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The occurrence and abundance of the pelagic eggs of southern North Sea spring-spawning fish were analysed between 1984 and 2000. Species number varied between six (1986) and 14 (1999) and was positively correlated with sea surface temperature. With one exception, dab eggs were always the most abundant and usually highly dominant. Ranking of species depended on temperature, but no significant differences in ranking between years was discernible. Although with the increase in temperature in the 1990s a change in species assemblage was evident [species belonging to the boreal-Mediterranean (Lusitanian) group became more apparent in the species assemblage] this did not lead to an increased species diversity (Shannon Index) or a change in other community parameters. It appears that the recent developments regarding spawning stock biomass of commercial North Sea fish is reflected in the declining egg abundance of the respective commercial and larger species (i.e. cod, flounder, plaice) and an increase in abundance of the eggs of small species (i.e. long rough dab, rockling) over the years.

Eggs of dab (Limanda limanda) and plaice (Pleuronectes platessa) were experimentally exposed to ultraviolet-B (UV-B) radiation in a solar radiation simulator. The experimental design tried to simulate present and future conditions with reference to increased UV-B exposure due to northern hemisphere ozone loss, employing mainly two scenarios, a reduction to 270 (S1) and to 180 (S2) Dobson units (DU) in single or repetitive exposures of 2, 4 or 6 h. Depending on the total dose of UV-B irradiation and the developmental stage, exposed eggs displayed loss of buoyancy as a sublethal effect, as well as increased embryo mortality and reduced viable hatch. In the single exposure experiments only under conditions of 180 DU for 6 h were effects apparent. Double exposure under conditions of 270 DU did not lead to lasting effects. At the sublethal effect level, i.e. loss of buoyancy, considerable photorepair was observed. It was concluded, that under the present general weather conditions in spring and at the present levels of environmental ozone, allowing for a reduction to 180 DU, the embryonic development of North Sea spring spawning fish is not endangered by UV-B radiation.

Malformation rates in embryos of dab, whiting, cod, flounder, and plaice in the southern North Sea have been monitored between 1984 and 1995 by quantitative investigations of developmental defects in eggs immediately after capture. Incidences were highest in near-coastal waters known to receive high pollution loads. For all species and all areas investigated, synchronous trends were found with intermediate incidences in 1984, maxima in 1987 and significant decreases thereafter. The variations are compared with trends in organochlorine residues in dab and plaice from the German Bight collected over the same period. Trends vary for different organochlorine substances, but the overall picture indicates elevated levels in the period 1984-1987 and decreasing concentrations thereafter. Although the general pattern is consistent with the trend in incidences, significant correlations were only found for malformations of dab and concentrations of p,p′-DDE. Trends in concentrations of nutrients and hydrographic factors were also investigated, indicating a significant negative linear correlation between surface water temperature and incidence of malformed embryos of dab. The hypothesis is put forward that low temperature may predispose developing fish embryos to the impact of organochlorines.

In the spring of 1984 through and in the summer of 1987 pelagic flatfish eggs were collected in horizontal subsurface hauls with a 1-m ring net in the southern North Sea between 51°49' to 55°30'N and 2°30' to 8°00'E. The flatfish eggs were observed alive for their developmental stage and aberrations from normal development. Flatfish eggs occurring in the winter ichthyoplankton of the southern North Sea were dab, Limanda limanda ; flounder. Platichthys flesus ; plaice, Pleuronectes platessa , and long rough dab, Hippoglossoides platessoides . Summer samples contained dab, turbot, Psetta maxima ; little sole, Buglossidium luteum ; common sole, Solea solea ; Norwegian topknot, Phrynorhombus norwegicus , and lemon sole, Microstomus kitt . In winter as well as in summer eggs of dab were the most abundant in the southern North Sea with up to 249 eggs·m −3 surface water in winter and 26 eggs·m −3 in summer. The investigations revealed considerable quantities of abnormally developed flatfish embryos in the plankton samples. Highest malformation rates were recorded for the early stages of dab (44.4%) followed by flounder (41.3%) and plaice (26.0%) in winter; in summer these rates were for dab 18.9%, for turbot 14.1% and for little sole 12.5%. Generally malformation rates decreased with development. Areas of high malformation rates were off the river estuaries and in near-shore areas along the Dutch and German coasts. Malformation rates decreased with the distance from the coast. Causes and effects of the occurrence of malformations during embryonic development are discussed.

The trends of malformation prevalence in embryos of dab, Limanda limanda, in the southern North Sea after the year 1990 mirrored the drop in major pollutants in the rivers draining into the German Bight. Despite this general decline, we detected a pollution event in the southern North Sea in winter 1995/1996 employing the prevalence of malformations in pelagic dab embryos as an indicator. An abrupt rise in malformation prevalence in the embryos of dab, corresponded to a dramatic increase in DDT levels in parent fish from the same area, indicating a hitherto unnoticed introduction of considerable quantities of DDT into the system.

Malformations in fish embryos have been monitored for several years in the southern part of the North Sea. Their occurrence was thought to be related to pollution because malformation rates were highest in coastal waters, known to receive high pollution loads. For the embryos of all species synchronous trends for the fluctuation of the occurrence of malformations over time were registered in the areas covered, with intermediate prevalences at the beginning of the studies in 1984 and maxima in 1987. Thereafter, malformations in all species decreased significantly, followed by an abrupt increase in 1996. It was found that in addition to a close correlation between the concentrations of environmental pollutants in the water and in the fish a significant negative correlation existed between surface water temperature and the occurrence of malformed embryos of dab (Limanda limando). These same correlations were also observed for other fish species over time and space. This temperature-related correlation became increasingly visible with decreasing concentrations of organochlorines in fish. From these findings it is concluded that aside from environmental pollutants, natural factors such as temperature may predispose developing fish embryos to the impact of pollutants.

1. For water pollution control purposes, the concentration-addition model for describing the joint effects of mixtures of toxicants on aquatic organisms is appropriate; in this model the contribution of each component in the mixture is expressed as a proportion of the aqueous concentration producing a given response in a given time (e.g. p 96-h LC50). 2. Examination of available data using this model shows that for mixtures of toxicants found in sewage and industrial effluents, the joint acutely-lethal toxicity to fish and other aquatic organisms is close to that predicted, assuming simple addition of the proportional contribution from each toxicant. The observed median value for the joint effect of these toxicants on fish is 0.95 of that predicted, and the corresponding collective value for sewage effluents, river waters, and a few industrial wastes, based on the toxicity of their constituents, is 0.85, while that for pesticides is 1.3. 3. The less-than-predicted effect of commonly-occurring tox...

Seasonal fluctuations of the meat content of blue mussels were recorded together with their parasitation. From these data the correlation between numbers of Mytilicola intestinalis and the meat content of the respective mussel was analysed statistically. Meat content of mussels was lowest when spawning occurred (May). Fluctuations of meat content of parasitized and non-parasitized mussels did not reveal any marked differences. Statistical analysis of the relationship between number of parasites and meat content of mussels gave no proof of significant correlation.

Artificially inseminated eggs of feral North Sea whiting (Merlangius merlangus) were incubated in the laboratory in order to determine reproductive success. After incubation, two measures for reproductive success, total hatch and viable hatch, were determined and correlated with chlorinated hydrocarbon residues in the respective ovaries. From their specific toxicities and the sum of all determined chlorinated hydrocarbon contaminants, a contamination factor (CF) was calculated. Significant negative correlations were found between total hatch and DDT, including its metabolites (ΣDDT), dieldrin and the CF. ΣDDT and the CF were also negatively correlated with viable hatch. A threshold value of ovary contamination above which impairment of reproductive success was likely to occur was set at > 200 μg kg−1 wet wt. for ΣPCB, > 20 μg kg−1 wet wt. for ΣDDT and > 10 μg kg−1 wet wt. for dieldrin.

Juvenile flounder and common mussel from the Baltic Sea were kept in Corexit 7664 (50 µg/l) and cadmium (5 µg/l)-contaminated, recirculated, sea-water systems for 200 days at 15 °C and 20 ‰ S. Accumulation of cadmium with exposure time was measured in several fish tissues and in mussel. There were no differences in the cadmium accumulation by tissues with or without the addition of Corexit 7664. No acute effects of the contaminants on the experimental animals could be noted. Final cadmium concentrations, reached for all biological matter analysed, were 4 times higher than in full-strength sea water.

In February/March 1983 and 1984 a survey of pelagic fish eggs was conducted in the western Baltic (Kiel Bight), employing a horizontally towed plankton net (1 m O and 300 μm mesh). Maximum egg numbers in the upper meter of the S=21×10−3 salinity layer were 200·100 m−3. The most abundant eggs were cod (up to 142 eggs·100 m−3), followed by plaice (up to 74 eggs·100 m−3) and flounder (20 eggs·100 m−3). A considerable percentage of embryos of all species displayed aberrant development. In 1983 18% of cod, 22% of flounder and 24% of plaice eggs caught contained defective embryos; in 1984 this number was larger, ranging from 28% in plaice over 32% in cod to 44% in flounder. Early developmental stages showed the highest malformation rates (up to 51% in the case of early flounder embryos). With progressive development, malformations decreased in numbers, being lowest prior to hatching. Highest rates of malformations were recorded in the Mecklenburg Bight in 1983. A second area with high incidence of malformation rates was located south and east of the island of Langeland. Several reasons, including environmental and anthropogenic factors, for the occurrence of malformed embryos in pelagic fish eggs are discussed. The potential of malformation rates in embryos of pelagic fish eggs as a tool for monitoring is considered.

1. Eggs of herring(Clupea harengus), flounder(Platichthys flesus), and garpike(Belone belone) were incubated in cadmium contaminated water (0.05–5.0 ppm) and newly hatched larvae analyzed for cadmium contents. 2. Cadmium residues in newly hatched larvae were dependent on cadmium concentrations employed during incubation. 3. Cadmium contents of newly hatched flounder and herring larvae (0.7–2.3 ng Cd/0.1 mg dry weight) were of two orders of magnitude higher than inBelone belone larvae incubated under the same conditions (0.0017–0.0185 ng Cd/0.1 mg dry weight). 4. Cadmium contents of herring and flounder larvae held in cadmium contaminated water increased with exposure time. 5. Cadmium contents of herring larvae exposed to cadmium contaminated water for 8 days were of one order of magnitude higher than contamination of flounder larvae kept under similar conditions (max. value for herring 48 ng Cd/0.1 mg dry weight; max value for flounder 5.4 ng Cd/0.1 mg dry weight). 6. Cadmium contents ofBelone belone larvae and juveniles kept at 0.05 ppm Cd for 30 days were significantly higher than cadmium contamination of control specimens.

Two recirculated marine seawater systems (capacities: 150 and 300 l) were used for the study on cadmium accumulation of biological filter sludge, by the musselMytilus edulis and the plaicePleuronectes platessa for a period of up to 300 days. In the contaminated system Cd concentrations varied from 2.5 to 7.0 μg/l with a mean of 4.6±1.15 μg/l (control: 1.04±0.46 μg/l). Accumulation of Cd by the filter sludge from the control system as well as from the contaminated system was significant. Mean concentrations of control-and contaminated sludge over the experimental period were 2.01±0.86 ng Cd/mg dry wt and 9.98±3.55 ng Cd/mg dry wt respectively. Accumulation of Cd byM. edulis both in the control and in the contaminated system was considerable. After 163 days of exposure the whole body burden of mussels rose from 0.3 ng Cd/mg dry wt to around 10 ng Cd/mg dry wt in the controls and to 70 ng Cd/mg dry wt in the contaminated systems. Accumulation of Cd byP. platessa was analysed in backbone, fins, gills, liver, muscle (fillet), otolith and skin (dorsal and ventral) over a period of 280 days. Elevated Cd contents of livers from control specimens were noticed after 200 days and reached 1.75 ng Cd/mg dry wt in liver. There was considerable accumulation in the liver (maximum values: 3.0 ng Cd/mg dry wt) and gills (6.0 ng Cd/mg dry wt) of specimens from the contaminated system, Cd contents of plaice exposed for identical periods of time were very variable. Growth of plaice living in the contaminated system was at times significantly slower than that of the control group. Of the three biological objects tested-filter sludge,M. edulis, P. platessa—the mussel seemed to be the most sensitive indicator of elevated Cd-concentrations, while the reaction of the plaice was slow and less distinct.

Prior to the studies reviewed here, only lymphocystis and skeletal deformities of a variety of fish species and certain diseases of eel were known to occur in the German Bight (North Sea). From 1977 until now, 9 externally visible lesions on North Sea fishes were observed; in addition to those mentioned before, they comprise: fin rot, ulcerations, epidermal papilloma, hyperplasia, pseudobranchial tumour, eye diseases and gill swellings. With the exception of information on changes in frequencies of vertebral deformities of herring from the 1950's to the 1970's, there are no long-term data characterizing changes in frequencies of the diseases under study. For pseudobranchial tumours of cod and epidermal papilloma of dab, information is provided on occurrence and abundance. The distribution pattern of cod afflicted with pseudobranchial tumours is strongly influenced by the migratory behaviour of the fish. Epidermal papillomas of dab were more frequently found at stations within the inner German Bight than in neighbouring areas. The Bight is used for dumping of wastes from titaniumdioxide production. Further disease hot spots are areas off the Humber estuary and the British coast. Analysis of chromium in dab from the German Bight revealed elevated concentrations in epidermal tissues of specimens from the dumping area compared with that found in dab from neighbouring localities. Particulate iron was demonstrated to occur in mucous cells of dab from the dumping area. From increased levels of heavy metals with cancerogenic potential in sensitive target tissues and from increased prevalences of diseased fish in the dumping area it is concluded that these phenomena are possibly causally linked. In the vicinity of the Humber estuary high disease rates were encountered and areas with high prevalences of dab afflicted with epidermal papilloma extended over regions shown to be transport routes for persistent pollutants such as radioactive materials. It is therefore suggested that the long-range distribution of fish diseases in the southern North Sea might reflect the long-range transport of persistent pollutants.

Although cadmium concentrations of unpolluted sea water are low, ranging from 0.01 to 0.41 µg/1 (Goldberg, 1965; Preston, 1973; Chester & Stoner, 1974; Kremling & Petersen, 1977) concentrations in estuaries are from 10 to 100 times higher, as reported by Butterworth, Lester & Nickless (1972) for the Severn and Eustace (1974) for the Derwent estuaries. Unusually high cadmium concentrations of 50 µg/1 have been found by Chan, Cheung & Li (1974) in Hong Kong harbour water. The cadmium in the drinking water (225 µ/l) and the food (rice) of Japanese farmers is believed to have caused the ‘itai-itai’ disease (Kobayashi, 1971), a pathological syndrome characterized by kidney damage with bone disease.

Like most heavy metals, cadmium is only found in minute amounts in natural sea water. Krauskopf (1956) stated that cadmium concentration of normal sea water ranges from 0.032 to 0.075 PPb (μg/l−1) while Goldberg (1965) gave a somewhat higher value of 0.11 ppb. Cadmium concentrations determined by Preston (1973) for the North-East Atlantic Ocean range from

Due to their formerly wide-spread use and their slow degradability chlorinated hydrocarbons today are ubiquitous in the environment and tend to accumulate in marine biota. Many of these substances, being highly toxic (pesticides), have long since been suspected of exerting detrimental effects on metabolism and reproductive capacity of highly contaminated individuals. In the present contribution it could be shown that levels of PCBs found in ovaries of three marine teleosts correlate with a loss of reproductive capacity in afflicted specimens. Male gonads did contain lower concentrations of chlorinated hydrocarbons than did ovaries; the variability in hatching success therefore seems to depend on the contamination of ovaries. Effective PCB ovary burdens were in the range of 120–180 ng/g tissue wet weight. Pesticides such as DDE and Dieldrin seem to impair reproductive success too, measured as the emergence of viable larvae from eggs of contaminated parent fish.

Investigations during several cruises (1979–1981) showed that Atlantic cod with pseudobranchial tumours occurred in all areas investigated. Statistical analysis of data revealed that there was a marked prevalence of the condition in the centre of the German Bight, whereas a lower incidence of the condition was observed on the Dogger Bank, off the Dutch coast and in the western Baltic Sea. The higher prevalence of pseudobranchial tumours in the German Bight coincides with a dense population of cod and impacts of pollution.

Running ripe Baltic flounder Piatichthys flesus were caught with a bottom trawli. Eggs were stripped and artificially inseminated and incubated in Baltic sea water at 6.8 °C and a salinity of 27.5% After hatching, siraight and viable appearing larvae — viable hatch — were determined. Ovary and liver samples of the female parental fish were collected and analyzed for chlorinated hydrocarbons and heavy metals. Viable hatch was significantly affected at ovary chlorinated hiphenyl (PCB) levels higher than 120 ng/g wet weight. Thus 120 ng/g PCB was designated a threshold level in flounder eggs. above which reduced survival of developing eggs and larvas can be expected. Other chlorinated hydrocaihons. and metals did not show any correlation between ovary and/or liver contamination levels and viable hatch. The melhod employed is deemed to be a promising tool for the assessment of pollution effects on marine biola.

Eggs of Baltic herring were incubated (10°C; 16‰S) in sea water containing mixtures of Cd, Cu and Pb at concentrations of 0.56–5.0, 0.0167–0.15, 0.56–5.0 mg metal/l; embryonic survival until hatching, viable hatch and uptake of metals by embryos and early larvae were measured. Negative effects of metals on embryonic survival and viable hatch were additive in the case of Cu and Cd. Pb did not exer detrimental effects. Uptake of metals with exposure time was non-linear in eggs and linear in larvae. Total uptake of Cu and Cd by eggs was subjected to antagonistic or synergistic action of the other two metals present. Accumulation of Pb by eggs was enhanced when Cu was also present.

Red mud is an industrial waste originating from the production of aluminium from bauxite. Since the difficulties connected with the removal of red mud are increasing and the possibilities for land deposition are restricted, German aluminium-producers wanted to dump their wastes in the southern North Sea. Several experiments were carried out to assess the effects on marine organisms. Red mud proved to be harmful to a variety of organisms; the most predominant effect was agglutination of gill tissues. Regarding the very severe effects of suspended red mud on different marine organisms the authors refuse the proposed dumping project. Taking into account the special hydrographic situation of the German Bight, which cnanot be compared with that of other dumping areas and further knowing that the North Sea is one of the most important fishery areas of the world, it is concluded that dumping of red mud would endanger the stocks of bottom fish and fauna and should therefore take place in regions without any fishing activities with depth greater than 3000 m.

From 1961 to 1980 annually 350 000 m 3 of sewage sludge of the City of Hamburg were dumped into an area located in the outer stretches of the Weser and Elbe estuary in the inner German Bight of the Southern North Sea.