Invertebrate diversity associated with a shallow rhodolith bed in the Mediterranean Sea (Mar Piccolo of Taranto, south-east Italy)

Rhodoliths, formed by free-living coralline algae, are distributed worldwide, and the rhodolith beds (RBs) that they form are recognized as structurally complex habitats. In the Mediterranean, they are generally distributed in the mesophotic zone, at depths of 30–100 m; so far, only a few shallow RBs (<2 m) have been reported (e.g. Îles Kuriat, Tunisia, and Stagnone Marsala, Italy). Here a shallow-water RB located in the Mar Piccolo of Taranto (south-eastern Italy, Mediterranean Sea) is described. The diversity of associated invertebrates, the rhodolith-forming algal species, the type of sediments, and the bed extent are characterized. The RB investigated extends over 5 ha at depths of 0.5–1.5 m. The rhodoliths vary in shape and size, from pralines to large spherical structures, and are formed by a single species, Neogoniolithon brassica-florida, growing around nuclei of both natural and anthropogenic origin. The associated fauna consisted of 158 taxa, 79 (50%) of which were new basin records. The associated diversity was approximately twice that of the underlying and nearby sediments. The structural complexity of the RBs promotes biodiversity and provides shelter, food, and a breeding ground for numerous species, including seahorses, which are a conservation priority in this basin.