Shallow coral reef community mapping and update on its ecological units using aerial images at Isla Arena, Colombian Caribbean

ABSTRACT

Remote sensing by unmanned aerial vehicles (UAVs) provides for obtaining large amounts of high-resolution data without direct intervention, which can be managed with geographic information systems (GIS). This allow spatial analysis of a habitat based on georeferenced data which is important to understand the structure and ecological distribution that are fundamental to ecosystems. Isla Arena (10°44ʹ20” N, 75°21ʹ10” W) is an inshore small shoal with a well-developed coral reef formation, despite the sedimentary influence of the Magdalena River in the Colombian Caribbean. Twenty years ago, habitat mapping of ecological units (EUs) of the area was carried out as a baseline study. In this study, we applied an analysis of remotely sensed aerial images, coupled with traditional in situ data to evaluate two different objectives. The first objective was to report the current ecological units in the reef formation with their respective distribution using a high-resolution orthophotomosaic to make a supervised classification based on the spectral reflectance of pixels and a spatial analysis of the reef formation. We evaluated 12 substrate components, of which eight were identified at the species level; then, seven EUs were defined in a thematic map. The second objective was to evaluate variations in the structure of the sessile community with underwater video transects to compare with a baseline study. We found that the coral cover remained similar but that seagrasses and zoanthids decreased in abundance, and macroalgae and sponge abundances increased, which could indicate reef degradation. The implementation of remote sensing by UAVs at Isla Arena was successful and provides a high-resolution alternative for describing the attributes of a shallow reef system. The comparison with the baseline study of the island allowed us to estimate the changes in the community structure and to update its EUs.

Acknowledgements

This study was funded by COLCIENCIAS (111-771-451-011) and the University of Magdalena in relation to the project “Acropora: a key genus for conservation. Genetic diversity, connectivity, and ecological updating of Acropora populations in the Colombian Caribbean”. We are grateful for the group of Ecology and Diversity of Marine Algae and Coral Reefs of the University on Magdalena.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

This work was supported by the Departamento Administrativo de Ciencia, Tecnología e Innovación (COLCIENCIAS) [111-771-451-011].