Soundscapes can diversify over time and space, with temporal variations being an important mechanism for understanding the ecological dynamics of an environment. Ecoacoustic indices are quantitative metrics used to characterize sound environments and have proven to be a crucial tool in soundscape ecology for estimating biodiversity and ecosystem processes. During the global COVID-19 pandemic, significant transformations occurred in soundscapes across various environments, including marine ecosystems, mainly due to the reduction of anthropogenic noise. We investigated temporal variations in an underwater soundscape in Baía da Ilha Grande, a protected area recognized as a hotspot for Brazilian marine biodiversity and a site of intense tourist activity. Using the global acoustic method, we applied ecoacoustic indices to sound data collected during two distinct periods: the first during the COVID-19 pandemic and the second in the post-pandemic period. We identified significant temporal changes in the soundscape when comparing the two collection periods. The results of the ecoacoustic indices indicate that, during the first collection period, the soundscape exhibited greater complexity and acoustic diversity compared to the second. We infer that the anthropause, resulting from the lockdowns imposed during the pandemic, reduced anthropogenic noise, allowing biological sounds to stand out and become the primary acoustic source in the environment during that period.