments the most sensitive to stress.

Free amino acids as a biochemical indicator of stress in the estuarine bivalve Macoma balthica

The use of free amino acids (FAA) as a stress indicator was assessed during a copper exposure experiment for specimens of the estuarine bivalve M. balthica from a geographical gradient extending from the Netherlands to its most southern limit of distribution in the Gironde, France. Changes in FAA were significant. A higher alanine content at the start of the experiment coincided with a lower mortality-rate during copper exposure. During copper exposure the tissue concentrations of alanine increased. It is concluded that especially the concentrations of alanine, and to a lesser degree the taurine/glycine (T/G) ratio, can be used as stress-indicators for M. balthica. Animals near the southern limit of their distribution showed the strongest deviations from average values. The age of the animals (2-7 years) had no influence on results. [KEYWORDS: free amino acids; Macoma balthica; stress; copper;bio-indicator; geographic dine Mytilus-edulis-l; pollution; proteins; cadmium]

Échanges de sels nutritifs entre la zone côtière et un système estuarien intertidal : la baie de Somme (Manche, France)

Abstract Nutrient exchanges between coastal water and an intertidal estuary: the Bay of Somme (English Channel, France). The Bay of Somme is the second ranked estuarine system, after the Seine estuary, on the French coasts of the Eastern Channel. The nutrient retention and regeneration capacities of this estuary have been calculated from continental and coastal hydrological data and from estimation of the residence time. Measurements at the mouths of the main rivers over a one-year period (from October 1994 to November 1995) were used to construct a budget of continental inputs which showed that the smaller rivers could, at times, be important contributors. The annual budget shows continental inputs of nitrogen, phosphorus, silicon and suspended particulate matter of 9 000 t · y−1, 380 t · y−1, 5 400 t · y−1 and 67 800 t · y−1. Estimation of coastal inputs to the system shows two fluxes of different origins: a flux of nitrogen, mainly nitrate, from the Somme river and a flux of phosphate from the southern coastal area. The interaction of these two inputs may explain the high biological activity of this system. A high degree of retention of nitrogen was calculated and is attributed to uptake by phytoplankton which is itself exported as organic particulate matter. A new estimate of primary production is put forward which distinguishes between new production, regenerated production and microphytobenthic production. The estimated total primary production (600 gC·m−2·y−l) is comparable with that of the Wadden Sea (The Netherlands). The model thus developed for studying exchanges is a useful tool for studying system function and provides a more accurate estimate of the role of continental inputs from the Bay of Somme in the context of coastal water nutrient enrichment in the Eastern Channel and southern Bight of the North Sea.