Cyanobacterial Blooms affecting Circalittoral Vulnerable Benthic Communities in the Canary Islands

English. The present study was funded by the project ESMARES2 from the IEO-CSIC, under the framework of the application of the Marine Strategy Framework Directive (MSFD), ordered by the Ministerio de Transición Ecológica y Reto Demográfico (MITERD) of Spain.

English. Algae blooms are becoming more frequent throughout the world, causing significant impacts on the environment and even on human health. Benthic cyanobacteria, such as the species of the genus Lyngbya C.Agardh ex Gomont, are one more component of the communities of intertidal and subtidal habitats of all the oceans. Nevertheless, these species present the ability to grow rapidly under certain conditions, even forming blooms that dominate the habitat, and eventually, may affect the rest of the species in the community harmfully. In this study, we present the results of an oceanographic survey carried out on the southern coasts of Fuerteventura and Lanzarote in November 2021, where the massive presence of Lyngbya sp. (species yet to be confirmed genetically) was detected on circalittoral bottoms and at depths greater than 100 m. Dense populations of this species were recognized visually, sampling with ROV-T Tasife, and were also identified by live samples collected with the Liropus ROV. Lyngbya populations presented different colors, mainly depending on the depth, being dark red in the shallowest waters at 80 m and whitish at around 150 m. The accumulations of filaments of this alga overgrown the bed and all the benthic species found there, especially some vulnerable habitat-forming species: cnidarian species such as the black corals Antipathes furcata, Antipathella wollastoni or Stichopathes gracilis, or sponges such as different species of the Axinellidae family. This is the first study assessing the impact of the algae bloom on the circalittoral benthic environment of The Canary Islands.