Development of photosynthetic biofilms affected by dissolved and sorbed copper in a eutrophic river

Abstract

Photosynthetic biofilms are capable of immobilizing important concentrations of metals, therefore reducing bioavailability to organisms. But also metal pollution is believed to produce changes in the microalgal species composition of biofilms. We investigated the changes undergone by natural photosynthetic biofilms from the River Meuse, The Netherlands, under chronic copper (Cu) exposure. The suspended particles in the river water had only a minor effect on reduction of sorption and toxicity of Cu to algae. Biofilms accumulated Cu proportionally to the added concentration, also at the highest concentration used (9 microM Cu). The physiognomy of the biofilms was affected through the growth of the chain-forming diatom Melosira varians, changing from long filaments to short tufts, although species composition was not affected by the Cu exposure. The Cu decreased phosphate uptake and algal biomass measured as chl a, which degraded exponentially in time. Photosynthetic activity was always less sensitive than algal biomass; the photon yield decreased linearly in time. The protective and insulating role of the biofilm, supported by ongoing autotrophic activity, was indicated as essential in resisting metal toxicity. We discuss the hypothesis that the toxic effects of Cu progress almost independently of the species composition, counteracting ongoing growth, and conclude that autotrophic biofilms act as vertical heterogeneous units. Effective feedback mechanisms and density dependence explain several discrepancies observed earlier.

Trophic transfer of metals along freshwater food webs: Evidence of cadmium biomagnification in nature

“…For example, topminnows (killifishes) that showed the highest Cu concentrations are known to feed opportunistically on biofilm at the water surface, whereas gobies that are the least contaminated species feed on benthic prey and bottom detritus. Because biofilms are huge reservoirs of organic biomass that can greatly accumulate contaminants (Barranguet et al 2002), feeding on water surface might explain why killifishes had the highest Cu concentration among fish. However, metal concentrations in sunfish varied greatly among species (Table 2), despite the fact that sunfish species shared similar feeding characteristics.…”

In situ spatio-temporal changes in pollution-induced community tolerance to zinc in autotrophic and heterotrophic biofilm communities

“…Genter et al (1987) noted a shift in phototrophic community composition from diatoms to cyanobacteria and green algae after exposure to Zn. Other studies also reported biofilm community shifts towards a dominance of cyanobacteria after long-term exposure to metals, indicating that cyanobacteria may be more tolerant to metal contamination (Barranguet et al 2002(Barranguet et al , 2003Serra et al 2009). Cyanobacteria are known to lack a xanthophyll cycle, but still contain significant amounts of zeaxanthin and other xanthophylls (Jeffrey and Vesk 1997), which could help explain their high tolerance to metals.…”

Analysis of Structural and Physiological Profiles To Assess the Effects of Cu on Biofilm Microbial Communities

“…These epilithic, epiphytic, or epipelon assemblages are generally described as biofilms (30). Barranguet et al, studying heavy metal effects on aquatic biofilms, showed that Cu affects the physiology of phototrophic organisms (1), that it accumulates in phototrophic biofilms proportionally to the concentration of exposure, and that some algal species react morphologically to an increased Cu concentration (3). However, the measured Cu effects on the photosystem were not related to changes occurring in the composition of the phototrophic community as observed by microscopy.…”

“…These authors did not detect large differences between bacterial communities growing at Cu concentrations ranging from 3 to 87 M. Our results suggest that the complex and organized structure of the biofilm (10,18,30) would not protect the bacterial community in the same way that sediments do, even through the formation of extracellular polymeric substances was found to increase several resistance capacities of each encased organism (24) by reducing the bioavailability of heavy metals (33). Short-and long-term toxicity tests of heavy metals on aquatic biofilms have focused either on the response of the phototrophic compartment (1,2,5,17) or on that of the heterotrophic compartment (34), but toxic effect assessments based on physiological tests (3,19) or studies considering the biofilm as a whole have not investigated the effect of Cu (6,23). Possible interactions between phototrophic and heterotrophic compartments of a biofilm may be disturbed when one compartment is severely affected by a stress factor, e.g., an increase in toxicant concentration.…”