The Convention on Biological Diversity (1992) and the more recent EU Marine Strategy Framework Directive (2008) require the conservation, maintenance, sustainable use, and/or improvement of biodiversity. However, little scientific research has been done into how to characterise and manage pelagic (water column) habitats under biodiversity frameworks, not least because of their vast scale and highly dynamic nature. With the Ecosystem Approach becoming an increasingly-applied holistic management mechanism, knowledge gaps such as these hinder the political implementation of conservation and sustainable management for pelagic habitats. In Europe, for example, the Marine Strategy Framework Directive takes an Ecosystem Approach to managing Europe’s seas with the overarching objective of achieving ‘Good Environmental Status’. A vision of what Good Environmental Status (GES) looks like for pelagic habitats and biodiversity, however, has yet to be fully articulated, but is needed to ensure high level management objectives for pelagic habitats are applied in an ecologically-meaningful manner.

To begin to address this challenge, Mark Dickey-Collas (ICES), Verena Trenkel (Ifremer), and I convened an open theme session at the 2016 ICES annual scientific conference entitled “What is a good pelagic habitat?” Here we tackled some high level questions around what the concept of ‘good’ looks like in pelagic habitats, how we can assess their quality to guide management, and how biodiversity can be considered in pelagic habitats, with their highly dynamic natures.

Three high level criteria can be used to help articulate Good Environmental Status for pelagic habitats.

We found that for pelagic habitats to reflect Good Environmental Status they must be able to provide ecosystem services (biodiversity, carbon cycling, food provision through supporting marine food webs). We came up with three general criteria that can be used to articulate the concept of ‘good’ pelagic habitats:

1. The pelagic habitat must be in suitable condition so that it can support the normal functioning of all species who use it, whether they spend their whole life cycle, or just part of their life cycle, in the water column
2. The pelagic habitat maintains normal biogeochemical functioning, which supports carbon and nutrient cycling and gas regulation
3. The physical qualities of the pelagic environment, including movement of water masses and marine organisms at multiple scales, are allowed

These three criteria allow consideration of the pelagic habitat to be based on hydrography, rather than geography. In other words, instead of defining Good Environmental Status for a place or time, what if we define it as demonstrating the above properties instead? The details surrounding GES (indicators, targets) could then vary nationally or regionally but would be in alignment with these overarching conditions. For all three to be achieved, the connection between human pressures on the marine environment and oceanography would have to articulated.

Because these are high level criteria, further work is needed to understand how to translate them fully into operational management frameworks that can actually be used to manage pelagic habitats. For example, there are still critical questions around what biodiversity means for pelagic habitats, how this can be understood through the use of plankton indicators, understanding the spatial and temporal variability in these concepts, and, critically, how this complex information can be best used to underpin marine management decisions.

Abigail, Plankton and Policy

Read more: Dickey-Collas, M., McQuatters-Gollop, A., Bresnan, E., Kraberg, A.C., Manderson, J.P., Nash, R.D.M., Otto, S.A., Sell, A.F., Tweddle, J.F. and Trenkel, V.M., (2017). Pelagic habitat: exploring the concept of good environmental status. ICES Journal of Marine Science, 74: 2333-2341.