Sentinel Species - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 157

7.1.1 Development of Concept and the Species Used
The notion of sentinel species has existed for a long time: in the nineteenth century, miners
took a canary with them down into a mine. The appearance of symptoms of asphyxiation
in the bird warned them of the presence in the subterranean galleries of dangerous con-
centrations of toxic gas. The use and the definition of the term of “sentinel species” evolved
over time, and in different contexts, explaining why today there are disagreements and
differences in the use of the concept of sentinel species between authors. Phillips (1994)
considered that species used for biomonitoring are referred to under the several generic
names of “bioindicators,” “bioaccumulative indicators,” “biomonitors,” and “sentinel
organisms,” and that these names are generally badly used. As often defined today, sen-
tinel species may be considered as any species providing a warning of a dysfunction or
an imbalance of the environment, or, more restrictively, a warning of the dangers of sub-
stances to human health. In the widest acceptance of the term, the sentinel species can be
( F i g u r e 7.1) :
• A bioindicator species, providing information by its absence (or presence) and/or
of abundance of individuals
• A bioaccumulative species, the capacity of which to accumulate contaminants at
levels much higher than those in the environment, designates it as the material of
choice for the monitoring of the degree of contamination of the environment
• A species for which modiications of biological parameters at one or various levels
of organization (molecular, cellular, physiological, organism, or behavioral) are
used to estimate the risks associated with the presence of contaminants
So, the terms of bioindicators and bioaccumulators are often used as synonyms for sen-
tinel species. However, although the two terms are indeed associated with the same objec-
tive of using living organisms to inform us about the quality of the environment and its
consequences, there is a conceptual difference between them. To avoid problems resulting
from different understandings of their separate meanings, and to maintain the integrity of
their use, Dauvin et al. (2010) recommended a clear definition of the meaning of the terms
used. It is therefore the definition of a sentinel species as a species showing modifications
of biological parameters (indeed biomarkers) that is retained in this chapter.
The first sentinel species used were chosen on the criteria of convenience of easy collec-
tion, availability, ease of breeding in the laboratory, and good genetic stability, but without
ecological relevance. An example is the freshwater crustacean Daphnia pulex , widely used
to test the toxicity of effluents in the 1970s. Chapman et al. (1994) showed that the tests
carried out on the reproduction of this species showed it to be more sensitive to pollutants
than other species of daphnids. Nevertheless, D. pulex has been replaced little by little by
Daphnia magna or Ceriodaphnia dubia , both of which are easier to breed in the laboratory.
A second criterion often advanced to justify the choice of a species as a sentinel spe-
cies is its ease of collection in the field and subsequent manipulation in the laboratory.
Mussels (bivalve mollusks of the family Mytilidae) are typical examples, with moreover
a large power of bioaccumulation of pollutants that have caused them to be widely used
in biomonitoring programs of coastal zones such as “Mussel Watch” in the United States
and in the Netherlands or the “Réseau d'Observation de la Contamination Chimique” of
the marine environment (ROCCH) in France. Furthermore, the biology of mussels, as well
as their mechanisms of biotransformation, and the mechanisms of toxicity of xenobiotics, are