The 2013 meeting of the Working Group on Ecosystem Effects of Fishing Activities (WGECO) focused its work on the issue of indicators for ecosystem components in the context of the Marine Strategy Framework Directive (MSFD) and, as has been a particular area of study over the last two years, foodweb indicators.
As Descriptor 4 of the MSFD, foodwebs represent one of the most difficult areas to develop indicators for. In 2012, WGECO took the main issue to be that indicators primarily focused on the "structure" of foodwebs rather than the "functioning" or the dynamics of the processes operating within them. After much discussion though, the group found that these two characteristics are really intertwined; variation in the structure of foodwebs invariably alters the dynamics of processes and therefore how they operate. As the functioning of an ecosystem can't really be conserved, there is a need to focus on the structures providing the functions.
This year WGECO began to look at possible structural indicators of foodwebs. Existing indicators largely focus on key species, but the group looked at the possibility of indicators that could integrate more widely. The type of indicators the working group resolved to explore included:
- the distribution of species over body size ranges and hence trophic levels. This was based on the observation that there are many more small bodied species,
- responses of the marine size spectra to pressures,
- the strength of competition amongst species,
- slow responses resulting from interactions amongst functional groups,
- characteristic trophic transfer efficiencies.
The focus was mainly on the first two listed points, with WGECO reporting on the initial steps for the development of an indicator for the distribution of the body masses of species in marine communities, and so possibly also an indicator for the distribution of species richness over trophic levels.
WGECO also looked at the role of zooplankton as well as the significance of whether foodwebs were top-down controlled, with animals highest in the web controlling abundance of their prey, or bottom up, where the availability of food (e.g. phytoplankton) controls the abundance of those who eat it. This is a highly controversial field and any assumption one way or the other can significantly impact on indicators and how they are used.
The finished report will be availble via WGECO's webpage here.
