Sentinel Species - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 177

amphipods, whereas they wondered at the absence of some taxa such as the aquatic oli-
gochaetes or the chironomids (midge larvae), and at the low representation of fish. In the
same work, they regret that too many tested species are more marine than estuarine, and
that allowances for salinity levels are insufficient. Authors too often try to fit the salin-
ity of a sediment to the available model species, thereby modifying the physicochemical
forms of pollutants and therefore their bioavailability and potential toxicity, rather than
testing the relevant sediment while maintaining its initial physicochemical characteristics,
and selecting the species to be tested on these criteria. Chapman and Wang (2001) thus
end on the necessity to develop studies of this physical compartment in estuaries, regions
that are particularly subjected to anthropogenic contributions, often in complex mixtures,
and to pay more attention to the physicochemical conditions of the laboratory tests in
order to be able to compare the laboratory results to those in situ with more justification.
In this perspective, few endobenthic estuarine species have been selected as biological
models in ecotoxicological programs, typically the ragworm Nereis diversicolor and the
bivalve Scrobicularia plana , which are indeed keystone species of the estuarine ecosystem.
With the aim of a general appreciation of the quality of the estuarine environments, these
two deposit feeding estuarine invertebrates appear as an interesting complement to filter
feeders representative of the quality of the water column, allowing a wider appreciation
of the contamination of sediments in situ , and over relatively long periods (Moreira et al.
2006; Poirier et al. 2006; Coelho et al. 2008; Sole et al. 2009; Fossi Tankoua et al. 2010, 2012).
In Quebec, it is a suspension feeding endobenthic bivalve mollusk, Mya arenaria , which
has been retained as sentinel species (Siah et al. 2003; Frouin et al. 2007; Gagné et al. 2009).
Indeed, ubiquitous in the northern hemisphere (through anthropogenic introduction), this
clam, besides its local economic interest, plays a key role in estuarine food webs in Quebec.
Among fishes, the European eel, Anguilla anguilla , a bottom-dwelling species has been
chosen by Piva et al. (2011) and Benedetti et al. (2012) as a sentinel species for assessing
sediment quality because of its frequency in European estuaries, brackish and freshwater
basins, and its tolerance to a wide range of biotic and abiotic factors. Moreover, ecotoxico-
logical studies have shown their capacity to accumulate elevated concentrations of chem-
icals due to their high lipid content (Maes et al. 2005; Belpaire et al. 2011), and several
biomarkers have been characterized that respond in this fish to the main classes of envi-
ronmental pollutants (Van der Oost et al. 1996; Valbonesi et al. 2011).
7.3 Species Used as Sentinels
Many species, animal or plant, can be used to provide indications on the quality of the
environment, but their performance and hence suitability in this role may well turn out to
differ according to the biomarker chosen. This factor, added to the list of criteria already
evoked in the choice of a sentinel species, may further quickly limit the choice for a par-
ticular objective (Depledge and Hopkin 1995; UNEP/RAMOGE 1999).
In a review on the use of MT as a biomarker, Amiard et al. (2006) show that for this
biomarker, three taxa of invertebrates are mainly used in coastal and estuarine regions
where they play key roles: mollusks, crustaceans, and annelid worms. Figure 7.7 shows
that among the mollusks, it is the bivalves that are mostly used in this role (65%), whereas
decapods dominate the crustaceans (70%), and polychaetes are the annelids most often
quoted (81%).