The role of oxidative stress in the reproductive fitness of marine invertebrates exposed to environmental stressors

by Kathryn Naomi Lister

Institution: University of Otago
Year: 0
Keywords: Oxidative stress; Antioxidant; Pollution; Life history; Antarctica; Echinoderm
Record ID: 1300953
Full text PDF: http://hdl.handle.net/10523/5444


Coastal marine environments have become increasingly impacted by anthropogenic contamination, particularly from industrialisation, agricultural run-off and marine traffic. It is essential that we better understand the underlying mechanisms of toxicity that these pollutants pose to natural populations of marine species. Oxidative stress (OS) in organisms occurs when the rate of reactive oxygen species (ROS) generation exceeds the scavenging capacity of an organism’s antioxidant (AO) system and is an important unifying feature underlying the toxicity of many chemical contaminants in aquatic organisms. Oxidative stress is also thought to be a possible mediator of trade-offs between current and future reproduction. The studies included in this thesis utilized AO enzyme activities, levels of the molecular antioxidant glutathione, protein carbonylation, lipid peroxidation and levels of 8-OHdG in DNA as OS biomarkers in a range of marine invertebrates. The objectives were to evaluate the general effectiveness of these biomarkers for detecting contaminant stress and, more specifically, to assess the reproductive impacts of contaminant-induced OS using sea urchins as a model system. Antioxidants and oxidative damage were shown to be significantly elevated in Austrovenus stutchburyi (Bivalvia: Veneridae) and Micrelenchus tenebrosus (Gastropoda: Trochidae) from a contaminated site in Otago Harbour, New Zealand and in Laternula elliptica (Bivalvia: Laternulidae) and Sterechinus neumayeri (Echinoidea: Echinidae) from a contaminated site in McMurdo Sound, Antarctica when compared with levels in individuals collected from clean reference sites in both locations. Contaminants at these sites predominantly included heavy metals and polycyclic aromatic hydrocarbons (PAHs). The same trends were observed in laboratory experiments in which the New Zealand sea urchin Evechinus chloroticus (Echinoidea: Echinometridae) was exposed to dietary PAHs, specifically phenanthrene, fluoranthene, pyrene and benzo[a]pyrene, indicating that these chemical contaminants had the capacity to induce OS in this species. All biomarkers that were tested proved to be useful indicators of contamination exposure although, in general, oxidative damage showed the greatest sensitivity as a diagnostic measure. To explore the physiological and ecological costs of such contaminants, later experiments assessed correlations between OS status and core components of fitness including reproductive effort, gamete quality and the carry-over potential from parent-to-offspring in E. chloroticus and S. neumayeri. Contaminant exposure resulted in oxidative damage in the reproductively mature gonad tissues of these sea urchins despite a significant upregulation of AO defences, however oxidative damage to eggs for both species was generally negligible, demonstrating that damage measured in the gonad was predominantly occurring in immature ova and/or somatic tissues. Sperm had negligible concentrations of the majority of antioxidants, and experienced greater levels of DNA damage…