Origin of Energy Metabolism Impairments - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 283

processes that helped these isopods to cope with chronic pollution in a terrestrial environ-
ment contaminated by mining activities. In contrast, isopods from a reference site were
unable to distinguish between normal food and metal-rich food, and then consumption
was similar for both. Food selection allows the reduction of toxic metal uptake and limits
the induction of defense processes and associated energy costs. In the gastropod mollusk
Helix engaddensis , the presence of Cd or Cu in the food induced decreases in feeding and
growth rates. Inhibition due to Cd was irreversible, indicating a toxic effect, whereas fast-
ing due to Cu was reversible, indicating that the gastropods were able to identify and avoid
contaminated food (Swaileh and Ezzughayyar 2000).
Neurotoxicants such as insecticides can cause a reduction of filtration rates as a conse-
quence of a loss of coordination as studied in zooplankton, particularly, Daphnia (Reynaldi
et al. 2006 and literature quoted therein; Barata et al. 2007). In the presence of metals (Cd,
Zn), feeding impairments in Daphnia may result from digestive poisoning resulting from
the release of metals initially associated with the ingested microalgal food at the low pH
level encountered in the digestive tract (Barata et al. 2002 and literature quoted therein).
Whatever the classes of contaminants and the mechanisms involved in their effects on
feeding, Daphnia suffer delayed growth and maturation, which could be at the origin of
effects at the population level. In the decapod crustacean Nephrops norvegicus , food detec-
tion and uptake were disturbed at environmentally realistic concentrations of manganese.
In the field, such Mn concentrations can last as long as weeks in relation to the hypoxia
that commonly occurs in the habitat of this species. (Reducing conditions promote the
presence of the relatively more soluble Mn 2+ ion.) In addition, low levels of oxygen can
directly affect N. norvegicus , obliging them to come out of their burrows and disturbing
their feeding. For benthic organisms such as N. norvegicus , toxic effects of Mn can worsen
the severe problems that hypoxia causes on a worldwide scale (Krång and Rosenqvist 2006
and literature cited therein).
In a freshwater predator, the leech Nephelopsis obscura , exposed to cadmium (5, 10, or
50 μg L -1 ), only the highest dose tested induced a decrease in food ingestion, whereas the
assimilation efficiency was unaffected by any of the tested doses. Despite reduced general
activity and respiration rate, the growth rate was lower in specimens originating from the
treatment with Cd at 50 μg L -1 , since the energy allocation was focused on mucus produc-
tion and the sustainability of reproduction (Wicklum and Davies 1996).
In nematodes, modeling based on the Dynamic Energy Budget theory (Chapter 12) has
been used to analyze the physiological modes of action of different toxicants (Alvarez et
al. 2005, 2006). In Acrobeloides nanus , exposure to pentachlorophenol and carbendazim
can induce a reduced energy uptake in the organism, and the same process can occur in
Caenorhabditis elegans exposed to Cd and carbendazim.
To assess sediment toxicity, the gastropod Hydrobia ulvae was exposed to a gradient of
estuarine sediments contaminated by mining activities (Shipp and Grant 2006). The feed-
ing rate was determined by counting fecal pellets, which provide a relevant indicator of
the quantity ingested during the hours preceding the assay. The highest production of
fecal pellets was observed in individuals collected from the control site, and it decreased
for individuals exposed to increasingly contaminated sediments. The production of fecal
pellets was positively correlated with growth (incremental size increase) of the gastropods
(Figure 11.3).
In fish, metal exposure can affect food uptake, but no general trend can be established.
For instance, exposure of the rainbow trout Oncorhynchus mykiss to Cu induced an increase
of appetite, suggesting a metabolic cost needing higher energy inputs, in agreement with
increased oxygen consumption during phases of intense swimming activity. A similar