Marine Ecosystems under Toxic Pressure - Vulnerability of Coastal Ecosystems and Adaptation - page 25

green algae. Although herbicide has direct toxicity for green algae, the
nutrients released by the decomposition of macrophytes also benefited
algae [SLI 05].
1.4.2. Contamination and impact on genetic diversity
The main genetic impacts reported in the context of contamination
studies on populations include:
- increases in mutation rates;
- changes in the whole genome of genetic diversity due to
demographic bottlenecks;
- changes in alleles or genotypic frequencies caused by selection
triggered by contaminants;
- changes in the dispersion methods of gene fluxes that modify the
genetic relationship between populations [BIC 11].
Evidence of the direct effects of pollution on genomes has been
found in land organisms and in particular in the case of contamination
by radionuclides [DUB 96] and aromatic polycyclic compounds
[SOM 02, YAU 00].
The indirect effects of pollutants on genomes can result from a
massive reduction in the size of the population resulting from
mortality or even the selection of alleles or genotypes associated with
“tolerance” in the contaminated zones and elimination of the majority
of “sensitive” genotypes.
Only a few studies have found evidence for the existence of
genetic erosion due to a massive reduction in population size in the
contaminated sites. For example, Demarais et al. [DEM 93] concluded
that the modifications in the genetic structure of freshwater fish
populations (Gila de seminuda), observed after acute accidental
exposure to rotenone (insecticide), were probably due to a genetic
bottleneck caused by an elevated mortality rate. Murdoch and Hebert
[MUR 94] put forward the same hypothesis to explain the