Habitat-mediated noise pollution reduction in seagrass meadows

Abstract

Despite widespread effects of anthropogenic noise on marine organisms, it is still unclear how the propagation of noise is influenced by habitat degradation. Here, we used field experiments to evaluate habitat-mediated reduction of noise pollution. We conducted habitat characterizations, faunal surveys, and transmission loss measurements at sites in subtropical and tropical seagrass ecosystems, across a range of habitat conditions. We found that recreational boat noise was reduced more at sites with denser habitats. For example, in Belize, a site with almost total coverage of seagrasses and attached macroalgae attenuated noise ~4 dB re 1 μPa more (reducing acoustic energy by ~37 %) over 5 m compared to a site with little habitat structure. Other factors that influenced transmission loss included water depth, dissolved oxygen, and temperature. Neither habitat density, nor any of the other environmental variables that affected transmission loss, influenced the abundance, richness, and composition of seagrass-associated faunal communities. The rich faunal communities found in sparser habitats could thus be disproportionately affected by the increased noise pollution exposure. Our work provides empirical evidence that seagrass habitats play a role in attenuating noise pollution, leading to greater protection for faunal communities and the seagrasses themselves. These findings strengthen our understanding of coastal soundscape-habitat interactions and demonstrate that the ability of seagrasses to dampen noise is a valuable ecosystem function that has so far largely been undervalued.

Keywords: Acoustic attenuation; Belize; Florida; Recreational boat; Thalassia testudinum; Transmission loss.