Combining bioturbation and redox metrics: Potential tools for assessing seabed function

Abstract

Current national (e.g. UK Marine and Coastal Access Act) and international (e.g. Water Framework Directive, Habitats and Bird Directives, European Marine Strategy Framework Directive) legislation and the recent UK state of the seas report Charting Progress 2 have focused on the quality and status of the marine environment. To this end, the UK has continued to work on the need to develop indicators which can assist with this process. This work has helped to identify the natural processes and man-made activities that are affecting marine systems. One of the marine descriptors within the MSFD is ‘seabed integrity’. This descriptor asks member states to ensure that the structure and function of ecosystems are safeguarded and benthic systems are not adversely affected. To date, we have furthered our understanding of the seabed by, for example, studying benthic systems. For this purpose indicator tools, such as a suite of benthic indices, have been employed as measures of ‘the health of benthic systems’. In most cases this information mainly relates to the structure of benthic populations. However, there is a gap in terms of what we can measure with regards to the function of the ecosystem and how individual benthic animals perform their roles within specific ecosystems. There is also a lack of data to assess if the functions of the seafloor are safeguarded. This work has combined two metrics, bioturbation potential (Bpc) calculated from quantitative information and apparent redox discontinuity layer (aRPD) derived from SPI images. Results indicated that both metrics provide valuable complementary information. The aRPD informed on the status of the sedimentary environment and these values were easily related to Bpc values. The Bpc values were used to quantify bioturbation activity and species’ identity at each site. The link between aRPD and Bpc can allow characterisation of 4 conceptual areas in relation to a key sediment function such as to carbon and nutrient cycling rates and control areas.