Soundscapes of the central Red Sea mesophotic reef zones

Abstract

Despite covering a large amount of seafloor & representing a significant percentage of coral reef ecosystem biomass, Mesophotic Coral Ecosystems (MCEs) globally have been largely understudied in comparison to their shallow counterparts. The Red Sea is a unique and biodiverse tropical ecosystem, where few mesophotic coral reefs have been studied. To define spatiotemporal activity of marine life and characterize the soundscapes of the MCE in the Central Red Sea, two locations were surveyed at 70–80 m, as well as at two adjacent shallow reef sites at ∼10 m depth, respectively, during the winter (Jan 2022) and summer (Jul–Aug 2022) seasons. The results of this study, the first of its kind in the Red Sea, show a clear shift in the soundscape between seasons, as well as between the shallow and mesophotic zones, driven mainly by a change in fish and invertebrate chorusing. During the study periods, temperature and oxygen levels in the mesophotic zone remained relatively stable, in comparison to the shallow reef zone which saw a steep temperature increase and large diel fluctuations in oxygen in the summer. Chronic exposure to shipping noise is evident across Red Sea MCE soundscapes and the resulting potential effects are discussed.