Giant Kelp Forests Act as Natural Barriers to Motorboat Noise

Abstract

The world’s coastal areas are threatened by a variety of pollutants, including anthropogenic noise. To mitigate adverse effects of noise pollution on marine life, artificial bubble curtains are used in industrial contexts, such as offshore construction, to reduce noise propagation. In this study, we evaluate whether the giant kelp Macrocystis pyrifera, which possesses airbladders that aid flotation, effectively attenuates motorboat noise and could act as a natural sound barrier. We use hydrophones to compare motorboat noise attenuation along 60 m transects in a M. pyrifera forest and an adjacent control area without kelp in Algarrobo, central Chile. We found a significant reduction in the sound pressure level (SPL) of motorboat noise within the kelp forest, with a 6.1 dB difference at 60 m distance from the boat's passage compared to the control area. Motorboat noise was attenuated by M. pyrifera from 0.19 kHz to the maximum frequency measured (24 kHz). The peak frequencies of the motorboat noise signal in both areas (0.05–5 kHz), overlapped with the sensitivity frequency range of fish invertebrates and marine mammals, such as sea lions. Our results show, for the first time, the role of M. pyrifera in attenuating motorboat noise. Thus, highlighting an unexpected ecosystem function of kelp that may contribute to creating quieter environments for species associated with them, thus offering a nature-based solution to manage motorboat noise in temperate coastal areas.

Keywords: motorboat noise, sound pollution, giant kelp, noise attenuation, nature-based solution, bubble acoustics.