Coral Reef Mapping with Remote Sensing and Machine Learning: A Nurture and Nature Analysis in Marine Protected Areas

Camila Brasil Louro Da Silveira,Ana Lídia Bertoldi Gaspar,Beatrice Padovani Ferreira,Gil Marcelo Reuss Strenzel,Mauro Maida

doi:10.3390/rs13152907

Camila Brasil Louro Da Silveira, Ana Lídia Bertoldi Gaspar + Show 3 more

Open Access

https://doi.org/10.3390/rs13152907

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Abstract

Mapping habitats is essential to assist strategic decisions regarding the use and protection of coral reefs. Coupled with machine learning (ML) algorithms, remote sensing has allowed detailed mapping of reefs at meaningful scales. Here we integrated WorldView-3 and Landsat-8 imagery and ML techniques to produce a map of suitable habitats for the occurrence of a model species, the hydrocoral Millepora alcicornis, in coral reefs located inside marine protected areas in Northeast Brazil. Conservation and management efforts in the region were also analyzed, integrating human use layers to the ecological seascape. Three ML techniques were applied: two to derive base layers, namely geographically weighted regressions for bathymetry and support vector machine classifier (SVM) for habitat mapping, and one to build the species distribution model (MaxEnt) for Millepora alcicornis, a conspicuous and important reef-building species in the area. Additionally, human use was mapped based on the presence of tourists and fishers. SVM yielded 15 benthic classes (e.g., seagrass, sand, coral), with an overall accuracy of 79%. Bathymetry and its derivative layers depicted the topographical complexity of the area. The Millepora alcicornis distribution model identified distance from the shore and depth as topographical factors limiting the settling and growth of coral colonies. The most important variables were ecological, showing the importance of maintaining high biodiversity in the ecosystem. The comparison of the habitat suitability model with species absence and human use maps indicated the impact of direct human activities as potential inhibitors of coral development. Results reinforce the importance of the establishment of no-take zones and other protective measures for maintaining local biodiversity.

Highlights

Coral reefs are considered hotspots of marine biodiversity and complex ecosystems, both ecologically and geomorphologically [1,2]
Our results showed that this species can be considered the coral with the highest occupation on the reefs of the area, even though Millepora alcicornis was not the most frequently occurring coral in number of colonies
The occupancy becomes more explicit when we consider the average size of Millepora colonies in comparison with scleractinian corals such as Siderastrea sp. and the other millepore occurring in the area, Millepora braziliensis

Summary

Introduction

Coral reefs are considered hotspots of marine biodiversity and complex ecosystems, both ecologically and geomorphologically [1,2]. These environments support socioeconomic activities and can be essential for the livelihood of millions of people [3,4] For these reasons, they are usually considered as priority conservation areas [5,6], in an effort to ensure the maintenance of coral reefs’ ability to provide their usual goods and services. They are usually considered as priority conservation areas [5,6], in an effort to ensure the maintenance of coral reefs’ ability to provide their usual goods and services Despite their importance, reefs around the world are in serious decline and are faced with a wide range of impacts, varying from local (e.g., population growth, pollution, erosion, coastal sedimentation) [1,7,8] to global threats (e.g., climate change, overfishing) [9,10]. Considering the combination of local and global effects, coastal reefs are affected, as they are usually subjected to intense and direct human impacts related to activities occurring in the reef framework [2,13,14]

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