Low frequency offshore wind farm noise affects natural planktonic communities during an in situ microcosm experiment in Norwegian coastal waters

Abstract The effects of anthropogenic underwater noise, such as operational noise from offshore wind farms (OWFs), on plankton are poorly understood. A significant challenge in assessing the impact of noise on natural communities is the lack of holistic and ecologically relevant experimental setups mimicking soundscapes and communities under close-to-natural conditions. To address this, we conducted a 22-hour bottle incubation experiment using real OWF recordings broadcast underwater, creating three distinct sound exposure levels: High Noise with an average sound pressure level of 106 dB re 1µPa, Medium Noise at 94 dB re 1µPa and the Control, only experiencing the ambient sound at 80 dB re 1µPa, (over 50–2400 Hz band). At the community level, changes in phytoplankton growth, zooplankton grazing, and oxygen concentrations were assessed across treatments. After a 22-hour exposure, phytoplankton growth rates were significantly higher under noise exposure. This was concurrent with a more positive net oxygen balance suggesting higher primary production when the community was exposed to OWF noise. However, grazing rates did not differ significantly among experimental conditions. This study implemented a new experimental methodology and demonstrated that short-term OWF noise exposure significantly impacts phytoplankton growth rate and oxygen balance, but not zooplankton in a coastal lagoon.