Effects of a desalination outfall on marine invertebrate recruitment: impacts and recovery

Desalination plants are becoming increasingly common worldwide, but their ecological impacts are poorly understood. Many desalination plants draw in large volumes of seawater, extract salt to obtain freshwater, then pump... [ view full abstract ]

Desalination plants are becoming increasingly common worldwide, but their ecological impacts are poorly understood. Many desalination plants draw in large volumes of seawater, extract salt to obtain freshwater, then pump hypersaline effluent containing excess salt out to sea. There are numerous impact pathways through which the effluent might affect marine biota, including salinity toxicity, change in other water quality parameters (e.g. pH), contaminants, change in hydrodynamics, and indirect effects. Here we report a 6-year study testing for impacts of a desalination outfall on the recruitment of offshore marine invertebrates, and subsequent recovery from impacts. We measured both recruitment and salinity in a multiple-before-after-control-impact (MBACI) design, sampling at replicate times and locations before, during, and after plant operation. Within this we also conducted a predator exclusion study to separate direct effects of the effluent from indirect predator-mediated effects. This study provides a powerful test for impacts at various distances from the outfall, and offers rare insight into the impact pathways of a growing form of human disturbance.