L. De Wolf

Spatial and seasonal differences in the PCB content of the mussel Mytilus edulis

Seasonal and spatial variation in the concentration of PCBs, fats (non-polar lipids) and total lipids and the condition of the mussel Mytilus edulis were assessed in three differing water bodies of the Dutch delta area. Highest concentrations of PCBs in the mussel were found in the Westerschelde estuary, with much lower concentrations in the Oosterschelde and the brackish lake Grevelingenmeer. Spatial differences were strongly related to salinity; lower concentrations were found at the more saline stations, pointing to freshwater inputs as being the origin of the PCBs in mussels. The PCB concentration in mussels, on the basis of dry or total weight, in general increased during summer, autumn and winter and decreased strongly during spring. The strong decrease is related to the spawning of gametes. Seasonal changes in the PCB concentration on the basis of the dry weight were not related to changes in the fat content or the condition of the animals. Only PCBs on a fat basis were negatively related to fat content, indicating a dilution of PCBs during seasonal fat accumulation and concentration of PCBs during fat utilization, in such a way that the total PCB concentration in the animal remains the same. It seems that, besides reproduction, equilibrium partitioning is the most probable mechanism that determines the PCB content of mussels.

Relationship between PCB concentrations and reproduction in mussels Mytilus edulis

Abstract Changes in the concentrations of PCBs and fats were followed in mussels Mytilus edulis, transferred vice versa between a polluted estuary (Westerschelde) and a relatively low-pollution sea-arm (Oosterschelde). The concentrations in the mantle, which contains the gonads, were determined separately from the rest of the body. The fat content of the mantle increased 1 1 2 - to 2-fold during the observation period (autumn, winter) and remained constant in the rest of the body. Polychlorinated biphenyls (PCBs) in mussels transferred from the polluted to the less polluted area were not eliminated. In the mussels transferred to the polluted area the increase of the PCB content was 2- to 3-fold over a period of 3 months. PCBs in the mantle, and therefore in the gonads, can amount to more than 40% of the total PCB load in a mussel. It was concluded that during the spawning of gametes a substantial proportion of the PCBs may be shed.

Sensitivity to stress in the bivalve Macoma balthica from the most northern (Arctic) to the most southern (French) populations: low sensitivity in Arctic populations because of genetic adaptations?

The stress sensitivity, determined in copper exposure experiments and in survival in air tests, and the genetic structure, measured by means of isoenzyme electrophoresis, were assessed in populations of the Baltic clam Macoma balthica (L.) from its southern to its northern distribution limit, in order to test the hypotheses that near the distribution limit the clams would be more stress sensitive and would have a lower genetic variability. The populations in west and north Europe show a strong genetic resemblance. The populations in the sub-Arctic White Sea are genetically slightly different, and show a low stress sensitivity. The populations in the Arctic Pechora Sea are genetically very distant from the other populations, and show the lowest stress sensitivity. Near the southern distribution limit, in agreement with the hypotheses, genetic variability is low and stress sensitivity high. On the other hand, in contrast to expectation, near the northern distribution limit, in the populations of the Pechora Sea, the genetic variability was higher, thus not reduced, and the stress sensitivity was low compared to all other populations. Yet, it remains a question if such is due to gradual physiological acclimatization (and ongoing differential selection) or to genetic adaptation.

Decomposition of Spartina anglica, Elytrigia pungens and Halimione portulacoides in a Dutch salt marsh in association with faunal and habitat influences

Decomposition of Spartina anglica, Elytrigia pungens and Halimione portulacoides was studied for 20.5 months in situ in two habitats on a salt marsh in The SW Netherlands. Litter bags of three different mesh sizes were used to exclude meio- and/or macrofauna. The middle-marsh habitat was flooded more frequently than the plant-debris habitat in the highest marsh zone. Decomposition of the three species followed an exponential pattern of decay: instantaneous decay rates varied from 0.0026 to 0.0054 per day. Decay rates were significantly influenced by habitat factors and fauna, while there was a significant interaction between plant species and habitat. In case of a significant meio- and/or macrofauna effect, this became noticeable 12–16 weeks after the start of decomposition and resulted in a difference of 5–10% ash-free dry weight remaining after 20.5 months. Nematodes were the dominant microfaunal group in the plant litter. Densities were influenced by habitat conditions but not by resource quality, season and meio- and/or macrofauna. Only initial C/N and C/P ratios were correlated with differences in decomposition rates between the plant species. During the later stages of decomposition N and P concentrations of the plant litter were higher in the plant-debris habitat than in the middle-marsh habitat, probably as a result of fluctuating detritivores densities. The course of the decomposition process differed per plant species and per habitat. The results of this study underline the importance of knowledge of long-term decomposition rates.

The annual cycle of glycogen in estuarine benthic animals

Glycogen is an important reserve constituent in invertebrate animals, especially in bivalves (BAYNE and NEWELL, 1983; GABBOTT, 1983; GADE, 1983; AKBERALI and TRUEMAN, 1985). It may be used to overcome long periods of food shortage, as in winter, or to mitigate shortterm periods of stress like periods of anoxia or prolonged emersion. Moreover glycogen can be reallocated during gametogenesis from the soma into (glycogen and lipid) reserves in follicles and gametes. Consequently, minimal values in the glycogen content may be expected at the end of a winter or reproduction period. Most information on annual cycles of glycogen in marine benthic animals is available for commercially important species, e.g. Mytilus eduli

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

(ZANDEE etal., 1980; DE ZWAAN and ZANDEE, 1972a), Ostrea eduli

The development of a benthic ecosystem

(RUSSELL, 1923; GAARDER and ALVSAKER, 1941; KRVARIC, 1953; WALNE, 1970) and Arenicola marina (DE VOOYS, 1975). From studies on the effects of prolonged emersion on estuarine benthic animals (HUMMEL etal., 1986a, b) additional information is available on the annual cycle of glycogen in some noncommercial animals. In the present study new data on annual changes in glycogen content of both commercial and non-commercial benthic species are presented. The changes are related to season and reproduction period. Animals were sampled in the Southwest Netherlands, from intertidal areas in the Oosterschelde, mostly near Yerseke, with the exception of Ostrea edulis which was sampled subtidally in the brackish Lake Grevelingen. After sampling the animals were stored at 20 ~ before analysis. For the glycogen analysis 5 to 10 animals were pooled. The measurements were performedaccording to the method of VAN HANDEL (1965), modified by DE ZWAAN and ZANDEE (1972b). Glycogen content was expressed as a percentage of the dry flesh weight obtained after drying at 80 ~ for 3 days. Spawning periods, which indicate the end of the reproduction period, were taken from the literature: for Myt~lusedulis L. from BAYNE (1976) and SASTRY (1979), for Cerastodermaedule (L.)from CREEK (1960), BOYDEN (1971), KINGSTON (1974), SEED and BROWN (1977) and NEWELL and BAYNE (1980), for Ostrea edulis L. from KORRINGA (1941) and Wl LSON and SIMONS (1985), for Littorina lit-torea (L.) from ANKEL (1938), FRETTER and GRAHAM (1962) and WOLFF (1973), for Arenicola marina (L.) from WOLFF (1973), DE VOOYS (1975), DE WILDE and BERGHUIS (1970) and MAYES and HOWIE (1985), for Nepthyshomberg/i Savigny from WOLFF (1973) and OLIVE eta/. (1985), and for Sagartia troglodytes (Price) from PAX (1936), RIEMANN-ZURNECK (1969) and CAMPBELL (1974). For Diadumene cincta Stephenson no data are available. Most species showed considerable seasonal changes in the glycogen content; high values were found in summer and autumn, low values in winter and spring (Fig. 1). The glycogen content in the bivalves reached the highest values, up to 30 % of the dry weight, and showed the strongest fluctuations. The glycogen content of all other species remained below 10 %. Similar values and fluctuations were found before for Mytilus edu/is (ZWAAN and

Mortality of intertidal benthic animals after a period of prolonged emersion

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]

Growth in the bivalve Macoma balthica from its northern to its southern distribution limit: a discontinuity in North Europe because of genetic adaptations in Arctic populations?

The development of a benthic ecosystem on a sandy bottom at 3 m depth in the saline Lake Grevelingen, The Netherlands, is described. The development started after the closure of the former Grevelingen estuary and was followed for 4 1/2 years. Ecosystem attributes studied were biomass, secondary production, production/biomass ratio, type of food chains, species diversity, pattern diversity, size of organisms, type of life-cycles, and r- and K-selection. The results are discussed in relation to E. P. Odums (1969) theory of ecosystem development.

The effects of extended periods of drainage and submersion on condition and mortality of benthic animals

Abstract Tidal manipulation by means of a storm-surge barrier in the Oosterschelde basin, The Netherlands, may cause prolonged periods of emersion. The effects of such extended emersion on the mortality of benthic animals living on tidal flats were assessed. Mortality rates were minimal between 0 and 5°C. Greater mortality rates were found at higher as well as lower temperatures. Mortality also increased with longer periods of emersion. The species could be allotted to five groups, ranging from the first group which showed hardly any mortality at any temperature to the fifth group which had a mortality rate of 5–10% · day −1 at ≈ 5°C and of 50% at ≈ 20°C. At the community level, calculated as a weighted average of the five species groups, 50% mortality was not reached within 11 days between − 1 and 4 °C. Below − 1 and > 19°C, however, 50% mortality occurred within 3 days. Interspecific differences in the relation between mortality, period of emersion and temperature coincided with taxonomic and morphological differences. Bigger species and those with shells (gastropods, bivalves, bigger polychaetes) are more resistant to emersion than smaller species and those without shells (small polychaetes, anemones).