When reviewing the various fish-based community
indicators aiming at assessing the ecological status of marine communities
and/or ecosystems, a typology consisting of three major components emerges.
The first component highlights the choice of relevant metrics associated
with a level of organization (e.g. population or community). The second
relies on the method used to combine the metrics (an aggregated indicator or
a synoptic table). The third refers to the type of analysis (direct or
indirect) that is used to establish the link between the metrics and a given
pressure. In this paper we use the Vilaine coastal-estuarine fish
communities as a case study to discuss and relate two different approaches
to the suggested typology. The first approach (time-trend approach) is based
on historical series of data, whereas the second approach (multi-metric
index, MMI) is based on a geographic series including various French
estuaries. They were developed or adapted from French studies but are
representative of the approaches used in Europe. When applied to the case
study, they differed in their diagnosis: the time-trend approach indicated
that the bay of Vilaine habitat was deteriorating, whereas the MMI, which
compares many French estuaries, indicated a good environmental state.
Differences and complementarities between the approaches are thoroughly
discussed with respect to the three mains components of the typology. This
work appears at a particular moment, when several fish-based indicators are
being developed in France and the rest of Europe. It intends to serve as an
element of the ongoing reflection concerning the limitations of the various
approaches that can be used to develop such indicators.