Environmental variables and bottom trawling effort affect the complexity and distribution of soft-bottom octocorals and burrowing megafauna communities in the Gulf of Cádiz

Bottom trawling significantly impacts benthic communities, reducing habitat complexity and biodiversity. The distribution and abundance of key species in the northeastern Gulf of Cádiz, Spanish waters of Atlantic Ocean, such as soft-bottom octocorals and burrowing megafauna, were examined using video observations and Spatial Distribution Models developed with Random Forest. The study was conducted in the Site of Community Importance “Volcanes de fango del golfo de Cádiz" focusing on depths between 300 and 950 metres depth. The effects of environmental variables and bottom trawling on octocoral distribution and abundance were assessed, and management strategies for habitat protection were proposed. Bottom trawling was found to decrease habitat suitability for large octocoral species while the abundance of Norway lobster was positively correlated with certain values of bottom trawling effort. The study suggests that bottom trawling causes significant reduction in octocoral distributions, substrate homogenization, and habitat differentiation. A 200 km area is recommended for a specific bottom trawling regulation to protect soft-bottom octocorals and support the recovery of commercial burrowing megafauna.

This work is supported by INDEMARES/CHICA (LIFE 07/NAT/E/000732), ISUNEPCA (FB FEP/AC1 20123118_2014; IEO/2015–2017), INPULSE and actions A.21 and A.4 of the LIFE IP INTEMARES (LIFE15/IPE/ES/000012) projects. Modelling was conducted in the Institute of Marine Research (Bergen, Norway), under the framework of the MAREANO Group, and was made possible thanks to a research grant from Fundación CEIMAR. Thanks to the different reviewers who have evaluated previous versions of the manuscript, whose contributions have been truly valuable.