Keeping the coastlines of the Southern Ocean pest-free : hazards, risks and management of non-indigenous species in high latitude marine environments

Invasive species are a prominent threat to global biodiversity. In the marine environment of the Southern Ocean, the rate of delivery, establishment and the subsequent impacts of non-indigenous species remains poorly understood. Furthermore, the absence of dedicated monitoring and effective baselines makes it difficult to recognize the presence of invasive populations. It is now understood that several introduction pathways capable of delivering marine species operate in this region, and the first introduced marine species in the Antarctic continent was recently reported. By analysing various stages in the transport pathway, this work provides key information to supplement our current understanding of this threat. In the Southern Ocean, the natural transport mechanism for shallow-water marine organisms provided by kelp rafts is being augmented by plastic debris and shipping activity. Plastic debris provides additional opportunities for dispersal of invasive organisms, but these dispersal routes are passive, dependent on ocean currents, and already established. In contrast, ships create novel pathways, moving across currents and often visiting many locations over short periods of time. Vessel traffic thus poses the most likely mechanism by which exotic species may be introduced to the Southern Ocean. While this hazard incorporates a variety of specific mechanisms such as ballast water, entrained objects and hull fouling, an assessment of these pathways demonstrates that hull-fouling communities are the most likely avenue for marine introductions. Introductions can also occur at the level of the genotype. Remote populations of Mytilus galloprovincialis (blue mussels) from the New Zealand sub-Antarctic islands possess a unique genetic structure and should be considered as a sub-species within the Mytilus complex. Such populations represent valuable examples of genetic information in a species with a genetic structure clearly homogenized through human transport opportunities. These unique populations are at risk of hybridization with cosmopolitan gene-lines sourced from temperate ports. The ability of invasive species to gain rapid anthropogenic dispersal also threatens the genetic diversity of the entire species. This loss of genetic diversity is an additional component of biodiversity loss associated with the spread of non-indigenous species. By identifying high risk species, surveillance and monitoring activities can focus upon species of concern allowing resources to be allocated more efficiently. Temperate fouling communities were collected on settlement plates and exposed to thermal conditions replicating Southern Ocean environments to determine high risk species. A wide variety of temperate species survive the thermal conditions of the sub-Antarctic islands and at least eight species can survive in the waters of Antarctica. Three species (Halicarcinus innominatus, Petrolisthes elongatus and Mytilus galloprovincialis) are capable of spawning and completing their entire life-history cycle at Southern Ocean temperatures. The data collected in this thesis have been incorporated into an assessment of the risk of marine introduction to the sub-Antarctic Macquarie Island Marine Park. Analyses of environmental tolerances show that at least seven species of invasive marine pests, resident in ports in Australia and New Zealand, could potentially survive and complete their life cycles in the water temperatures that are found at Macquarie Island. Management recommendations include the instigation of baseline monitoring programs and operational procedures aimed to minimize the ship-based transport of marine species.