Separate and combined effects of copper and freshwater on the biodiversity and functioning of fouling assemblages

- For the first three months, no effects of copper or freshwater were found.
- After three months, copper reduced community attributes and ecosystem functioning.
- Water flow, fresh and saline, reduced community respiration.
- No interactive effect was detected between copper and freshwater.

Increased levels of anthropogenic stressors in the marine environment are leading to complex changes in its diversity and functioning. Many marine ecosystems are exposed simultaneously to multiple stressors, and their combined effects are difficult to predict. Climate change will intensify the input of terrestrial pollutants and increase the flow of water to coastal systems through increased precipitation. Subtidal assemblages were subjected to factorial combinations of copper and freshwater to test effects on their structure and on ecosystem processes. Assemblages were also subjected to seawater to separate the intended effects of water flow and salinity. For the first three months, no effects of copper or freshwater were found. After three months, copper significantly reduced the taxon richness and the percentage cover of taxa, and reduced the rate of community respiration and gross primary production. The flow of water also reduced community respiration, regardless of whether the water was fresh or saline.