Introduction - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 9

2007; Romeo and Wirgin in Amiard-Triquet et al. 2011). In contaminated areas, an increased
frequency of resistant genotypes has often been reported, allowing the maintenance of
DNA integrity associated with the duplication of specific genes (Figure 1.5). However,
negative consequences of being resistant may be observed, such as decreased fitness and
decreased adaptability to new environments or stressors, thus increasing the probability
of local extinction (Chapter 14).
Biomarkers are available as crucial tools in ecotoxicology, because they can be used as
early warning signals of environmental change before the onset of irreversible damage
at the population level. Syntheses published at the turn of the century (Lagadic et al.
1997, 1998; Garrigues et al. 2001) suggested that scientists were then ready to transfer the
methodology of biomarkers to end users in charge of environmental biomonitoring. A
decade later, certain biomarkers are used to assess the health status of aquatic environ-
ments in different parts of the world (Chapter 15). However, this use is generally limited
to a relatively small number of more or less specific biomarkers, the worst counterex-
ample being the WFD—a very important regulation aiming at the protection of aquatic
environments from the river source to the seashore—which totally ignores the use of
biomarkers despite the efforts of European scientists to demonstrate the relevance of bio-
markers as tools for the implementation of the WFD (Allan et al. 2006; Hagger et al. 2008;
Sanchez and Porcher 2009). Independently of regulatory frameworks, many important
studies have demonstrated “the usefulness of applying a large array of various combined
biomarkers at different levels of biological organization, in assessing the toxic effects of a
mixture of pollutants in a natural aquatic environment” (Huadi River, a tributary of the
Pearl River, China) (He et al. 2011). In the Bay of Cadiz, biomarkers determined in caged
clams Ruditapes philippinarum allowed assessment of chemical exposure and sediment
quality (Ramos-Gómez et al. 2011). In the Río Champotón (southwestern Mexico), a set of
biomarkers determined in a native fish Astyanax aeneus was shown to be a sensitive and
effective tool for identifying periods of environmental conditions adverse to fish health
(Trujillo-Jiménez et al. 2011).
Several problems contributing to limit the use of biomarkers have been recognized: the
problem of confounding factors (e.g., Thain et al. 2008; Martínez-Gómez et al. 2010),
the question of a reference site, and the lack of ecological relevance (Forbes et al. 2006).
The problem of confounding factors was well conceptualized by Cairns (1992). When a
biological parameter is highly fluctuating, the occurrence of a stress may be concealed
by natural fluctuations. On the other hand, when background values are relatively stable,
any change due to contamination factors is easily revealed (Figure 1.6). As already men-
tioned by Kalman et al. (2010), “The question of confounding factors is well mastered in
biomonitoring programs based on the determination of contaminants in the tissues of
bioaccumulators such as the bivalves used in the 'Mussel Watch'-type programs.” The lit-
erature indicates that the same natural factors are at work in the case of biomarkers (Thain
et al. 2008). Consequently, in the objective of using a peculiar species as a model for the
determination of biomarkers, it is still indispensable to determine the natural fluctuations,
as exemplified for worms (Kalman et al. 2010), bivalves (Burgeot et al. 2010; Fossi Tankoua
et al. 2011), and fish (Sanchez et al. 2008). Temporal surveys provide significant advantages
over spot sampling techniques, allowing the assessment of pollution trends responsible
for population changes while providing data on background levels that would be of great
use in case of a future accident, as often experienced for oil spills (Martínez-Gómez et al.
2010).
For many aspects of environmental monitoring, our present state of knowledge and
the insufficiency of background data available mean that the use of a reference site for