Acoustic enrichment trials using autonomous cameras on a Hawaiian coral reef

Playbacks of ambient sound from healthy shallow coral reefs, known as acoustic enrichment (AE), can attract fish larvae and potentially coral larvae to degraded or artificial reefs. Large-scale studies face power supply challenges and require less intensive in-person surveys of recruited larvae (≤500 μm) and fish. Here, we present a preliminary assessment of artificial structure deployments with AE, conducted between July and September 2023 in Kane’ohe Bay (Oahu, Hawai’i). The artificial structures were designed to attract herbivorous juvenile reef fish and subsequently suppress algal growth. The work is part of a future artificial reef construction project in Hawai’i where in-person surveys and frequent battery replacements are logistically challenging. The deployments consisted of one control and one treatment site 65 m apart, in 5 m water depth and 10 m from the natural reef. To document ecosystem responses, both sites use open-source burst-mode autonomous cameras, a directional vector sensor seafloor acoustic recorder, and hydrophones. A 3.8 kW-h NiMh battery supply powers sound output for three weeks during evening hours. We discuss preliminary evaluations of AE and the validity of using autonomous cameras in evaluating performance in terms of fish recruitment and algal growth. [Work sponsored by DARPA.]