For instance, algae spiked with metals have been used to demonstrate trophic
transfers of a variety of metals to bivalves or crustaceans (Croteau et al. 2005;
Goulet et al. 2007; Komjarova and Blust 2009). Experimental studies can more
precisely gauge contaminant fates by spiking with labeled contaminants. Radioisotopes of metals have been used to label food sources and thus trace species-specific
bioaccumulation dynamics by monitoring the radioactivity in consumers after pulsechase feeding (Conley et al. 2009; Golding et al. 2013). Food-resource enrichment
by stable isotopes of metals makes an interesting alternative approach to determine
the relative contributions of food and water to metal contamination in grazers
(Komjarova and Blust 2009). Indeed, isotopic ratio measurements can be used in
microcosm experiments to characterize and model the physiological mechanisms
involved in the assimilation of metals by the consumers from the biofilm they
ingested (Croteau et al. 2005). To our knowledge, the trophic transfer of organic
contaminants from biofilms to higher-level organisms has not yet been studied in
microcosm experiments.
Microcosm experiments do provide accurate information on the dietary dynamics
of contaminants in simplified food chains, but they are often specific to a prey/
consumer pair, and consequently only partially reflect the environmental complexity
governing trophic transfers (e.g., multiple food sources, biofilm structure, nutrient
loads, and more). In addition, the choice of the microorganism(s) used as a contaminated food source and the spiking method remain challenging tasks. Indeed, metals
assimilation by consumers has been reported to be closely related to microbial
species and their respective ability to bioaccumulate metals, to metal distribution
in the microbial cells, and obviously to community structure (Goulet et al. 2007;
Conley et al. 2009; Komjarova and Blust 2009; Golding et al. 2013). On one hand,
the influence of community complexity is omitted when monospecific biofilms are
used as a food source. On the other hand, the acclimatization and exposure of a fieldcollected biofilm to laboratory conditions are likely to provoke structural and
morphological changes in this complex food source (Fechner et al. 2011; BarralFraga et al. 2016). In most food web experiments, microbial biofilms are contaminated prior to introduction in the microcosm (e.g., Conley et al. 2009; Komjarova
and Blust 2009; Xie et al. 2010; Kim et al. 2012; Li et al. 2012; Perrier et al. 2018;
Hudson et al. 2019); nevertheless a few studies, usually in complex mesocosms,
have also investigated the effect on trophic transfer of concomitant contamination of
food resource and media, thus mimicking field conditions (e.g., Pinder et al. 2011;
Cleveland et al. 2012; Kim et al. 2016; Friesen et al. 2017; Park et al. 2018).
One way to go beyond the limitations of microcosm experiments is to follow
contaminant fate directly in the field. Indeed, various studies have investigated the
bioaccumulation of metals or organic compounds in natural environments by
collecting a variety of organisms including – but not limited to – microbial biofilms
(Croteau et al. 2005; Vinot and Pihan 2005; Walters et al. 2008, 2015; Coat et al.
2011; Jardine et al. 2013; Ruhí et al. 2016). Understanding trophic enrichment with a
contaminant in the field first requires an accurate description of local food web
structures. Hence, stable carbon and nitrogen isotopes in biological tissues
and microbial biofilms are usually analyzed (Croteau et al. 2005; Walters et al.
Role of Biofilms in Contaminant Bioaccumulation and Trophic Transfer in Aquatic. . .
137
transfers of a variety of metals to bivalves or crustaceans (Croteau et al. 2005;
Goulet et al. 2007; Komjarova and Blust 2009). Experimental studies can more
precisely gauge contaminant fates by spiking with labeled contaminants. Radioisotopes of metals have been used to label food sources and thus trace species-specific
bioaccumulation dynamics by monitoring the radioactivity in consumers after pulsechase feeding (Conley et al. 2009; Golding et al. 2013). Food-resource enrichment
by stable isotopes of metals makes an interesting alternative approach to determine
the relative contributions of food and water to metal contamination in grazers
(Komjarova and Blust 2009). Indeed, isotopic ratio measurements can be used in
microcosm experiments to characterize and model the physiological mechanisms
involved in the assimilation of metals by the consumers from the biofilm they
ingested (Croteau et al. 2005). To our knowledge, the trophic transfer of organic
contaminants from biofilms to higher-level organisms has not yet been studied in
microcosm experiments.
Microcosm experiments do provide accurate information on the dietary dynamics
of contaminants in simplified food chains, but they are often specific to a prey/
consumer pair, and consequently only partially reflect the environmental complexity
governing trophic transfers (e.g., multiple food sources, biofilm structure, nutrient
loads, and more). In addition, the choice of the microorganism(s) used as a contaminated food source and the spiking method remain challenging tasks. Indeed, metals
assimilation by consumers has been reported to be closely related to microbial
species and their respective ability to bioaccumulate metals, to metal distribution
in the microbial cells, and obviously to community structure (Goulet et al. 2007;
Conley et al. 2009; Komjarova and Blust 2009; Golding et al. 2013). On one hand,
the influence of community complexity is omitted when monospecific biofilms are
used as a food source. On the other hand, the acclimatization and exposure of a fieldcollected biofilm to laboratory conditions are likely to provoke structural and
morphological changes in this complex food source (Fechner et al. 2011; BarralFraga et al. 2016). In most food web experiments, microbial biofilms are contaminated prior to introduction in the microcosm (e.g., Conley et al. 2009; Komjarova
and Blust 2009; Xie et al. 2010; Kim et al. 2012; Li et al. 2012; Perrier et al. 2018;
Hudson et al. 2019); nevertheless a few studies, usually in complex mesocosms,
have also investigated the effect on trophic transfer of concomitant contamination of
food resource and media, thus mimicking field conditions (e.g., Pinder et al. 2011;
Cleveland et al. 2012; Kim et al. 2016; Friesen et al. 2017; Park et al. 2018).
One way to go beyond the limitations of microcosm experiments is to follow
contaminant fate directly in the field. Indeed, various studies have investigated the
bioaccumulation of metals or organic compounds in natural environments by
collecting a variety of organisms including – but not limited to – microbial biofilms
(Croteau et al. 2005; Vinot and Pihan 2005; Walters et al. 2008, 2015; Coat et al.
2011; Jardine et al. 2013; Ruhí et al. 2016). Understanding trophic enrichment with a
contaminant in the field first requires an accurate description of local food web
structures. Hence, stable carbon and nitrogen isotopes in biological tissues
and microbial biofilms are usually analyzed (Croteau et al. 2005; Walters et al.
Role of Biofilms in Contaminant Bioaccumulation and Trophic Transfer in Aquatic. . .
137