Distribution patterns and demographic trends of demosponges at the Menorca Channel (Northwestern Mediterranean Sea)

Nowadays, there is still a huge lack of knowledge regarding the morphology and size structure of sponge populations and their possible ecological implications. This study assesses, by means of quantitative analyses of video transects and morphometric analyses on still photographs, the geographical, bathymetrical and size-structure distribution of the most relevant habitat-forming sponge species on the continental shelf and the upper slope of the Menorca Channel, an area soon to be declared a Marine Protected Area (MPA) as part of the Natura 2000 Network. Additionally, the influence of seafloor variables on the observed distribution patterns was evaluated. Highest sponge densities and abundances were concentrated in areas of high hydrodynamism, namely the rocky shoals offshore Cap Formentor and the Menorca Canyon's head. Most of the studied species were dominated by small to medium size classes, suggesting pulse recruitment events. A clear depth-zonation pattern has been observed, going from the inner continental shelf to the upper slope. At the same time, the continental shelf harbored the presence of diverse and contrasting growth morphologies, yet the biggest forms occurred at the shelf edge and the upper slope. This study highlights the presence of dense, well-preserved sponge populations in the Menorca Channel, and provides a baseline for their future monitoring once the MPA is declared, potentially serving as reference for other areas across the Atlanto-Mediterranean region.