Do colonies of Lytocarpia myriophyllum, L. 1758 (Cnidaria, Hydrozoa) affect the biochemical composition and the meiofaunal diversity of surrounding sediments?

Lytocarpia myriophyllum, the biggest hydroid of the Mediterranean, lives at soft bottoms. It is severely threatened by bottom trawling activities. To assess its possible influence on trophodynamics and biodiver- sity of surrounding sediments, we compared the organic matter content and biochemical composition, and meiofaunal biodiversity in sediments below L. myriophyllum colonies and in surrounding bare sediments. Below L. myriophyllum sediments, the protein to carbohydrate ratio, the lipid contents and meiofaunal abundance showed values higher than in bare sediments, suggesting that L. myriophyllum may influ- ence the availability of resources for benthic consumers. The richness of meiofaunal taxa and nematode species generally decreased from below the colonies to bare sediments suggesting that the presence of L. myriophyllum colonies can have a certain influence also on benthic biodiversity. The possible influence of L. myriophyllum on trophodynamics and biodiversity of neighbouring soft bottoms claims for efforts to increase our knowledge about the trophodynamics of mesophotic coral forests and to develop adequate measures of conservation of these important and threatened habitats.