Assessing the environmental status of selected North Atlantic deep-sea ecosystems

The deep sea is the largest biome on Earth but the least explored. Our knowledge of it comes from scattered
sources spanning different spatial and temporal scales. Implementation of marine policies like the European
Union’s Marine Strategy Framework Directive (MSFD) and support for Blue Growth in the deep sea are therefore
hindered by lack of data. Integrated assessments of environmental status require tools to work with different and
disaggregated datasets (e.g. density of deep-sea habitat-forming species, body-size distribution of commercial
fishes, intensity of bottom trawling) across spatial and temporal scales. A feasibility study was conducted as part
of the four-year ATLAS project to assess the effectiveness of the open-access Nested Environmental status
Assessment Tool (NEAT) to assess deep-sea environmental status. We worked at nine selected study areas in the
North Atlantic focusing on five MSFD descriptors (D1-Biodiversity, D3-Commercial fish and shellfish, D4-Food
webs, D6-Seafloor integrity, D10-Marine litter). The objectives of the present study were to i) explore and
propose indicators that could be used in the assessment of deep-sea environmental status, ii) evaluate the
performance of NEAT in the deep sea, and iii) identify challenges and opportunities for the assessment of deepsea
status. Based on data availability, data quality and expert judgement, in total 24 indicators (one for D1, one
for D3, seven for D4, 13 for D6, two for D10) were used in the assessment of the nine study areas, their habitats
and ecosystem components. NEAT analyses revealed differences among the study areas for their environmental
status ranging from “poor” to “high”. Overall, the NEAT results were in moderate to complete agreement with
expert judgement, previous assessments, scientific literature on human-pressure gradients and expected management
outcomes. We suggest that the assessment of deep-sea environmental status should take place at habitat
and ecosystem level (rather than at species level) and at relatively large spatial scales, in comparison to shallowwater
areas. Limited knowledge across space (e.g. distribution of habitat-forming species) and the scarcity of
long-term data sets limit our knowledge about natural variability and human impacts in the deep sea preventing a more systematic assessment of habitat and ecosystem components in the deep sea. However, stronger crosssectoral
collaborations, the use of novel technologies and open data-sharing platforms will be critical for establishing
environmental baseline indicator values in the deep sea that will contribute to the science base
supporting the implementation of marine policies and stimulating Blue Growth.