Marine Ecosystems under Toxic Pressure - Vulnerability of Coastal Ecosystems and Adaptation - page 27

improved capacity to adapt to environmental stress [DEP 96,
HAU 03]. Numerous studies suggest that contamination can constitute
a strong selective pressure, susceptible to leading to adaptive changes
in the natural populations.
1.4.3. Host-parasite interactions
Parasites represent one of the most important natural biotic factors
of environmental stress on natural populations. They can modify the
physiology and metabolism of animals, and in consequence can
influence characteristics of the lifecycle such as survival, growth and
fecundity. Parasite infection can modify intra- and inter-species
competition for resources, by rendering the infected individuals less
competitive [REL 06].
Other stress factors, such as chemical products in the form of
heavy metals or organic compounds, can exacerbate the harmful
effects of infection. Conversely, a greater vulnerability of parasites to
contaminants can lead to a decrease in the rate of infection [BOO 05].
Eira et al . [EIR 09] indicated that infestations of cestodes in eels
( Anguilla anguilla ) can modify the metabolic/storing processes of
metals in the host's tissues and thus reduce the bodily charge in
chrome and nickel.
Numerous chemical compounds have a tendency to alter the
immune function of organisms, which is an animal's main system of
protection against infections [GAL 01, GAL 03]. Two types of effect
can be seen: first, the impact of pathogenic agents on animals present
in the polluted zones and second, the interactions between the
pesticides and biological combating agents [HOL 10]. Thus,
environmental contaminants and infectious diseases are considered to
be the main factors contributing to the global decline in amphibians
[FOR 06, KIE 02]. Eder et al . [EDE 07] have found evidence of a
significant infestation by the hematopoietic necrosis virus that infects
salmon ( Oncorhynchus tshawytscha ) following exposure to pesticides.
Several examples of evidence have also been found in fish
(contamination by PCB [DUF 00] or sea-dwelling mammals). The