Marine reef soundscape monitoring with fiber-optic distributed acoustic sensing

Abstract

Coral reefs are essential marine ecosystems that support a vast array of biodiversity and provide numerous benefits, including fisheries, tourism, and coastal protection. However, these ecosystems are increasingly threatened by various factors, including anthropogenic noise from activities such as shipping and coastal development. Traditional acoustic methods of monitoring reef health, such as hydrophones, are limited by their point-based sensing, reliance on batteries, and need for manual data retrieval, which can be labor-intensive and costly. In this study, we explore the application of fiber-optic distributed acoustic sensing (DAS) for real-time marine reef monitoring, a new application compared to its previous use in deep-sea soundscape monitoring. We deployed a fiber-optic DAS system in a reef area on the coast of the Central Red Sea, alongside a conventional hydrophone for comparison. The experiment was conducted in a degraded inshore reef near the KAUST shoreline, characterized by sand, macroalgae, scattered boulders, and encrusting sponges. This site was selected as a proxy for coral reef monitoring due to its biological activity, including snapping shrimp and the presence of reef-related fish species. Our observations revealed significant acoustic activity within the 1.5 to 5 kHz range, with snapping shrimp sounds increasing after the onshore lights were switched off, consistent with known behavioral patterns of increased acoustic activity during low-light conditions. Additionally, we detected various fish vocalizations, including drums and impulses, within the 100 to 1000 Hz range. The DAS system also successfully tracked the timing and trajectory of scuba diver movements along the reef. These findings demonstrate the potential of fiber-optic DAS technology to provide high-resolution spatial mapping of reef soundscapes, offering a comprehensive and cost-effective solution for continuous reef monitoring, thereby demonstrating the feasibility of DAS for real-time acoustic monitoring in reef environments.