Testing Side-Scan Sonar and Multibeam Echosounder to Study Black Coral Gardens: A Case Study from Macaronesia

Fernando Espino,Marcial Cosme de Esteban,Fernando Tuya,Francisco Otero-Ferrer,Mischa Schönke,Karolina Czechowska,Ricardo Haroun,Peter Feldens

doi:10.3390/rs12193244

Fernando Espino, Marcial Cosme de Esteban + Show 6 more

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https://doi.org/10.3390/rs12193244

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Abstract

Black corals (order Antipatharia) are important components of mesophotic and deep-water marine communities, but due to their inaccessibility, there is limited knowledge about the basic aspects of their distribution and ecology. The aim of this study was to test methodologies to map and study colonies of a branched antipatharian species, Antipathella wollastoni, in the Canary Islands (Spain). Acoustic tools, side-scan sonar (SSS), and a multibeam echosounder (MBES), coupled with ground-truthing video surveys, were used to determine the habitat characteristics of Antipathella wollastoni. Below 40 m depth, colonies of increasing height (up to 1.3 m) and abundance (up to 10 colonies/m2) were observed, particularly on steep and current-facing slopes on rocky substrates. However, coral presence was not directly imaged on backscatter mosaics and bathymetric data. To improve this situation, promising initial attempts of detecting Antipathella wollastoni by utilizing the MBES water column scatter in an interval for 0.75 m to 1 m above the seafloor are reported.

Highlights

In the current Anthropocene era, human activities have put the natural world under unprecedented danger
This study aims to increase the limited knowledge about the biological features of black coral gardens (A. wollastoni) off the Canary Islands, promoting much desired scientific research of these keystone mesophotic antipatharians occurring at depths of 25–100 m in other subtropical eastern Atlantic archipelagos (e.g., Cape Verde, Madeira, and the Azores)
Black corals gardens were not directly mapped in backscatter mosaics and bathymetric maps recorded by the multibeam echo sounder or side-scan sonar

Summary

Introduction

In the current Anthropocene era, human activities have put the natural world under unprecedented danger. Side-scan sonar (SSS) and the multibeam echosounder (MBES), have already been deployed to detect and study shallow-water marine habitats, such as coral reefs [12], seagrass meadows [13], and rhodolith beds [14], and deeper habitats, such as deep-water coral mounds [15,16,17]. Both tools emit sound beams narrow in the along-track direction that cover wide swathes of the seafloor perpendicular to the survey line and record the sound scattered back [18]. Both tools may be suited to detecting different seabed objects or may be complementary in their detection [22,23]

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