Sentinel Species - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 175

within Shelter Island Yacht Basin (California). They identified 48 taxa with annelid poly-
chaetes (16 families) and peracarid crustaceans (one class and three orders) as the domi-
nant groups (overall >77% of total). Among the polychaetes, there was a higher richness
at “low” Cu and reference sites, than at higher Cu sites (Figure 7.6a). Syllid polychaetes
were the dominant group overall, and syllids had an enhanced percentage contribution
in the “high” contaminated sites, whereas the percentage contributions of spionid, orbi-
niid, and capitellid polychaetes were lower at “high” Cu sites (Figure 7.6a). Among the
crustaceans, peracarids were the most affected when sediment Cu was high (Figure 7.6b);
the number of amphipods was reduced to only four species (with a dominance of two of
them, representing ≈93% of the total crustaceans) in these contaminated sites, whereas at
“low” Cu and reference sites, 10 species were present, in relatively equitable proportions
(Figure 7.6b).
7.2.2.2 Intraspecific Variability
7.2.2.2.1 Sensitive Stages of Organisms
The reproductive and young growth phases of organisms attract the attention of ecotoxi-
cologists who consider that they are the most sensitive stages, and therefore key to the
preservation of the species in the ecosystem. Pessoa et al. (2011) exposed early life stages of
tilapia Oreochromis niloticus at 9 days post-hatch in semistatic experiments to sublethal con-
centrations of the carbamate insecticide carbofuran (8.3-397 μg L -1 ). Their results showed
effects on cholinesterase activity and a suite of behavioral endpoints (vision, growth and
predator avoidance skills at environmentally significant concentrations, and effects on
swimming and prey capture only at relatively high concentrations) that are directly related
to important ecological mechanisms relevant for their survival, growth, and recruitment
to the adult population. In a synthesis on the use of embryos and larvae of mollusks in tox-
icity tests published in 1999, His et al. confirmed the hypothesis of the relative sensitivity
of early life stages, indicating, however, some considerable exceptions such as resistance to
cadmium or insecticides. In order to test the total toxicity of dredging materials, Alzieu et
al. (2003) considered bioassays of embryotoxicity in the oyster Crassostrea gigas or tests on
copepodites (juvenile stages) of the copepod crustacean Tigriopus brevicornis to be sensitive
and discriminating, but reported young sea bass or the nauplius larvae of brine shrimp
( Artemia ) to show low sensitivity. Other authors have also demonstrated that larvae or
young do not systematically always show the greatest sensitivities to pollutants. For exam-
ple, Lotufo and Fleeger (1997) exposed two species of meiobenthic copepods ( Schizopera
knabeni and Nitocra lacustris ) to phenanthrene, and observed that, whereas for the first spe-
cies the nauplius stage is effectively the most sensitive, for the second, it is the mature
females which present a higher sensitivity than all other stages. Stubblefield et al. (1999)
showed that for rainbow trout, Oncorhynchus mykiss , the young were approximately three
times less sensitive to the toxic effects of zinc and cadmium than the adults. Furthermore,
these authors indicated that the acclimatization of young rainbow trout to sublethal con-
centrations of cadmium increases their tolerance by a factor of 25, whereas this tolerance is
increased only by 4.8 for the adults. Moreover, as demonstrated by Kammenga and Riksen
(1996), the intensity of the response of a population to xenobiotics is not always determined
by the most sensitive biological stage. Indeed, exposing two species of nematodes to cop-
per, they showed that the population growth rate of the two species is reduced in a similar
manner, whereas one of these species shows a higher sensitivity for other life history traits
(juvenile survival, duration of the juvenile period and of the period of reproduction, and
the daily rate of reproduction).