Juan Carlos Azofeifa-Solano ^1,2* Christine Erbe ¹ Cristina DS Tollefsen ¹ Robert McCauley ¹ Rohan M Brooker ² Daniel Pygas ² Miles James Parsons ²

• ¹ Centre for Marine Science and Technology, Curtin University, Perth, Western Australia, Australia
• ² Australian Institute of Marine Science (AIMS), Crawley, Western Australia, Australia

Acoustic monitoring and soundscape analyses can provide data that supports the conservation and restoration of underwater habitats. However, the ecological relevance of sampling methodologies needs to be validated, and any potential biases quantified and minimized, before broad-scale implementation and use in management is viable. Here we tested how the distance and orientation of an acoustic sensor relative to a target habitat affects the received soundscape using a spatial array of hydrophones at different distances (1 m, 2 m, 5 m) and orientations (vertical vs horizontal) from a shallow coral reef. Hydrophones pointing towards the reef (horizontal) displayed an expected sound loss with increasing distance from the source. In contrast, hydrophones pointing upwards (vertical) had lower sound pressure levels when located closer to the source, and higher sound pressure levels when located further away. Considering biological and sound propagation effects, we conclude that sensor directivity influences the received soundscape, introducing a potential source of methodological bias within and across acoustic datasets. Our results have significant implications for the implementation of acoustic sampling in coastal habitats. The beam patterns of the sensors must be considered in the experimental design of acoustic data collection to reduce potential methodological biases.