The detection of anthropogenic impacts in our estuaries has become a critical social, political and scientific concern in recent years. Work has focussed on the effects of these impacts on the spatial and temporal patterns of biotic assemblages and searched for bioindicators and biomarkers of pollutants that may act as early warning signs. The estuaries in temperate Southeastern Australia have a diversity of biotic assemblages living in the soft sediment. One of the most abundant macroinvertebrates is the little studies mussel, Xenostrobus securi that is found living with an assemblage of benthic biota including amphipods, crabs, isopods and tanaids, bivalves and gastropods. Two commercial fish species bream and mullet also inhabit these estuaries. Numerous stormwater drains can be found entering the estuaries through the mangrove forests lining the shores. Along with inputs of freshwater, stormwater drains are thought to be responsible for the entry of heavy metals into estuaries. These heavy metals have the potential to alter the patterns of biotic assemblages and bioaccumulate in the tissues of miacroinvertebrates, mussels and fish living within temperate estuaries. Over the time of this study the concentrations of heavy metals in the sediment tissues and shell of X.Securis varies spatially and temporally. Although this study adds substantially to current knowledge there is still more that is needed to establish X. Securis as a bioindicator. Questions remain about uptake, depuration and response to environmental gradients of heavy metals in X. Securis. Before X Securis can be used routinely in monitoring heavy metal contamination these questions need to be further investigated / Doctor of Philosophy (PhD)

Thesis (M. Phil.)--University of Hong Kong, 1999. / Includes bibliographical references (leaves 119-129).

M.Sc. / A lot of research in ecotoxicology is currently focused on identifying and developing suitable biomarkers for use in assessing the health of aquatic systems. Thus this study was done as part of a major project aimed at identifying and selecting suitable biomarkers to use in the Rietvlei System, South Africa. This study focused on the response of Clarias gariepinus (Burchell, 1822) to contaminants using three biomarkers: population genetic structure, DNA damage and metallothioneins (MT¡¦s). The main objectives of the study were to assess the potential of these biomarkers in C. gariepinus and to provide baseline data on the Rietvlei System. Eighteen enzyme loci (creatine kinase (Ck), esterase (Est), phosphoglucomutase (Pgm), glycerol-3-phosphate dehydrogenase (G3pdh-1 and -2), glucose-6-phosphatase isomerase (Gpi-A and -B), L-lactate dehydrogenase (Ldh-A and B), malate dehydrogenase (sMdh-1, -2 and -3), malate dehydrogenase (NADP+) (Mdhp), phosphogluconate dehydrogenase (Pgdh), isocitrate dehydrogenase (NADP+) (Idh); superoxide dismutase (Sod), and peptidase: substrate (leucyl tryrosine) (Pep-S1 and -2)) were screened for by horizontal starch gel electrophoresis. An agarose gel electrophoretic method was used for DNA damage determination and a spectrophotometric method for metallothionein. The Rietvlei System population (RSP) showed higher genetic variability as shown by the average number of alleles per locus (A), proportion of polymorphic loci (P) and expected average heterozygosity (HE) than the reference populations. Statistically significant deviations (p < 0.05) from Hardy-Weinberg proportions associated with heterozygote deficiencies occurred at Gpi-B, Idh, Pgdh, Ldh-A and Pep-S1 for RSP. These deviations could have been a result of small sample size. There was high genetic differentiation between RSP and the reference populations with FST values of 0.450 and 0.480 between RSP and wild population (WP) and RSP and Northern Cape population (NCP) respectively. A mean base-pair length of 6770.9 „b 10.68 (SE) bp was recorded in the Marais Dam population (MDP) that of 6327.2 „b 17.69 (SE) bp was recorded in the Rietvlei Dam population (RDP). The MDP had a higher proportion of DNA fragments with low base-pair lengths than RP indicating a higher level of DNA damage. The level of DNA damage in the MP was higher than in the RDP. The mean MT¡¦s content was 3.63 „b 0.643 (SE) nmol g-1 wet weight in the MDP and 4.35 „b 0.580 (SE) nmol g-1 wet weight in the RDP. There was no significant (p = 0.40) difference in the levels of MT¡¦s between the two dams. It was concluded that there were significant differences in genetic diversity between RSP and the other populations in unpolluted sites; hence genetic diversity in C. gariepinus has potential as biomarker of pollution. However, further research is recommended to investigate possible contributing factors to differences in genetic diversity such as inter-sex males, geographical isolation and differences in sample sizes used. DNA damage is also a potential biomarker provided due care is taken in interpreting average base-pair length data to consider differences in each DNA size class. It seems further research is required before conclusions are made about use of MT¡¦s as biomarker in this population. The levels of MT¡¦s in other uncontaminated systems will be useful to determine whether the levels recorded in this study are background levels or responses to contamination. / Prof. F.H. van der Bank

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