Rhodolith/ Maerl Beds: A Global Perspective

Abstract

The available references to rhodolith beds have been analyzed for a total of 125 locations in the Mediterranean Sea, equally distributed in the eastern and western sub-basins. Mediterranean rhodolith beds occur from 9 to 150 m of water depth, with a mean depth of about 55 m in both sub-basins. Most rhodolith beds lay within the depth range 30–75 m, while those extending deeper than 75 m are about 18 % of the total, and those shallower than about 25 m are uncommon. The deepest and the largest Mediterranean rhodolith beds are both located in the Balearic Sea. Water motion from bottom currents, waves, and tides is needed to keep rhodoliths unburied, within mesotrophic to oligotrophic water conditions. Rhodolith beds are commonly small (<0.01 km2) and multispecific, showing growth-form mixing and a much higher coralline biodiversity than Atlantic beds. They are vulnerable to physical disturbance by fishing gears and smothering, and to water pollution by organic enrichment and sewage. The existing instruments of legal protection appear ill defined, since these are based on scientific literature mostly derived from northern Europe, where specific and different environmental settings, species composition, depth distribution, and anthropogenic pressures occur. The protection of a specific habitat type cannot be effectively gained without access to geospatial and compositional data and an increased research effort is needed to improve taxonomic inventories, habitat mapping, and monitoring activities on a basin scale.