Abstract
Copper is essential for healthy cellular functioning, but this heavy metal quickly becomes toxic when supply exceeds demand. Marine sediments receive widespread and increasing levels of copper contamination from antifouling paints owing to the 2008 global ban of organotin-based products. The toxicity of copper will increase in the coming years as seawater pH decreases and temperature increases. We used a factorial mesocosm experiment to investigate how increasing sediment copper concentrations and the presence of a cosmopolitan bioturbating amphipod, Corophium volutator, affected a range of ecosystem functions in a soft sediment microbial community. The effects of copper on benthic nutrient release, bacterial biomass, microbial community structure and the isotopic composition of individual microbial membrane [phospholipid] fatty acids (PLFAs) all differed in the presence of C. volutator. Our data consistently demonstrate that copper contamination of global waterways will have pervasive effects on the metabolic functioning of benthic communities that cannot be predicted from copper concentrations alone; impacts will depend upon the resident macrofauna and their capacity for bioturbation. This finding poses a major challenge for those attempting to manage the impacts of copper contamination on ecosystem services, e.g. carbon and nutrient cycling, across different habitats. Our work also highlights the paucity of information on the processes that result in isotopic fractionation in natural marine microbial communities. We conclude that the assimilative capacity of benthic microbes will become progressively impaired as copper concentrations increase. These effects will, to an extent, be mitigated by the presence of bioturbating animals and possibly other processes that increase the influx of oxygenated seawater into the sediments. Our findings support the move towards an ecosystem approach for environmental management.
Highlights
Trace levels of copper are essential for the healthy functioning of organisms owing to its central role in a range of enzymes [1]
Bacterial biomass and all nutrient concentrations at the end of the 10-day experiment were affected by significant copper 6 C. volutator interactions (p#0.011 in all cases; Table 2; Figure 1b–e)
Bacterial biomass clearly declined in response to the copper additions, but remained higher in the presence of C. volutator at concentrations between 30 and 302 mg Cu [kg wet sediment]21 (Figure 1b)
Summary
Trace levels of copper are essential for the healthy functioning of organisms owing to its central role in a range of enzymes [1]. This heavy metal is well known for its toxicity and the biocidal properties of copper have been exploited by mankind for centuries. Cu2+ ions slowly leach from the paint and particulate copper is further released to the environment in flakes of paint produced during the periodic cleaning and maintenance of antifoulantcoated structures [2,4,5]. Low biological demands for copper and the typically reducing nature of marine sediments result in the accumulation of this element at the seabed [8], with concentrations in ship recycling zones, beneath fish farms and near boat yards reaching up to 703, 805 and 2230 mg Cu [kg dry sediment]21 respectively [9,10,11]
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