Presence of Corallium rubrum on coralligenous assemblages below 50 m along Calabrian coast (South Italy)

The presence of red coral, Corallium rubrum (Coralliidae, Gorgonacea) was reported during a monitoring study on biodiversity of hard bottom substrata along the coast of Calabria. A total of 52 transects at depths ranging between 50 and 200 m were surveyed by means of a Remotely Operated Vehicle (ROV). The ROV was equipped with a digital camera and with two laser pointers placed 10 cm apart and used as metric scale. We found colonies in 20% of the surveyed areas. Red coral is endemic to the Mediterranean Sea and it is one of the key engineering species of coralligenous assemblages. Due to its high commercial value it has been long overexploited and it is now a protected species. Although mixed-gas diving systems can extend the SCUBA range to slightly more than 100 m, there were very little quantitative information on populations deeper than 50 m. Quantitative data on the spatial distribution and population structure of the red coral along the southern Tyrrhenian and Ionian coasts of Calabria were collected. Colonies have been photographed and filmed. Presence, patch frequency, density, and parameters describing colony morphology were recorded. Red coral was observed between 70 and 130 meters depth. On rare occasions the presence of larger colonies (about 20 cm high) was recorded. More often we found smaller colonies (about 1 - 6 cm high), which showed only rudimentary branching patterns (primary and secondary branches). The presence of some dead colonies was also recorded. C. rubrum colonies were generally single or grouped in small patches of 3 – 4 specimens. Only in the southernmost area we found that this species was the dominant component of the coralligenous zone with a maximum density of ~ 90 colonies/m2.