Marine Ecosystems under Toxic Pressure - Vulnerability of Coastal Ecosystems and Adaptation - page 30

associated with environments with an elevated level of stress were more
tolerant than those from stable environments. The hypothesis put
forward is that communities in disrupted natural habitats are preadapted
to disturbances and effectively more resistant to anthropogenic stress
factors [KIF 96]. However, it has been established that the effects of
multiple disturbances are not necessarily cumulative [PAI 98];
consequently, the superposition of disturbances in an ecosystem already
subject to chemical stress can trigger unexpected reactions from an
ecological point of view [BEL 04, SCH 01].
Resistance to contaminants has been identified in numerous taxa,
from microorganisms to vertebrates and vegetation [AMI 11, FEC 14]
and results from two processes: (1) a physiological acclimatizing by
individuals and/or (2) evolutionary adaptation in a population where
the contaminants can be considered as selective factors. However,
manifestations of resistance (adaptive responses) in populations
exposed to complex mixes of pollutants, in fresh water or seawater,
are still rare in the literature.
Individuals living in contaminated systems can produce
descendants (generation F1 and F2) who display a resistance to
pollutants similar to that observed for their parents; thus, this tolerance
can be considered as a genetic adaptation of the population [BEL 01,
JOH 11]. By using this approach, [KLE 01] have studied the
Cyprinodon fish's potential resistance to chemical stress in
experimental conditions. They underlined a decrease in the heritability
of resistance to chemical stress with the increasing number of
pollutants in the mixture. First, artificial selection carried out in a
laboratory on another fish ( Heterandria formosa ) showed a rapid
response to selection following exposure to cadmium; after a single
generation, a proportion of two selected lines of descent out of three
displayed an increase in resistance to cadmium [XIE 04]. Several
studies have highlighted the fact that populations of flounder
( P . flesus ) in three chronically polluted estuary systems in the United
States are resistant to aromatic hydrocarbons in their environment,
compared to fish in the region of habitats little impacted by HAP.
Resistance in the first generation, and sometimes in the embryos of
second generation, suggests that differential survival can be due to