Global and Regional Variations in Methane Seep Communities

The increasing focus on exploitation of the deep sea is raising considerable concerns about how these ecosystems will be impacted. There is increasing demands for natural resources to meet human population growth and declining resources on land, which are driving interest in deep sea resources. Deep sea organisms are often slow growing and long-lived, so destructive practices such as trawling and mining have the potential to cause considerable damage. Methane seeps are chemosynthetic ecosystems that rely on the microbial oxidation of methane to provide food for a diversity of fauna, and provide provisioning, regulating and cultural services to society. Despite these ecosystems being identified as vulnerable marine ecosystems by the Food and Agricultural Organisation of the United Nations (FAO), they have limited protection from anthropogenic disturbances. My thesis addresses knowledge gaps on the global bioregional variations of methane seep communities and the regional effects of bottom trawling on methane seep ecosystems. I aimed to understand bioregional patterns of methane seep communities and the effects of trawling, to highlight the global diversity of methane seep ecosystems and provide insight for future management actions and decisions. In chapter two, I conducted a global meta-analysis to examine the bioregional variation in methane seep meiofauna, macrofauna and associated benthic and pelagic communities. I found significant bioregional variation in methane seep communities where methane seeps clustered in the bioregions depicted by Costello et al. (2017). I also found that variations in methane seep communities correlate with changes in depth. My study highlights the importance of understanding methane seep bioregional variations in marine management. Understanding bioregional variations will ensure that there is representation of the diversity within methane seeps, in marine management to avoid biodiversity loss.

In chapter three I studied variations in the benthic and pelagic community at methane seeps on the Hikurangi Margin of New Zealand. I assessed how these variations correlated with depth, trawl intensity, and rugosity to understand the factors driving variations in methane seep communities. I found variation in methane seep communities corresponded with variation in trawl intensity and depth. Increasing trawl intensity corelated with a decrease in the abundance of endemic methane seep taxa (Lamellibrachia tube worms, Calyptogena clams and Bathymodiolus mussels). I also observed that in areas of high trawl intensity methane seep fauna were taking refuge around the carbonate structures at the methane seeps. My results emphasise the need for management plans to be enacted to prevent anthropogenic disturbances to methane seeps. Management of methane seep ecosystems needs to ensure that the diversity of these ecosystems is represented within management plans, to avoid biodiversity loss in the deep sea. To do this management of methane seep ecosystems will need to take a bioregional approach and manage within bioregions at small scales so that the diversity of methane seep fauna is represented.