Benthic habitat
Rodolith beds
Rhodolith is a specific morphotype of hard coralligenous formation that resembles small, branching nodules or pebbles of red, purple or pink colour. Rhodoliths are biogenic aggregations of photosynthetic algae species; such are Lithothamnion corallioides and Phymatolithon calcareum. They form and grow in a layered fashion, as they assimilate calcium carbonate from the surrounding water and develop in sizes ranging from a few millimeters to some centimeters. This is typically a slow process, and their growth rate is very low (0.4 to 1 mm/y). A seafloor that is characterized by high abundance of rhodoliths is referred to as a rhodolith bed. Rhodoliths are mostly found in muddy and sandy seafloors and have been recorded in shallow environments worldwide, like the Gulf of Mexico, Brazil, the Mediterranean Sea, the Great Barrier Reef, Malaysia and the Galapagos. While rhodolith beds are found in very shallow areas in tropical waters, in the Mediterranean Sea they form in the mesophotic zone (between 30-100 m depth) because of the elevated percentage of irradiance (photosynthetically available radiation, PAR) reaching the seafloor.
An essential and unique habitat
Rhodolith beds capture carbon and support diverse marine life by providing vital breeding, feeding, and sheltering grounds
Seafloor habitat mapping has become increasingly important to understand marine ecosystems and evaluate vulnerable habitats in a sufficient way. Hydroacoustics/echosounding methods constitute the most widely reliable tool for investigation and monitoring of seafloor characteristics (texture) and consequently the habitats extent in a high spatial resolution. Rhodoliths and rhodolith beds offer important ecological services since serve as blue carbon by sequestering atmospheric CO2 and storing it. They are also a vital part of the marine ecosystem as they act as breeding and feeding ground and provide shelter for a great number of marine species of fishes, invertebrates, crustaceans and mollusks.
Rhodoliths and coralligenous formations have low resilience and, consequently, they are very susceptible to anthropogenic activities such as dredging/fishing, anchoring, environmental pollution and the indirect effects of invasive species. In the Aegean Sea, the existing information suggests that these ecosystems are mainly found in waters deeper than 40 m, in the Cyclades plateau. A systematic marine remote sensing survey accompanied with ground truthing using side scan sonar, multibeam and R.O.V showed rhodoliths bed at the southwestern part of Preveza Gulf. The field consists of big-sized (20-30cm) rhodoliths of high spatial density and has been developed in soft seabed consisting of sandy mud. The bed was found in depths between 10 and 25 m covering an area more than 3.5 km2.
The spatial distribution of the beds strongly suggest that their presence is expected to be more extensive in the western Amvrakikos Gulf The knowledge of species compositions, dominant morphologies, proportion of living thalli and natural and anthropogenic pressures is essential for the protection and management of this very important ecosystem found in the entrance of a ecologically sensitive Gulf like that of Amvrakikos
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