Galderic Lastras, CRG Marine Geosciences, University of Barcelona, Spain
Enric Ballesteros, Blanes Centre for Advanced Studies, CSIC, Spain
Josep-Maria Gili, Institute of Marine Sciences, CSIC, Barcelona, Spain
Anna Sanchez-Vidal, CRG Marine Geosciences, University of Barcelona, Spain
David Amblas, Scott Polar Research Institute, University of Cambridge, UK
La Fonera canyon, northwestern Mediterranean: A threatened cold-water coral habitat
Submarine canyons are known to be one of the morphological features where cold-water coral (CWC) ecosystems develop in the Mediterranean Sea, as observed in Cap de Creus and Lacaze-Duthiers canyons. La Fonera canyon, in the Catalan margin, Northwestern Mediterranean Sea, also was a good candidate to host such communities. Its head incises 28 km into the Catalan continental shelf and is formed by a complex network of three main branches (Cap de Begur, Illa Negra and Sant Sebastià) and many minor branches and gullies, with a rough terrain, high slope gradients and rock outcrops suitable for coral growth. The tip of Illa Negra branch is located at 60 m water depth at a distance of barely 800 m from the coastline.
After being mapped in detail in 2007 using a multibeam echosounder, the canyon head was the target of a systematic ROV survey, using a Seaeye Lynx 1500, at different environments and depths ranging between 79 and 401 m. ROV images evidence the presence and the status of CWC species Madrepora oculata and Dendrophyllia cornigera, gorgonian red coral Corallium rubrum, as well as human impacts taking place in their habitats. Terrain classification techniques have been applied to high-resolution swath bathymetric data to obtain semi-automatic interpretative maps to identify the relationship between coral distribution patterns and canyon environments.
Large, healthy colonies of M. oculata occur on abrupt, protected, often overhanging, rocky sections of the canyon walls, especially in Illa Negra branch. D. cornigera is sparser and evenly distributed at depth, on relatively low sloping areas, in rocky but also partially sedimented areas. C. rubrum is most frequent between 100 and 160 m on highly sloping rocky areas. The probable extent of CWC habitats has been quantified by applying a maximum entropy model to predict habitat suitability: 0.36 km2 yield M. oculata occurrence probabilities over 70%.
All ROV transects document either the presence of litter on the seafloor or pervasive trawling marks, with nets and longlines entangled on coral colonies, coral rubble observed at the foot of impacted colonies and partial burial of some colonies that could be the result of the resuspension generated by bottom trawling on neighboring fishing grounds, which has been demonstrated to be responsible of daily increases in sediment fluxes within the canyon.
Theme 3: Biological patterns in submarine canyons: role of scale and heterogeneity
La Fonera canyon, cold-water corals, Lophelia, anthropogenic impact, Mediterranean