Endocrine disrupting chemicals (EDCs) are one of the many anthropogenic pollutants released into the environment. There is a substantial body of literature that has shown a detrimental impact on wildlife, particularly aquatic species, following exposure to these pollutants. In particular, exposure to EDCs can cause disruptions in sexual development and reproductive function. The majority of the effects observed are alterations in the physiology and behaviour of individuals and a key research question that has yet to be fully addressed is whether the effects seen in individuals exposed to EDCs manifest in measurable changes in population parameters. Whilst some work has been conducted previously investigating the population-level impacts of EDC exposure, this work has generally used mathematical models to examine whether measured short-term changes in individual fecundity and survival may lead to alterations in population viability and growth in the long-term. Such an approach ignores the potential impact of EDCs on more subtle factors (for example alterations in behaviour and genetics) that can potentially affect fish population dynamics. The work presented in this thesis used two model species, the zebrafish, Danio rerio and stickleback, Gasterosteus aculeatus, to examine whether exposure to EDCs had an effect on previously ignored factors that determine group dynamics, including behaviour, parentage and reproductive success. In groups of zebrafish (two males and two females) exposure to the model oestrogenic compound ethinylestradiol (EE2) at 10 ng/L caused a reduction in the paternity success of the most successful male, reducing the skew in paternity, relative to controls. This disruption in the reproductive hierarchy was associated with a suppression of 11-ketotestosterone (11-KT) concentrations in exposed males. Such alterations in reproductive hierarchies have implications for population genetic diversity as well as usual patterns of sexual behaviour and selection. In a second study, males were exposed to EE2 (females were not exposed) and then placed into colonies of varying size with either 1, 2 or 4 males competing to breed with one female. The reproductive success of the most reproductively successful male in colonies containing two males and one female was unaffected by previous exposure to EE2, relative to controls, but was significantly affected for the most reproductively successful male in tanks containing four males competing to breed with one female. This finding suggests that the impact of EDC exposure on reproductive hierarchies and success is dependent on the group structure and is not a straightforward monotonic effect. It is well known that there exist so-called ‘windows of sensitivity’ for the effects of EDCs on sexual development in fish. Exposure to EDCs during this period can cause dramatic alterations in development, including complete sex reversal if the magnitude and/or duration of exposure are sufficient. In the third study in this thesis, zebrafish were exposed during the key window of sexual development, from 20-60 days post fertilisation (dpf). The reproductive success of both mature males and females was then examined in competitive breeding scenarios. Whilst there were no obvious effects of the early life EE2 exposures on the gonadal phenotypes in either males or females at maturity, the reproductive success in males exposed to 2.76ng EE2/L was increased. In contrast, exposure of females to 9.86 ng EE2 /L during early life reduced their subsequent reproductive success. Given the importance of female reproductive capability in population demographics and dynamics, the effect of exposure to EE2 on female reproductive success may therefore have significant implications for exposed fish populations. Whilst conducting the EE2 exposure experiments, it became clear that the genetic diversity in the laboratory strains of zebrafish was much lower than that previously published for wild zebrafish. A study was therefore conducted in which several laboratory strains of zebrafish and a population of zebrafish obtained directly from the wild in Bangladesh were genotyped in order to elucidate the genetic diversity in the different strains. The results showed that the genetic diversity in commonly used laboratory strains (even those described as outbred or ‘wild type’) was significantly lower than that of wild zebrafish. Given the impact of reductions in genetic diversity and variation on fitness at both the individual and population level, this has implications for studies that extrapolate results from laboratory studies to wild populations, as exposure to EDCs may have a different impact on laboratory strains than their more genetically diverse wild counterparts. The final study conducted examined populations of wild sticklebacks (Gasterosteus aculeatus) from either clean sites or sites with a history of exposure to anthropogenic pollutants, particularly EDCs from sewage effluent. All the populations examined from sites with a history of pollutant exposure showed evidence of population bottlenecks, whereas populations from clean sites did not. Fish from the different populations were then placed into competitive breeding mesocosms. Each mesocosm contained an equal number of males from a clean, control reference site and from one of the polluted sites. The same number of females from a clean, control reference site was also added to the mesocosm. Males from all polluted sites were able to compete and breed successfully when placed in these competitive breeding scenarios and there was no evidence that they had reduced reproductive success. The implication of this finding is that even if exposure to anthropogenic EDCs has impacted on the genetics of a wild population, the reproductive potential of individuals may not necessarily be altered.

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Bioindicator organisms and assemblages were used to monitor the levels and effects of pollution, and assess the conservation value of sites in Swansea Bay and the adjacent Gower Peninsula. Swansea Bay has a long history of effluent input to the marine environment from domestic and industrial sources. A major short sea outfall located at Mumbles Head (west of Swansea Bay) discharged partially treated sewage effluent near to adjacent limestone shores from the 1930s to February 1999. Closure of this outfall provided a good opportunity to study the effects of sewage pollution on shore ecology. Rocky shore community structure was monitored monthly from January 1998 to June 2000, and kelp holdfast community structure was monitored seasonally from winter 1997/1998 to spring 2000 (excluding summer periods) at both Mumbles Head and Oxwich point, on the relatively unpolluted south Gower coast. Significant spatial and temporal variability in community structure was identified, potentially attributable to pollution, as well as natural abiotic and biotic factors such as high turbidity levels, episodic storm events, mass settlement and invasions of keystone species, each within the potential to mask any pollution effects. Significant spatial and temporal variability was also identified in the Body Condition Index (BCI) calculated for <I>Mytilus edulis</I> collected monthly from November 1997 to July 2000 at Mumbles Head and Oxwich Point. The mean BCI was higher at Mumbles Head than at Oxwich Point. This could be a result of differences in food supply resulting form riverine, domestic and industrial discharges. Closure of the sewage outfall at Mumbles Head did not have a discernable effect on the mean BCI. <I>Fucus serratus</I> and <I>Mytilus edulis</I> were used as bioindicators of heavy metal contamination at sites in Swansea Bay and on the Gower Peninsula. Higher concentrations were recorded at sites in Swansea Bay as opposed to those located on the Gower Peninsula. Heavy metal concentrations reported in this study at Swansea Bay were generally lower than values reported in the 1970s and 1980s (with the exception of Cu and Zn in <I>Fucus serratus</I>), reflecting reductions in metal discharges from the rehabilitated River Tawe catchment. Closure of the sewage outfall at Mumbles Head did not have a discernable effect on metal concentrations in <I>Fucus serratus</I> or <I>Mytilus edulis</I> at any of the sites investigated.

The effects of a range of pollutants on a number of moss species were investigated by field and laboratory experimentation. Effects were demonstrated on growth, reproduction, development, survival, morphology, anatomy and physiology, in particular, pigment and membrane systems. Although a range of response exists within species, which varies with pollutant used, concentration applied, and exposure time, species can be classified into two groups: resistant species which can withstand higher levels and longer exposures to pollutants than the sensitive species which are killed at lower concentrations. This grouping is maintained over gaseous, metallic and fluorine pollution treatments. An investigation of effects on reproduction and development, showed that species fall into the same two groups throughout both sexual and asexual life cycles. Species belonging to the two groups also have initially different patterns and potentials for development, resistant species possessing features which would be advantageous in polluted environments e.g. growth rate and development cycle are fast. Since species vary in their survival ability, they must differ physiologically, Studies of uptake of heavy metals by species from the two groups were made to investigate the site and mechanism of tolerance. Simultaneous measurements of pollutant uptake and moss health showed that resistant species accumulate more pollutant and are damaged at higher internal concentrations of pollutant than sensitive species. This enabled a hypothesis to be set up that the cell wall is the site of the tolerance mechanism. By acting as a "mop" with a finite capacity for absorbing metal ions, especially in resistant species, the wall could keep pollutants away from the metabolic sites, which were found to be equally sensitive in both groups. Once these sites become saturated, damage to membranes and subsequently pigments, occurs . The species demonstrated to be resistant experimentally are the ones commonly in polluted environments, where as sensitive species are not normally found in polluted environments.

Oil production in the North Sea sector pre-1990 used predominantly oil-based drilling muds. The drill cuttings still contained significant amounts of muds and associated hydrocarbons despite cleaning prior to disposal onto the seabed. The cuttings accumulating on the seabed caused physical smothering and toxic effects of the hydrocarbons or other constituents of the muds. Although decreases in hydrocarbon levels have been observed over 10 years, it has been difficult to distinguish whether this 'decrease' is due to natural attenuation or whether it is an artefact of the sampling methods. This study aimed to answer this question by determining whether the biological potential for hydrocarbon-degradation was in place by using integrated molecular, microbiological and analytical chemical and biochemical techniques. Several bacterial isolates were retrieved from drill cuttings material. The aerobic isolates belonged to the genus Halomonas or were closely related to the genera Marinomonas or Pseudoalteromonas and were capable of degradation of the main constituents of oil-based drilling muds. The anaerobic isolates were sulphate-reducing Desulfovibrio species for which indications of hydrocarbon-degrading capacity were found. The isolates were shown to be active in cuttings pore water as well as at the in situ temperature. ATP measurements and molecular techniques (DGGE/PLFA) indicated the presence of a highly active community with a population structure different to the surrounding clean sediment and suggested strong presence of metal- and sulphate-reducing bacteria. Anaerobic microcosm experiments with 14C-labelled hydrocarbons were used to determine the extent of degradation and the involvement of functional bacterial groups in the degradation process. Extensive mineralisation of n-hexadecane was found, but mineralisation of n-octacosane and naphthalene was slow or not significant. The influence of sulphate reduction and methanogenesis was shown. An integrated approach for the determination of natural attenuation, as selected in this study, can verify the process where individual findings are of limited value.

The feeding and respiratory behaviour of zooplankton, in partioular the copepods, was examined and the effect of copper and mercury on their feeding studied. Feeding rate is expressed as the volume swept clear by an animal per day and termed 'filtering rate' or 'grating rate') respiration is expressed as the weight of oxygen used per day by the animals. Preliminary work to derive suitable experimental conditions showed that filtering rates were affected by the number of animals in feeding containers but were apparently unaffected by the size of the feeding container. The longer an experiment was run, the lower were the filtering rates. Respiration rates were not affected by the duration of an experiment or the density of animals in an experimental container. The means of agitation employed during an experiment affected respiration rates but not feeding rates. The gracing and respiration rates of a natural population of copepods from Loch Ewe, Hester Ross, Scotland, grazing in natural population phytoplankton from Loch Ewe were measured at three weekly Intervals throughout 1971. Feeding rates were estimated by measuring changes of ohlorophyll and concentration in the grazed phytoplankton samples: chlorophyll a, gives a good indication of the amount of plant material present in natural sea water. Respiration rates were measured using the Winkler technique. The experiments showed that both feeding and respiration rates, even if corrected for the differences in weight of the animals during the year, rose during the spring outburst in phytoplankton production, fell and then rose again during the second rise in plant production in late late summer. Experiments confirmed that the filtering rates of the copepods rise in response to increased food supplies, although this response may be seasonally adjusted. aWhen the filtering and respiration rates of the copepod were combined with information obtained by other workers at Loch Ewe on primary production and standing stock of particulate carbon and of zooplankton throughout the year, it was found that the experimentally derived filtering rates would enable the copepods to catch enough food to meet their respiratory requirements, except during the winter However, the copepods appeared to have eaten only approximately 40% of the primary production compared with an expected value of twice this percentage. Further studies showed that if the uneven distribution of the animals and plants in the water column were taken into account, the grazing estimate was close to that expected. It was also confirmed that the animals fed at a higher rate on larger particles in sea water. In experiments to determine the effect of heavy metals on the feeding of copepods, it was found that 10 /g copper/litre significantly reduced the copepods' filtering rates in natural and synthetic media. The growth and size distribution of plants in natural sea water grown in the presence of 10 /g copper/litre was also affected. In the presence of a chelating substance, the copper became relatively innocuous even at concentrations higher than 10 g/litre this lends weight to the hypothesis that only ionic copper affects the feeding of copepods and that when it becomes bound to large organic molecules, it becomes harmless. The copepods also recovered from previous exposure to/to copper when they wore removed to fresh sea water, Estimates were made of the likely effect of pollution by copper on the production in a sea Lochs grazing by copepods was estimated to fall by as much as 70% in the presence of 10 /ug copper/ litre. The sources of discrepancies in making these' estimates is' a discussed. 3 g mercury/litre in sea water affected the feeding of copepods, but some difficulty was experienced in measuring the effect on feeding in natural phytoplankton as the mercury seemed to enhance the growth of some phytoplankters in sea water.

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