The work, carried out by ICMAN-CSIC researchers, demonstrates the usefulness of these tools in ongoing programmes for Japanese invasive algae.
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Researchers from the Institute of Marine Sciences of Andalusia (ICMAN), which belongs to the Spanish National Research Council (CSIC), have demonstrated the usefulness of drone and satellite images for monitoring the species Rugulopteryx Okamura, an invasive macroalga from the Japanese coast that has spread rapidly along the Andalusian coast in recent years. The study has been published in an article in the journal Frontiers, which highlights the importance of incorporating these tools in continuous monitoring programmes for the species.
The publication presents a pilot monitoring study of this macroalga in which multispectral sensor images from drones and satellites have been combined with radiometric information obtained in situ on the coast. Specifically, the methodology has been developed based on a drone flight carried out on 1 July 2021 on Bolonia beach (Tarifa, Cadiz) together with the algae samples collected and the hyperspectral data captured with the field radiometer on the same day. In addition, medium and high spatial resolution satellite images from both Landsat-8 and Sentinel-2, close to that date, have been used.
“Thanks to the radiometric data, we have managed to characterise the spectral signatures of the algae, from the dry beach upwelling to the subtidal at a depth of 5 metres, so that we can generate a synoptic tool for monitoring the species in the future without the need to go there in person,” explains Mar Roca, a researcher at ICMAN-CSIC and co-author of the study.
The results obtained, after processing the different multispectral images using machine learning techniques, make it possible to map the emerged and submerged vegetation cover of this macroalgae. The drone images, which have a high spatial resolution (8.3 cm/pixel), show greater precision in delimiting and quantifying the area occupied by the algae, while those from the Sentinel-2 and Landsat-8 satellites, with 10 and 30 m/pixel spatial resolution, are capable of detecting its presence and generating continuous remote alerts.
“The importance of this study lies in the radiometric characterisation of the algae and the evaluation of this methodology to remotely monitor its distribution. Obtaining the cartography of the seabed and detecting where it is found beyond a depth of 5 metres is still an open line of research, but being able to detect the floating algae before it forms an upwelling on the beach can be a powerful tool for its operational management,” says Roca.
The study, led by ICMAN-CSIC, also involves researchers from the University of Nantes and the Consiglio Nazionale delle Ricerche (CNR). It is developed within the framework of the Sat4Algae project, funded by the Junta de Andalucía, and is a pioneer in evaluating the capacity of remote sensors on board drones and satellites as tools for monitoring invasive Japanese kelp, opening up a new approach to optimise its research and, therefore, its management.
Control of the species
In the European Union alone, macroalgae make up 40% of the marine invasive species of particular concern. This brown alga, Rugulopteryx Okamura, was first detected in 2015 off the coast of the Strait of Gibraltar, and its high rate of expansion has allowed it to colonise a wide range of habitats from 0 to 50 metres deep.
According to previous research, this invasive species is causing significant ecological impacts on the Andalusian coast, such as the loss of biodiversity, the alteration of the marine habitat and the displacement of native species. The economic consequences for the fishing and tourism sectors in the area have also been demonstrated.
This study demonstrates that satellite and unmanned aerial vehicle (UAV) images are useful for monitoring this species and would be an added value to the continuous monitoring programmes that currently exist. It could also be a tool to support the adaptation of regional, national and European policies, including the EU Biodiversity Strategy 2030, as well as the EU Targets to restore marine ecosystems.