Anthropogenic noise influences on marine soundscape variability across coastal areas

Acoustic data was collected across 15 sites distributed through the coastal area of Rio de Janeiro, Brazil, encompassing regions of different natural characteristics. Noise levels and the acoustic complexity index were calculated. Quantity and composition of anthropogenic sound sources varied across recording sites, with at least one type of sound source being registered in each location. A cluster analysis using third-octave levels from eight frequency bands divided recording sites into two groups, one considered as impacted by anthropogenic noise and the other as less-impacted. The noisiest recording locations were those with higher numbers of anthropogenic sound sources, specifically large ships. It was evidenced that anthropogenic noise affects not only noise levels, but also low-frequency acoustic complexity, which decreased in the presence of vessel traffic. The constant noise input of human activities tended to mask natural variability in the soundscape at lower frequencies.