Consequences of Energy Metabolism Impairments - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 315

In a freshwater invertebrate ( Nephelopsis obscura ), changes in energy allocation (i.e.,
increased mucus production) have been observed in animals exposed to cadmium under
laboratory conditions, thus contributing to a decreased growth rate compared with the
control animals (Wicklum and Davies 1996). Actually, the net available energy budget
for growth and reproduction may be considered a biomarker of the general condition of
health. An interesting and convenient application of this principle is the energy allocation
to growth and reproduction, that is, SfG. The SfG notably takes into account the assimila-
tion of energy through food, the energy released in respiration and lost in excretion—and
more particularly, nitrogen derivatives (Le Gal et al. 1997).
In fact, the SfG has been used for a long time to measure the impact of contaminants on
biological organisms in their natural habitat (Smaal and Widdows 1994). Such a method
is largely used in mussels, because of the extensive knowledge of their characteristics and
behavior, and their use as sentinel species in numerous biomonitoring programs (Smaal
and Widdows 1994; Widdows et al. 1997, 2002). Significant negative correlations between
PCBs, DDT, and organochlorine concentrations have been measured in tissues of exposed
mussels in the Venice lagoon, but not in the case of metals (Widdows et al. 1997). Some
surveys have shown that the significant decreases in SfG are essentially attributable to the
presence of PAHs (Widdows et al. 2002), or low values of SfG were attributed to exposure
to organotins and PAHs (Halldórsson et al. 2005).
Besides the use of SfG in environmental monitoring, variations of SfG are also stud-
ied under laboratory experiments. In the laboratory, Baillieul et al. (2005) investigated the
influence of food availability and cadmium exposure on daphnids' growth and reproduc-
tion. Both types of stress affected the body size of daphnids. The SfG was determined after
14 days of exposure and calculated either per individual or weight corrected. Decreasing
body weight was associated with decreasing SfG, regardless of whether SfG was calcu-
lated on individual basis or weight corrected. Instead, reproduction was positively cor-
related with SfG calculated on individual basis and negatively with SfG weight corrected.
Verslycke et al. (2004) studied the responses of N. integer in terms of SfG and CEA fol-
lowing exposure to the active substance chlorpyrifos. The treated groups were exposed—
under laboratory conditions—to environmentally relevant test concentrations of 0.038,
0.056, 0.072, and 0.100 μg L -1 during 48, 96, and 168 h. Under the conditions of experiments,
chlorpyrifos exposure significantly decreases SfG of N. integer , the effect being much
stronger at the highest test concentration of chlorpyrifos. Comparison of SfG versus CEA
allows the authors to conclude that the CEA would be a more sensitive biomarker than
SfG. Numerous factors have an impact on the SfG: temperature, dissolved oxygen con-
centration, food availability, sizes/weights of organisms, reproductive cycle (Mayer et al.
2002). Natural factors can also act as stressors and affect SfG. In the estuarine Atrina maura
(a bivalve mollusk), SfG was significantly correlated with food availability, i.e., microalgae
(Arrieche et al. 2011). Respiration measurement has proved to be integrative of metabolism
since it is characteristic of the intensity of the physiological processes at the time of mea-
surement. Increases in the standard metabolic rate (SMR) assessed through the measure-
ment of oxygen consumption were observed in various species (crustaceans, amphibians,
reptiles) exposed to metals in the field or under laboratory conditions (Rowe 1998; Hopkins
et al. 1999). In oysters ( Crassostrea virginica ) exposed to cadmium (50 μg L -1 ) under labo-
ratory conditions and acclimatized to various temperatures (20, 24, and 28°C), increases
in SMR were higher at 20°C, intermediate at 24°C, and lacking at 28°C, in comparison
with the control groups. Therefore, the efficiency of oxygen supply mechanisms could be
cancelled by the combination of high temperatures and exposure to cadmium (Lannig
et al. 2006). At cell level, significant respiratory costs were highlighted in rainbow trout