The impact of short term exposure to freshwater on marine fouling non-native species in three Scottish marinas.

Artificial structures in marinas are especially favourable habitats for many marine invasive non-native species (NNS). Reducing establishment of non-native species in marinas may reduce spread by recreational vessels. Marinas with a nearby freshwater source have fewer NNS, suggesting freshwater may be a possible tool for controlling NNS spread. This study was conducted to see if freshwater could be used as an effective treatment to reduce colonisation of marine fouling non-native species on artificial structures in marinas. The effects of 1-hour freshwater immersion were tested on experimental biofouling communities in three Scottish marinas with differing salinity regimes. 8 week old communities developed on settlement panels suspended from floating pontoons from July – August 2016 were immersed in either freshwater or ambient seawater, before being returned to their initial position on pontoons. Recovery of biofouling communities was monitored over an 8-week period post-treatment. Salinity varied over the growth and recovery phase to differing extents in each marina, with freshwater input affecting salinity variability. Fouling communities from the marina with the most stable high salinity conditions displayed the largest change to freshwater immersion. Comparing response to treatment between native and non-native species allows us to see if freshwater immersion may be an appropriate biosecurity tool for use in marinas.