Origin of Energy Metabolism Impairments - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 281

source of organic matter that can lead to a stimulation of bacterial microflora, favoring
bacteria-consuming species. Similarly, pulp mill effluents can stimulate the growth of dia-
toms. On the other hand, herbicides are responsible for a selective decrease of primary
producers, thus leading to a reduction in the abundance of their consumers as a conse-
quence of limited food availability (Fleeger et al. 2003 and literature quoted therein). In
this way, feeding would have an important role in the survival and physiological condi-
tion of Daphnia (freshwater cladoceran crustaceans), and, in the presence of the herbicide
molinate, changes in the quantity/quality of phytoplankton on which they feed could be
responsible for effects observed on their reproduction (Sánchez et al. 2004 and literature
quoted therein).
At higher levels in the food web, interactions grow increasingly complex (Figure 3.2);
nevertheless, it is clear that the tolerance of some populations/species to chemicals does
not guarantee their durability if their major prey species are sensitive, thus reducing food
and therefore energy available from their medium. For instance, a decline in recruitment
of several littoral bivalve species in British estuaries strongly impacted by the use of tri-
butyltin, would have influenced the distribution of certain wading bird species (Bryan
and Gibbs 1991). In a lake impacted by mining activities, growth, fecundity, and lipid con-
centrations were impaired in the fish Catostomus commersoni , despite Cu and Zn tissue
concentrations remaining within maintained limits of metal homeostasis. On the other
hand, it was evident that—as a consequence of decreased diversity and density of mac-
roinvertebrates—fish from this metal-rich lake invested much more energy in foraging
(Munkittrick et al. 1991).
Considering not only two successive links of the trophic chain but the whole system,
a review by Hanazato (2001) dealing with freshwater pelagic organisms, has shown that
low pesticide concentrations directly damaging only relatively large taxa (e.g., Daphnia )
may affect the population dynamics of smaller zooplankton species, particularly rotifers,
indirectly through competitive relationships. The final consequence was an elongation of
the food chain and a reduction of energy transfer efficiency from primary producers to
top predators since each transfer from one level to the next corresponds to an energy loss.
In natural media subjected to pollutant inputs, decreased food availability or increased
competition can limit the ability of a given species to maximize its energy uptake, thus
leading to the consumption of unusual food and to reduced energy conversion (Morrow
et al. 2004 and literature quoted therein). In mammals and fish, it has been reported
that not only food quantity but also its quality could influence detoxification ability and
stress. Fasting has no clear effects on general stress parameters (cortisol or glucose con-
centrations), whereas effects on biotransformation are more obvious, indicating generally
a decrease of different enzyme activities in the liver (Morrow et al. 2004 and literature
quoted therein).
In addition, food quality can interfere with energy metabolism through its degree of
contamination. An impairment of lipid metabolism and storage was observed in the
aquatic bird Cairina moschata , the Muscovy duck, exposed to dietary Cd (Lucia et al.
2010). When rainbow trout Oncorhynchus mykiss were fed oligochaete worms Lumbriculus
variegatus , previously exposed to metal-rich sediments, the instantaneous growth rate
became more and more reduced with increasing contamination of food (Figure 11.2,
experimental groups A to E). According to Hansen et al. (2004), growth inhibition would
be mainly a result of the reduction of food conversion efficiency in biomass rather
than of a decrease in food uptake, which was limited in this study contrary to other
observations.