Biology Reference
In-Depth Information
2002). Based on the bioaccumulative capacities of the mussels, this network required the
implementation of transplants because of the relatively low availability of local mussels
to provide cover along all the French Mediterranean Coast, and because no local closely
related species fulfilled enough of the necessary criteria to be chosen as a replacement.
The use of transplants can only be envisaged if the conditions of the environment allow
the species to acclimatize. Conversely, this technique can be also used to try to explain the
causes of the absence of a species in an environment, the ecological conditions of which
seem nevertheless to be adequate to meet its requirements, or to eliminate some hypoth-
eses on such absences. An example is that of the mussel Mytilus edulis , absent from the
Gironde estuary (with the exception of its mouth), whereas oysters ( Crassostrea gigas ) are
widely present, although abiotic factors are nevertheless apparently favorable. By trans-
plantations, Geffard et al. (2004) showed that the metal contamination of the estuary could
not be the cause of this absence, the transplanted mussels developing there as well as oys-
ters, with effective mechanisms of metal detoxification and without deleterious effects on
their condition indices.
7.1.3.2 Implementation of Biomonitoring
7.1.3.2.1 Risk of Invasive Species
For commercial (furs, food products, etc.) and decorative purposes (stretch of water), in
leisure activities (ornamental fish keeping, hunts, fishing) or as subjects of study, man has
voluntarily introduced into his environment species that do not usually live there. Few
of those succeed in prospering in this new environment, but those that do succeed can
be the cause of real ecological disasters. By definition, transplanted sentinel species are
able to acclimatize in their new environment, and thus to colonize it. Before deciding to
introduce nonnative species in any ABM program, it is thus important to think about the
consequences. So, in the example presented above (Geffard et al. 2004), the transplantation
of mussels into the Gironde estuary appears to have been without consequences, because
the mussels naturally have the opportunity of settling there, but do not so.
7.1.3.2.2 Life History
An important factor to be taken into account in the use of sentinel species is the exposure
history of the transplanted individuals. In this respect, it is important to pay attention to
the history of exposure to pollutants, but also to natural ecological parameters such as
bathymetric level on the subtidal zone.
It has been well established for several decades that, within the same species, popula-
tions previously exposed to anthropogenic compounds are able to cope with pollutants
more efficiently than “naive” individuals. Takamura et al. (1989) compared the responses
of 118 strains of benthic cyanophyceae and eukaryotic algae, from rivers that are unpol-
luted or polluted by mining activities (Cu and Zn), on exposure to Cu by measuring their
photosynthetic activity (Table 7.1). They showed that the exposure concentration of Cu that
caused 50% inhibition of photosynthesis (IC 50 ) was positively correlated with the Cu con-
centrations in the river from which the algae had been isolated.
Berthet et al. (1992) showed that for identical contaminations with silver, carried out
at the same season but with animals of different origins, oysters Crassostrea gigas of the
same size and at the same stage of sexual maturity, could accumulate the metal in quanti-
ties varying by one order of magnitude. Furthermore, bioaccumulation at different levels
was associated with different fractionations of silver between the cytosolic and particulate
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