Abstract
Anthropogenic pollution is a growing concern, damaging the natural environment and the organisms that live in it. Plastic entering the oceans, which does not readily break down and persists long term, has been observed to be ingested by multiple marine taxa. Furthermore, the efficiency of plastic to adsorb and contain persistent organic pollutants and heavy metals adds an additional threat following ingestion. Plastic alternatives have been developed, from composting and biodegradable material to edible films and biopolymers, but there has been little research on what happens to these petroleum plastic alternatives if they end up in the marine environment. Do these plastic alternatives fix the problem that plastic creates, create a new problem that is not yet studied, or do they cause an equal amount of damage? The overarching aim of this MSc thesis was to examine whether exposure to petroleum derived microplastics (PMP) and biopolymer microplastics (BMP) would impact the fitness of a cryptobenthic fish (Forsterygion capito, mottled triplefin fish), using a series of behavioural and physiological endpoints. In Chapter Two, I used habitat selection as an indication of behavioural impairment, observing that habitat choice behaviour was significantly affected after exposure to PMPs, with this treatment group selecting simpler habitat compared to controls and fish exposed to BMPs. Maladaptive habitat selection could have downstream effects on reproduction and predation rates, although these were not tested in the present thesis. Behaviour changes are often underpinned by physiological changes, and so I examined levels of serotonin and dopamine using an enzyme-linked immunosorbent assay (ELISA) in an attempt to link changes in neurochemistry with observed behaviour changes. Interestingly there were significant increases in dopamine levels for both the PMPs and BMPs treatment, yet little change in serotonin in the same treatment groups. However, it was difficult to determine the mechanisms underpinning these changes owing to a lack of published literature using a similar experimental approach to the present thesis. Whilst this does demonstrate that this research is highly novel, it did make it difficult to draw conclusive links between the two assays (both behaviour and neurochemistry). In Chapter Three, I further explored the cost of exposure to PMPs and BMPs by examining oxidative stress biomarkers in white muscle. Overall, I found significant increases in antioxidant enzymes indicating exposure to PMPs and BMPs has a negative effect on the health of F. capito. Yet, in spite of increasing antioxidants deployed to neutralise reactive oxygen species, oxidative damage still occurred indicating that cellular damage had occurred. Mounting an antioxidant response isan energetically expensive process that comes at a cost to other fitness enhancing attributes such as growth and reproduction.
Overall, I found that exposure to PMPs and BMPs both led to negative effects on behaviour and physiology in F. capito. Although, F. capito is not a commercially or culturally important fish, it is trophically important and losses in population numbers of trophically important species can ripple throughout food webs. The results presented in this thesis provide compelling evidence that both PMPs and BMPs can negatively affect marine fish. Determining which plastic type is the most damaging to marine taxa is important if we hope to understand and reduce the impact of plastic pollution in marine environments. As such, this research potentially has broad reached implications not only in New Zealand but globally.