- Descriptors of Posidonia oceanica meadows: Use and application

The conservation of the coastal marine environment requires the possession of information that enables the
global quality of the environment to be evaluated reliably and relatively quickly. The use of biological indicators
is often an appropriate method. Seagrasses in general, and Posidonia oceanica meadows in particular, are
considered to be appropriate for biomonitoring because of their wide distribution, reasonable size, sedentary
habit, easy collection and abundance and sensitivity to modifications of littoral zone. Reasoned management, on
the scale of the whole Mediterranean basin, requires standardized methods of study, to be applied by both
researchers and administrators, enabling comparable results to be obtained. This paper synthesises the existing
methods applied to monitor P. oceanica meadows, identifies the most suitable techniques and suggests future
research directions. From the results of a questionnaire, distributed to all the identified laboratories working on
this topic, a list of the most commonly used descriptors was drawn up, together with the related research
techniques (e.g. standardization, interest and limits, valuation of the results). It seems that the techniques used to
study meadows are rather similar, but rarely identical, even though the various teams often refer to previously
published works. This paper shows the interest of a practical guide that describes, in a standardized way, the
most useful techniques enabling P. oceanica meadows to be used as an environmental descriptor. Indeed, it
constitutes the first stage in the process.