Conclusions: Biomarkers in Environmental Risk Assessment - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 420

contaminated sites have shown that effects observed experimentally on individual organ-
isms do not necessarily imply that measurable or ecologically significant effects on wild
populations of fish will occur at the same or similar exposure levels, as documented in
the Hudson River for striped bass Morone saxatilis and white perch Morone americana
(Barnthouse et al. 2003, 2009). Physiological acclimation or genetic adaptation in popula-
tions chronically exposed to contaminants in their medium is one of the possible explana-
tions (Amiard-Triquet et al. 2011), but ecological processes involving interactions between
tolerant and sensitive species may be another part of the story (Figure 3.2).
16.3.1 Biomarkers of Ecological Relevance
Individual responses to chemical stress such as physiological and behavioral impairments
or life history traits are ecologically relevant since survival, growth, and reproduction are
fundamental to organism fitness (Figure 16.1). In addition, they can be also linked to infra-
individual biomarkers as exemplified by Xuereb et al. (2009b) for AChE inhibition and
behavioral alteration, or for endocrine disrupting chemicals (Figure 8.5).
There are no clear links from induction of defenses to individual health or reproduction.
These mechanisms help an organism to cope with the presence of hazardous compounds
in the environment. This situation is well documented in areas where organisms chroni-
cally exposed to contaminants in their environment have become tolerant, allowing them
to survive and reproduce (Chapters 3 and 14). It is only when defenses are overwhelmed
that damage can occur even if indirect effects, namely, the cost of tolerance, can negatively
affect population dynamics, biomass, and densities (Chapter 12). Certain mechanisms
of defense can turn out to be less protective than initially expected, such as the produc-
tion of reactive metabolites resulting from xenobiotic biotransformation by phase I and
II enzymes (Chapter 3). However, biomarkers of ecological relevance must be preferably
searched for among biomarkers of damage.
The ecological significance of oxidative stress—which occurs when the rate of production
of reactive oxygen species (ROS) exceeds the capacity of the antioxidant defense and repair
mechanisms leading to oxidative damage to biological macromolecules—has recently gen-
erated an abundant literature, with a special issue of Functional Ecology (vol. 24) devoted to
The Ecology of Antioxidants and Oxidative Stress in Animals in 2010, whereas a whole topic was
edited by Abele et al. (2012) on Oxidative Stress in Aquatic Ecosystems with several chapters
devoted to marine animal models for aging, development, and disease. Mammalian and
avian studies have provided evidence that oxidative stress has an important physiological
cost, affecting longevity, reproduction, immune responses, and intense physical activity
(Costantini et al. 2010). Whether and how increased ROS impinges on fitness in the wild
is a judgment difficult to make. The gaps in our knowledge are larger when considering
fish, and even more in the case of invertebrates. The latter are generally characterized by
low metabolic rates and ROS formation, associated with lower antioxidant enzyme activi-
ties compared to vertebrates (Buttemer et al. 2010). In aquatic organisms, Pašková et al.
(2011) report that only few experimental studies with pesticides have directly linked devel-
opmental toxicity with key oxidative stress endpoints, such as lipid peroxidation, oxida-
tive DNA damage, or modulation of antioxidant mechanisms, but they also mention that
pesticide-related oxidative damage occurs in exposed adult fish, amphibians, and inverte-
brates. They conclude that the available experimental data provide support to the concept
that oxidative stress is a highly important mechanism in pesticide-induced reproductive
or developmental toxicity, and that other stressors may also act by oxidative mechanisms.
Maintaining and up-regulating antioxidant defenses and repair of the damaged molecules