Impact mitigation in marine and coastal environments: policy challenges and shortfalls

Marine environments are increasingly under threat from the direct impacts of human activity, such as resource extraction and over-exploitation, and indirect threats from land-based activities that lead to pollution, increased nutrients and sedimentation. The need for mitigation of these impacts alongside the continued drive for economic growth has led to policy responses that attempt to build the cost of biodiversity losses into the cost of development. One such policy mechanism is biodiversity offsetting, whereby impacts are sequentially avoided, minimized, restored, and finally offset through the use of the mitigation hierarchy. Biodiversity offsets are increasingly used to mitigate the residual impacts of development on threatened species and ecosystems, in theory allowing development without the associated loss of biodiversity. Most biodiversity offset policy and theory has concentrated on offsetting in the terrestrial environment, while offsets in the marine environment have received little focus.In this thesis, I investigate the extent to which marine and coastal biodiversity offset policies occur globally and examine the complexities and challenges associated with their application. I discuss opportunities for offsets to achieve better outcomes for marine biodiversity, and evaluate the risks involved. Using a mixed method approach, I first identify the most relevant differences between marine and terrestrial environments and the implications of those differences for biodiversity offsetting. I then review the literature on biodiversity offsets to develop a database of offset policies globally that could include marine environments and determine their stage of development (Chapter 2). I find that many countries have policies that could potentially include marine environments. I explore several important practical differences when offsetting in the marine environment, for example greater connectivity both within marine ecosystems and between marine and terrestrial systems, and limited finely-resolved marine data. While these differences have significant implications for offset feasibility and effectiveness, I also identify potential opportunities afforded by the nature of marine systems for offsets to mitigate impacts more effectively, such as allowing more spatial ‘flexibility’ in offset locations. Using the database developed in Chapter 1, I next evaluate the way in which marine environments are included in offset policies globally. I explore the extent to which policies are specifically focussed on or apply to marine environments and their stage of development (from Chapter 2), and identify correlations between these factors and marine biodiversity, as well as political and economic variables, to determine what might be driving this policy differentiation (Chapter 3). I find that while few countries had policies specifically tailored to marine environments, many explicitly state that their offset policy can apply to the marine environment. I find that wealthier countries with more stable governance, but a lower density of threatened marine birds and mammals, were more likely to have better-developed and more marine-specific offset policies.I then further explore the global distribution of pressures on the marine environment, specifically from metals and minerals mining, and identify how these relate to whether current offset policies account for impacts at the land-sea boundary. To do this, I summarise information on the types of mines that occur in coral reef catchments globally currently, and those likely to be developed in the future, and then develop a spatially explicit model of the potential for sediment impacts from terrestrial mining on adjacent coral reefs (Chapter 4). I simulate how existing environmental governance in countries with reef-draining catchments could mitigate risks to coral reefs and find that countries with the highest sediment risk also have relatively poor environmental governance, and less-developed offset policies.Spatial flexibility in offsetting means allowing offset actions to occur far from an impact site, and has been controversial because the requirement for ecological equivalence is often met partly through requiring close proximity between the biodiversity lost from development and the biodiversity gained by an offset. In Chapter 5, I discuss the circumstance where spatially flexible offsets could be more effective for marine biodiversity values than offsetting near to the site of impact, and attempt to model the relative benefits of more or less spatial flexibility in offset location for migratory shorebirds. I find that key data were missing to enable confident estimation of the relative benefits of locating offsets near to and far from the impact sites, even in this relatively well-known system. Further, the risks of allowing flexible offsets, such as reduced ecological equivalence and the challenges of working across geopolitical borders, must be weighed against the potential benefits of offshoring biodiversity.This thesis concludes that the development of offset policies in the marine environment has moved faster than the scientific evidence underpinning their application. It is therefore unlikely that offsets occurring in the marine environment can achieve no net loss without significant changes in the way they are applied. This includes a more rigorous application of the first three stages of the mitigation hierarchy, offset policies that account explicitly for the challenges posed by offsetting in the marine environment, strategic environmental assessments that incorporate indirect and cumulative impacts at a wider geographic scale, and the integration of land-sea planning with biodiversity offset policies to mitigate complex impacts more effectively