Mapping South Africa’s canopy forming kelp forests using low-cost, high-resolution Sentinel-2 imagery

• Published in: Estuarine, coastal and shelf science p. 108989
• Main Authors: Dunga, Loyiso, Lück-Vogel, Melanie, Blamey, Laura K., Bolton, John, Rothman, Mark, Desmet, Phil, Sink, Kerry
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.10.2024
• Subjects: coastal ecosystems; Kelp forests; Laminariales; marine mapping; remote sensing; rocky reef; Sentinel-2; rocky reef; Laminariales; Kelp forests; Sentinel-2; remote sensing; coastal ecosystems; marine mapping
• ISSN: 0272-7714
• DOI: 10.1016/j.ecss.2024.108989

Globally, kelp forests play a vital role in providing ecological, social and economic services. They contribute to the livelihoods and resilience of many coastal communities. To date, a gap exists in contemporary, comprehensive and consistent maps of South African kelp forests, since they were last mapped partially in 2006 by covering 900 km of South Africa’s coastline. This study addresses this gap by producing a comprehensive remotely sensed high-resolution 2016 map of canopy forming coastal kelp forests. Using the 10m resolution Sentinel-2 A and B spectral bands 4 (RED) and 8 (NIR), an expert derived Normalized Difference Vegetation Index (NDVI) threshold was used to detect surface protruding kelp forests along 1300 km coastline. The results were validated with expert verification and using Google Earth, data from historic maps, remote sensing and biomass estimation of South African kelp resources. Our study demonstrates the aptitude of Sentinel-2 for detecting canopy-forming kelps at low cost along South Africa’s west and south coast.. We report the encountered drawbacks in mapping an expansive coastline with varied sea conditions including wave activity, tides and turbidity. Comprehensive ground validation, long-term monitoring sites and the use of time series datasets remain a gap towards improving the calibration of remote sensing methods and long-term monitoring of South African kelp forests. Our results provide a foundation for continuous monitoring of South African kelp forests as well as exploring other unmapped kelp/similar habitats to inform research and environmental management. •An experimental, low-cost kelp mapping technique to advance high-resolution mapping of South African kelp forests•By applying NDVI thresholds, we mapped both surface-protruding and submerged kelp forests.•The results provide a consistent and comprehensive map of South African Kelp Forest ecosystems along a long and heterogeneous coastline.•Our study demonstrated the aptitude of Sentinel-2A and B coupled with expert knowledge for coastal ecosystem mapping.