| dc.description.abstract | Polar marine ecosystems may have higher sensitivity to plastic pollution than other regions owing to the system’s physical and biological characteristics e.g., presence of ice and high UV radiation, and weak genetic differentiation of resident biota. In this thesis, I address key knowledge gaps related to the vertical flux of microplastic and impacts of nanoplastic on key species within the Southern Ocean ecosystem. Potential exposure risks and species-specific vulnerabilities to micro- and nano-plastic in polar marine ecosystems, as well as the potential cumulative effects with human-induced chemical and climate stressors were determined from published literature. From this review filter-feeding organisms with known vulnerabilities to changes in their habitat, namely Antarctic krill (Euphausia superba, hereafter krill), were identified for multi stress exposures under controlled incubation conditions. Following this, I undertook incubation experiments and field observations to assess the prevalence and pathways of plastic pollution in the Antarctic marine environment and its impacts on krill. Sampling of microplastic in the Southern Ocean is predominantly focused on the accessible surface waters. I investigate the unexplored vertical flux of microplastic in the Southern Ocean water column, demonstrating that the top 150 m of the water column can act as a conduit for microplastics away from the surface. Plastic flux was found to be greatest in the top 50 m, which coincides with the preferred feeding depths of zooplankton. From a biological standpoint, this thesis is focused on the smallest and potentially most hazardous plastic pollutant, nanoplastic, and its impact on the keystone species of krill. Results herein demonstrate that the embryonic development of krill over a six-day exposure (selected based on the average krill hatch time) is significantly less (tested with a binomial generalised linear model) in a multi-stress nanoplastic and ocean acidification scenario compared to the control, which is not apparent when considering the stressors singularly. In further experiments, I show that nanoplastic does not impact key energy reserves (total lipid, or fatty acid composition) in krill embryos across maternal (~48 hours) or direct embryo (6 day) exposures. However, the effect of described multi-stress scenarios on lipid reserves is yet to be explored. This thesis concludes with an optimised method, developed for characterising microplastics from multiple Antarctic sea ice cores with automated Focal Plane Array micro-Fourier Transform Infrared (FPA μFTIR) analyses. The protocol presented here fills a key research gap and will enable better understanding of the interactions of plastic pollution and sea ice, and how these may impact species dependent on sea ice.
Collectively, my results presented here provide insight into addressing exposure and risks of micro- and nano-plastic to vertically migrating and sea ice dependent species in the Antarctic marine ecosystem. Further, results highlight the need to consider the species impact of plastic pollution from a multi-stressor standpoint. The findings are an important contribution to the growing evidence base that is required to develop/advance an environmentally relevant framework for the protection of sensitive polar ecosystems. | en_GB |
