A quantitative comparison of towed-camera and diver-camera transects for monitoring coral reefs

• Published in: PeerJ (San Francisco, CA) Vol. 9; p. e11090
• Main Authors: Cresswell, Anna K, Ryan, Nicole M, Heyward, Andrew J, Smith, Adam N H, Colquhoun, Jamie, Case, Mark, Birt, Matthew J, Chinkin, Mark, Wyatt, Mathew, Radford, Ben, Costello, Paul, Gilmour, James P
• Format: Journal Article
• Language: English
• Published: United States PeerJ. Ltd 14-04-2021; PeerJ, Inc; PeerJ Inc
• Subjects: Benthic; Cameras; Conservation Biology; Coral reef monitoring; Coral reefs; Coral reefs and islands; Digital cameras; Ecology; Environmental monitoring; Mapping; Marine Biology; Marine environment; Methodology; Methods; Methods comparison; Polls & surveys; Surveys; Towed video; Vehicles, Remotely piloted; Benthic; Image analysis; Methodology; Technology; Towed video; Mapping; Coral reef monitoring; Methods comparison
• ISSN: 2167-8359; 2167-8359
• DOI: 10.7717/peerj.11090

Novel tools and methods for monitoring marine environments can improve efficiency but must not compromise long-term data records. Quantitative comparisons between new and existing methods are therefore required to assess their compatibility for monitoring. Monitoring of shallow water coral reefs is typically conducted using diver-based collection of benthic images along transects. Diverless systems for obtaining underwater images (e.g. towed-cameras, remotely operated vehicles, autonomous underwater vehicles) are increasingly used for mapping coral reefs. Of these imaging platforms, towed-cameras offer a practical, low cost and efficient method for surveys but their utility for repeated measures in monitoring studies has not been tested. We quantitatively compare a towed-camera approach to repeated surveys of shallow water coral reef benthic assemblages on fixed transects, relative to benchmark data from diver photo-transects. Differences in the percent cover detected by the two methods was partly explained by differences in the morphology of benthic groups. The reef habitat and physical descriptors of the site-slope, depth and structural complexity-also influenced the comparability of data, with differences between the tow-camera and the diver data increasing with structural complexity and slope. Differences between the methods decreased when a greater number of images were collected per tow-camera transect. We attribute lower image quality (variable perspective, exposure and focal distance) and lower spatial accuracy and precision of the towed-camera transects as the key reasons for differences in the data from the two methods and suggest changes to the sampling design to improve the application of tow-cameras to monitoring.