Oxidative damage and antioxidant metabolism of Ulva pertusa and the associated grazer Micrelenchus tenebrosus in response to fluoranthene exposure

Abstract

Coastal marine systems are both ecologically and economically important worldwide, yet over the last few decades these environments have become increasingly impacted by contaminant inputs, particularly from urban runoff, industrial discharge and marine traffic. Some of the most prevalent contaminants of the coast are Polycyclic Aromatic Hydrocarbons (PAHs), originating from diesel fuels, sewage and as products of industrial incineration. Low level concentrations of PAHs continuously enter populated coastal areas, fluoranthene (FLA) being one of the most common. Ulva spp are cosmopolitan marine macroalgae and are often the trophic base of ecologically diverse coastal systems, providing food, shelter and breeding grounds for many coastal marine organisms. Ulva spp are typically very hardy, existing in nutrient deficient and rich waters throughout low to high gradients of pollution. The aforementioned attributes, along with its easy accessibility and structural uniformity (single cell type), make Ulva spp ideal candidates for PAH monitoring. Little research exists on the biochemical changes occurring in seaweed exposed to PAH pollutants and their potential use as a monitoring tool. This thesis explores that possibility by analysing biochemical changes, in the form of oxidative stress, macromolecule damage and antioxidant responses in Ulva pertusa exposed to four environmentally relevant concentrations of FLA, ranging from constant low level input concentrations (0.01nmol/l) to extreme solitary-event levels (10nmo/l). All FLA exposure induced some production of reactive oxygen species (ROS) and subsequent up-regulation of many key antioxidants and enzymes including: catalase (CAT) ascorbate (AsA), ascorbate peroxidase (APX), mono-dehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR) and glutathione S-transferase (GST). Additionally, U. pertusa accumulated FLA in its tissue and was unable to recover from damage incurred at high FLA exposure (10nmol/l), while all U. pertusa exposed to lower concentrations recovered after a few days. The ecological importance of Ulva spp to other trophic level species prompted an investigation into the effect of three varying levels of FLA contamination (0.01, 0.1 and 1nmol/l) on an associated gastropod grazer (Micrelenchus tenebrosus). This was conducted under two independent contaminant regimes: the first being seawater contamination with U. pertusa as a food-source, the second; grazing of FLA contaminated U. pertusa in uncontaminated seawater. Both contaminant regimes produced an increased level of cellular FLA in the grazer, where levels increased according to concentration and duration of iv exposure. Interestingly, M. tenebrosus grazing on contaminated U. pertusa accumulated 2-3 times more FLA than specimens exposed to contaminated seawater alone. Both contaminant regimes caused oxidation of lipids, proteins and DNA in M. tenebrosus and the up-regulation of antioxidants, including: CAT, glutathione (GSH), glutathione peroxidase (GPX), glutathione reductase (GR) and GST. Levels of antioxidant and enzyme activity were again higher overall in snails under the food-source contamination regime, suggesting dietary uptake of FLA by grazing invertebrates enhances its toxicity to the consumer. In conclusion the antioxidant activity of both seaweeds and grazing invertebrates may be useful bioindicators for future monitoring of coastal marine PAH contamination globally.