Conclusions: Biomarkers in Environmental Risk Assessment - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 417

that the feeding rate exhibits different seasonal patterns in different bivalve species, the
mussel Mytilus edulis , the cockle Cerastoderma edule , and the Venus clam Chamelea gallina .
16.2.2 Active Biomonitoring
Active biomonitoring (Chapter 2) provides an opportunity for controlling biotic factors,
allowing the selection of standard organisms (homogeneous size, sex, reproductive status)
with similar previous histories (specimens produced by aquaculture or collected from a
reference site). Such experimental procedures are particularly applicable to filter-feeders
that access their food in the water column, especially bivalves, which are commonly used
for biomonitoring in Mussel Watch-type programs. However, it is important to know how
caging itself affects biological responses to chemical pollution, particularly through its
effects on food availability as discussed in Chapter 2, and also, in the case of fish, the effect
of caging densities (Oikari 2006). In cases where invertebrates have been caged, the ques-
tion of food availability has received a number of relevant responses such as the provision
of rocks covered with biofilm introduced into containers with the mudsnail Potamopyrgus
antipodarum (Gust et al. 2010), an ad libitum supply of alder leaves for amphipods Gammarus
fossarum (Forrow and Maltby 2000; Coulaud et al. 2011), or the presence of a significant
volume of sediment from the site of origin for polychaetes Arenicola marina (Ramos-Gómez
et al. 2011).
In addition, certain biomarkers can respond to stress associated with the transplantation
process (handling stress, anoxia, oxidative burst), as for total oxyradical scavenging capac-
ity responses in mussels Mytilus galloprovincialis (Camus et al. 2004). In fish, the induction
of plasma cortisol has been observed in response to general stress such as that encoun-
tered in handling and capture (Hontela 2000). In addition, stress induction during sam-
pling requires particular attention as it has been demonstrated to strongly affect immune
functions (Chapter 6).
Despite these limitations, caging has been widely used in recent years for biomonitor-
ing based on biomarkers determined in many species belonging to different taxa such as
gastropods (e.g., Gust et al. 2010), bivalves (Chapter 2), crustaceans (e.g., Lacaze et al. 2011a),
and fish (e.g., Brammell et al. 2010; Ji et al. 2010; Klobučar et al. 2010; Kerambrun et al. 2011).
16.2.3 Reference Site
As stated by Amiard-Triquet and Rainbow (2009), in our present state of knowledge, it is
unacceptable to study the ecotoxicological status of an aquatic medium without compari-
son against a reference site. Such a reference site must be chosen to be as close as possible
to the site under investigation, in terms of temperature, granulometry, organic content of
sediment, etc., in order to mitigate the importance of confounding factors. In freshwater
environments, an appropriate strategy is often based on an upstream/downstream proce-
dure. In estuarine areas, the reference site needs to be chosen to be as close as possible to the
first estuary in terms of salinity regime. In practice, it will probably be impossible to reach
perfect agreement between estuaries, but every attempt must be made to assess the effects
of any such differences where possible. Even this may prove impossible, for example, in
the case of differences in hydrodynamic conditions, but it remains necessary to make a
careful assessment of these differences. Even paired comparisons in freshwater environ-
ments between stations upstream/downstream from identified point-sources of pollution,
which are based on the assumption that physicochemical conditions are similar between
stations except for levels of bioavailable toxic compounds, are not totally satisfactory. The