Origin of Energy Metabolism Impairments - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 280

Food
availability

Feeding
behavior

Feeding rate

Digestion
digestive enzymes

Chemical
stress

Chemical
stress

Energy assimilated

Energy balance
CEA-SfG

Growth
reproduction

Maintenance
tolerance

Metabolic energy
AEC - Reserves

FIGURE 11.1
Potential effects of chemical stresses on energy metabolism. (Modified from De Coen, W.M., Janssen, C.R.,
Hydrobiologia , 367, 199-209, 1998; Dedourge-Geffard, O. et al., Chemosphere , 77, 1569-1576, 2009.)

chemical contaminants often transported there for detoxification. Therefore, organs such
as the vertebrate liver or the invertebrate digestive gland or hepatopancreas constitute the
main sites of accumulation of contaminants, and in particular contaminant trace metals, in
aquatic animals. Given that the invertebrate digestive gland or hepatopancreas has a major
role in digestion as well as in the detoxification and subsequent storage of toxic elements or
compounds, it is interesting and relevant to improve our knowledge of the possible effect
of pollutants on the activity of the digestive enzymes secreted by these organs.
Furthermore, within the framework of an evaluation of the quality of an environment,
variations in enzymatic activities in organisms are often one of the first responses to
chemical stress; they thus represent useful points in the confirmation of any toxic effects
(Lagadic et al. 2000; Van der Oost et al. 2003) before later ones are perceptible at higher
biological levels of organization (e.g., cellular, tissue, physiological, whole individual).
Biomarkers related to energy metabolism are thus potentially very interesting prognostic
tools, bearing in mind the close relationship existing between the energy balance and the
health of individuals (Depledge and Fossi 1994; De Coen and Janssen 2003).

11.2 Food Availability and Quality in Polluted Media
Living organisms exhibit highly different sensitivities to chemical stress, particularly
when they belong to different taxa but also, in some cases, when they are relatively closely
related phylogenetically (Chapter 7). The presence of contaminants in the medium can
exert direct toxic effects on the most sensitive species, inducing sublethal or even lethal
effects, particularly in cases of acute accidental pollution events. In addition, indirect effects
occur in communities exposed to chemical stress, with interactions between resources and
consumers (Fleeger et al. 2003).
At the base of food webs, increased productivity or enhanced microorganism biomass
has frequently been observed as a consequence of enrichment with organic matter. Despite
the toxicity of some of their compounds, petroleum hydrocarbons represent a significant