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Remote Sens. 2017, 9(7), 705; doi:10.3390/rs9070705

High Resolution Orthomosaics of African Coral Reefs: A Tool for Wide-Scale Benthic Monitoring

1
Dipartimento di Scienze della Vita e dell’Ambiente (DISVA), Via Brecce Bianche, Monte Dago, 60130 Ancona, Italy
2
Cranfield Institute for Resilient Futures, School of Water, Energy and Environment, Cranfield University, Cranfield MK430AL, UK
3
UBICA srl (Underwater BIo-CArtography), Via San Siro 6/1, 16124 Genova, Italy
Cranfield Institute for Resilient Futures, School of Water, Energy and Environment, Cranfield University, Cranfield MK430AL, UK
*
Author to whom correspondence should be addressed.
Academic Editors: Stuart Phinn and Xiaofeng Li
Received: 27 March 2017 / Revised: 23 June 2017 / Accepted: 4 July 2017 / Published: 8 July 2017
(This article belongs to the Section Ocean Remote Sensing)
View Full-Text   |   Download PDF [10846 KB, uploaded 8 July 2017]   |  

Abstract

Coral reefs play a key role in coastal protection and habitat provision. They are also well known for their recreational value. Attempts to protect these ecosystems have not successfully stopped large-scale degradation. Significant efforts have been made by government and research organizations to ensure that coral reefs are monitored systematically to gain a deeper understanding of the causes, the effects and the extent of threats affecting coral reefs. However, further research is needed to fully understand the importance that sampling design has on coral reef characterization and assessment. This study examines the effect that sampling design has on the estimation of seascape metrics when coupling semi-autonomous underwater vehicles, structure-from-motion photogrammetry techniques and high resolution (0.4 cm) underwater imagery. For this purpose, we use FRAGSTATS v4 to estimate key seascape metrics that enable quantification of the area, density, edge, shape, contagion, interspersion and diversity of sessile organisms for a range of sampling scales (0.5 m × 0.5 m, 2 m × 2 m, 5 m × 5 m, 7 m × 7 m), quadrat densities (from 1–100 quadrats) and sampling strategies (nested vs. random) within a 1655 m2 case study area in Ponta do Ouro Partial Marine Reserve (Mozambique). Results show that the benthic community is rather disaggregated within a rocky matrix; the embedded patches frequently have a small size and a regular shape; and the population is highly represented by soft corals. The genus Acropora is the more frequent and shows bigger colonies in the group of hard corals. Each of the seascape metrics has specific requirements of the sampling scale and quadrat density for robust estimation. Overall, the majority of the metrics were accurately identified by sampling scales equal to or coarser than 5 m × 5 m and quadrat densities equal to or larger than 30. The study indicates that special attention needs to be dedicated to the design of coral reef monitoring programmes, with decisions being based on the seascape metrics and statistics being determined. The results presented here are representative of the eastern South Africa coral reefs and are expected to be transferable to coral reefs with similar characteristics. The work presented here is limited to one study site and further research is required to confirm the findings. View Full-Text
Keywords: seascape metrics; structure-from-motion; FRAGSTATS; photogrammetry; sampling scale; quadrat density; sampling strategy; sampling framework seascape metrics; structure-from-motion; FRAGSTATS; photogrammetry; sampling scale; quadrat density; sampling strategy; sampling framework
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Palma, M.; Rivas Casado, M.; Pantaleo, U.; Cerrano, C. High Resolution Orthomosaics of African Coral Reefs: A Tool for Wide-Scale Benthic Monitoring. Remote Sens. 2017, 9, 705.

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