Benthic indicators and index approaches in the three main estuaries along the French Atlantic coast (Seine, Loire and Gironde)

Abstract

The three main estuaries in the French Atlantic coast – the Seine, Loire and Gironde, all with high tidal regimes – are interfaces between the continental and the coastal ecosystems. The Seine and Gironde are highly contaminated, whereas the Loire remains in a more natural state. Both the Seine and Gironde have suffered from harbour construction, and as a result, their biological units are extremely compartmentalized. Benthic species and communities have adapted to tolerate temporal physical and chemical changes (e.g. salinity, substrata, depth, and levels of fine particles and oxygen) and human activities (e.g. dredging, shipping traffic, and habitat reduction). Although numerous bio‐indicators and indices are used to define the ecological quality status (EcoQS) of coastal waters, very few of them were developed specifically for environments with a mosaic of conditions and salinity levels, including freshwater. The main problem appears to be that all the indices for determining anthropogenic stress examine the abundances of stress‐tolerant species, which may also be able to tolerate natural stressors such as those occurring in estuaries. This paper takes a look at the development status of the benthic indicators and index approaches used in the three main estuaries along the French Atlantic coast. In addition, it examines the adaptation of the different benthic indicators to the taxonomic sufficiency principle, and the adaptation of the Benthic Opportunistic Polychaetes Amphipods index (BOPA) and the Benthic Opportunistic Annelida Amphipod index (BO2A) for use in the freshwater zones of transitional waters (i.e. up to the upper limit of the tidal range). Several perspectives are discussed in light of the diverse disturbances and the heterogeneity of such stressed zones, such as the use of multimetric and scoring approaches.

Performance comparison of biotic indices measuring the ecological status base on soft-bottom macroinvertebrates: a study along the shallow Gomishan lagoon (Southeast Caspian Sea)

“…Many researchers (LABRUNE et al, 2006;BLANCHET et al, 2008;BAKALEM et al, 2009;DAUVIN et al, 2009;GRÉMARE et al, 2009;RANASINGHE et al, 2009) have highlighted the differences in assessments produced by the various benthic indicators. These differences are caused by several things, in particular by the fact that the indicators do not use the same method for species classification (e.g., the AMBI classifies species into Ecological Groups following PEARSON and ROSENBERG's concept.…”

Local changes in copepod composition and diversity in two coastal systems of Western Europe

“…1 149 s -1 and 342 m 3 s -1 , respectively) act on the growth of estuarine species in oligo-and mesohaline water 150 masses. In this naturally stressed environment (Dauvin et al, 2009), an increasing gradient of 151 zooplankton diversity is observed from the upstream to the downstream areas (Sautour and Castel, 1995; 152 Chaalali et al, 2013a).…”

Regional-scale analysis of subtidal rocky shore community

“…Conversely, in very turbid sites (sites 1, 20, 30, and 35, all grouped in cluster B of the cluster analysis), kelp species were absent; in those places, kelp was replaced by other algae (Halidrys siliquosa, Sargassum muticum, and Solieria chordalis) that were adapted to highly turbid water (Dring 1987;Castric-Fey et al 2001). In Southern Brittany, the Gulf of Morbihan and the Vilaine and Loire estuaries provide suspended matter and nutrients that also cause increased turbidity (De Roeck unpublished data; Dauvin et al 2009;Lazure et al unpublished data); that turbidity may form the basis for the lower kelp density observed in this area, even at open-sea sites. Turbidity measurements (Teissier 2006;Méléder unpublished data;EUSeaMap unpublished data) have demonstrated that the waters around the Vilaine and Loire estuaries contain high quantities of suspended matter, often 10-60 nephelometric turbidity units [NTUs], and sometimes up to 100 NTUs.…”