The false black coral Gerardia savaglia (Cnidaria, Zoanthidea) is a colonial hexacoral unable of creating branch-like colonies on its own. It invades gorgonian colonies and, partly or entirely, covers them over. This species is an important component of the twilight zone, usually presents at depth below 60 m. G. savaglia is considered a rare species and it is inserted in the Annex II ASPIM (Convention of Barcelona) and in the Appendix II of the Convention of Bern. During a research campaign held by ICRAM in the South Tyrrhenian Sea, a population of this species was discovered. The specimens were filmed and photographed by means of a Remotely Operated Vehicle (ROV), equipped with an underwater acoustic tracking position system, a digital camera (Nikon D80, 10 megapixel) with an underwater strobe (Nikon SB 400) and with two laser pointers 10 cm apart. High resolution multibeam data of the area were collected in order to create three-dimensional georeferenced distribution maps of G. savaglia in relation to depth, orientation and slope of the substrata. An area of 0.12 Km2 was covered and 3 ROV transects were executed between 20 and 90 m depth. G. savaglia was found only at depth range between 26 and 42 m. The population is composed by 28 colonies, subdivided in two different groups at a distance of 120 m. Colonies are mixed with a population of Paramuricea clavata. Calibrated distance between the two laser pointers was used to measure the colonies. Sizes of the measured specimens are between 22 and 87 cm in height, with a maximal base diameter of 8 cm. They were found on substrata with a North-East or North-West orientation that had slopes between 20°and 60° degrees. Few ecological studies on G. savaglia have been conducted until now, particularly due to the difficulty of working at the depth where it usually lives. Our results throw light upon the ecology of this species, pointing out the need for further studies.
Three- dimensional distribution of Gerardia savaglia in relation to depth, orientation and slope of the substrata in the South Tyrrhenian Sea
BO, MARZIA;
2009-01-01
Abstract
The false black coral Gerardia savaglia (Cnidaria, Zoanthidea) is a colonial hexacoral unable of creating branch-like colonies on its own. It invades gorgonian colonies and, partly or entirely, covers them over. This species is an important component of the twilight zone, usually presents at depth below 60 m. G. savaglia is considered a rare species and it is inserted in the Annex II ASPIM (Convention of Barcelona) and in the Appendix II of the Convention of Bern. During a research campaign held by ICRAM in the South Tyrrhenian Sea, a population of this species was discovered. The specimens were filmed and photographed by means of a Remotely Operated Vehicle (ROV), equipped with an underwater acoustic tracking position system, a digital camera (Nikon D80, 10 megapixel) with an underwater strobe (Nikon SB 400) and with two laser pointers 10 cm apart. High resolution multibeam data of the area were collected in order to create three-dimensional georeferenced distribution maps of G. savaglia in relation to depth, orientation and slope of the substrata. An area of 0.12 Km2 was covered and 3 ROV transects were executed between 20 and 90 m depth. G. savaglia was found only at depth range between 26 and 42 m. The population is composed by 28 colonies, subdivided in two different groups at a distance of 120 m. Colonies are mixed with a population of Paramuricea clavata. Calibrated distance between the two laser pointers was used to measure the colonies. Sizes of the measured specimens are between 22 and 87 cm in height, with a maximal base diameter of 8 cm. They were found on substrata with a North-East or North-West orientation that had slopes between 20°and 60° degrees. Few ecological studies on G. savaglia have been conducted until now, particularly due to the difficulty of working at the depth where it usually lives. Our results throw light upon the ecology of this species, pointing out the need for further studies.
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