Monitoring Shallow Methane‐derived Authigenic Carbonate: Insights from a UK Marine Protected Area

Methane-derived authigenic carbonate (MDAC) is a biogenic rocky substrate formed by microbial assemblages below the seabed. It performs important ecosystem functions, including the provision of reef-like habitats on soft sediments and the sequestration of carbon. The protection of MDAC is limited at the global scale; however, 27 marine protected areas (MPAs) have been designated in European waters for 'cold seep' MDAC, mainly in shallow waters (<200 m). Few studies have been conducted on these habitats from a conservation perspective. The effective management of MDAC structures requires an understanding of their ecology and physical characteristics in a healthy condition. This is best achieved using a multidisciplinary approach to provide evidence on predefined aspects of MDAC structures, termed feature attributes, which can be assessed to determine habitat condition over time. This article presents the first UK effort to develop a multidisciplinary approach to monitoring shallow MDAC feature attributes, using the Croker Carbonate Slabs Special Area of Conservation (SAC) as a case study. A range of remote and physical survey methods were used to characterize the MDAC and associated relatively unimpacted and healthy biological communities. The data confirm that the SAC contains the largest known area of shallow MDAC in European waters, that methane release is ongoing, and that MDAC is still likely to be forming. Specialized chemoautotrophic fauna were not recorded, possibly due to the dominance of fauna that derive carbon (ultimately) from photosynthesis. Five epifaunal taxa were found to be associated with MDAC, but not with the surrounding sediments. The broad multidisciplinary survey allowed a detailed characterization of shallow MDAC but was resource intensive. We recommend a low-resource monitoring strategy to deliver cost-effective and robust evidence for condition assessment and suggest further studies to contextualize future interpretations of change.