Sentinel Species - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 168

the particular contaminants at a given site important in determining which organisms are
more susceptible than others? Although they provide elements of answers to some of these
questions, Weis et al. (2011) call for further work to confirm or generalize their results.
7.2.1.2 Roles in Biogeochemical Cycles
7.2.1.2.1 Bioturbation of Sediment and Transformation of Organic Matter
Within the sedimentary compartment, certain species such as the annelid N. diversicolor
(Figure 3.7a), by their activities of bioturbation, play a key role in the transfer of pollutants,
or nutrients, between the sediment and the overlying aqueous phase (Mermillod-Blondin
et al. 2005; Banta and Andersen 2003). By excavating burrows in the sediment, the worms
increase the surface area of exchange between sediment and the water; they move organic
and mineral material including various pollutants, modifying their distribution and pro-
moting their homogenous distribution in the sediment column; and they contribute to
the oxygenation of the sediment close to the burrows. Furthermore, because they usually
feed on detrital organic matter on the surface of sediments, N. diversicolor significantly
influence the speed of decomposition of organic matter in the estuarine ecosystem, and
any disturbances of their activities will have a direct repercussion on this decomposition
rate (Moreira et al. 2006). By their action of oxygenation of the sediment, endobenthic poly-
chaetes such as N. diversicolor or Arenicola marina also stimulate the local aerobic micro-
flora and so strengthen their impact on the processes of organic matter degradation and
biotransformation of xenobiotics (Banta and Andersen 2003). Timmermann et al. (2011)
studied the effects of bioturbation by the common lugworm A. marina on the fate of oil
hydrocarbons (alkanes and polycyclic aromatic hydrocarbons) in situ during a simulated
oil spill in a shallow coastal area in a fjord in Denmark. They observed stimulation of both
physical removal and microbial degradation of oil compounds in deeper sediments layers
by A. marina , whereas the fate of oil compounds deposited in surface layers was affected
by other bioturbating infauna such as N. diversicolor , Corophium volutator , and Hydrobia spp.
Studying the release of a polychlorobiphenyl (PCB) ([ 14 C]PCB 32) from Baltic Sea sediment
to water, Hedman et al. (2009) indicate that biological reworking of the sediment by the
amphipod Monoporeia affinis (a particle biodiffuser) or the polychaete Marenzelleria sp.
(a bioirrigator) can be just as, or even more, important than physical resuspension for the
remobilization of sediment-bound contaminants.
In freshwater ecosystems, various species contribute to the decomposition of leaves
including the crustaceans Gammarus pulex and Asellus aquaticus , and larvae of insects.
Their feeding is a major rate-limiting step in the processing of stream detritus. Thus, these
detritivores have a crucial role in the biogeochemical cycle of organic matter, and if they
are impacted by pollutants in their environment, this function is no longer performed or at
least is reduced (Maltby et al. 2002; Kunz et al. 2010 and literature cited).
7.2.1.2.2 Role of Primary Producers in Biogeochemical Cycle of Xenobiotics
Pigeot (2001) studied the role of various benthic communities (88 species or communities) on
the fate of certain metals (Cd, Cu, Pb, and Zn) in a coastal ecosystem, the Marennes-Oléron
basin, Fr. He observed that the benthos stores, on average, 8 kg cadmium, 65 kg lead, 450
kg copper, and 6 tons zinc. Although oysters store the majority of cadmium (47.9%), copper
(89.3%), and zinc (94.5%), it is the primary producers (microphytobenthos + dwarf eelgrass,
Zostera noltii + sea purslane, Atriplex portulacoides ) which immobilize the great majority
of lead (90.3%), while playing a significant role in the storage of the three other elements
(Figure 7.4a-d). These primary producers, in particular the microphytobenthos, thus