New data on occurrence of thermophile Scleractinia (Cnidaria, Anthozoa) in the Phlaegrean Island (Ischia, Procida, Vivara, Gulf of Naples), with special attention to Astroides calycularis

Abstract

Biogeographia vol. XXV - 2004 (Printed December, 30 q' 2004) Marine Biogeography of the Mediterranean Sea: patterns and dynamics ofbiodiversity New data on occurrence of thermophile Scleractinia (Cnidaria, Anthozoa) in tl1e Phlaegrean Islands (lschia, Procida, Vivara, Gulf of Naples), with special attention to /lstroicles cal)/cu/arts MARCO DAPPIANO°*, MARIA CRISTINA GAMBI* ° [CR/LM, via dz’ Czzsrzlotti 300, Roma (Italy). Ttzborzztario di Ecologirz del Bent/705, Stzzzione Zoologiaz qA. Do/7m ”, Pzmtzz San Pietro —./380077 Isc/7221 (Nzzpoli, Italy) Key words: Scleractinia, Afiroitler a1/you/zzrir, distribution, marine cave, Tyrrhenian Sea. SUMMARY Ntw data on occurrence and distribution of some Scleractinia (Cnidaria, Arithozoa) with thermophile affinity were presented for the area comprising the Phlaegrean islands (lschia, Procida and Vivara, Gulf of Naples Tyrrhenian Sea). Data were obtained by means ofvisual census and photographic sampling in 21 sites located all around the islands on rocky cliffs, rocky banks and semi-obscure caves. Four species with thermophile affinity were recorded: Clzzdocorzz czzerpitarzz (Linneo, 1767), Mzzzlraa‘.tp/rzzmzsis (Heller, 1868), P/Jyllzmgzlz mom:/aezii (Lacaze—Duthiers, 1897), and Artroides mlym/izrir (Pallas, 1766). Both M. plmremir and P. mozrr/Jezii were first reported for the studied area after our study. The most widespread and frequent species was C raertaitara, occurring in almost all studied sites in photophilious biotopes within the first 15-20 m depth. M. 127/1zzremz': was particularly abundant in the “Grotta Grande” of the bank “Formiche of Vivara”, where it formed a large flzcie: on the cave ceiling. P. mam‘/Jezii was the most occasional specie occurring with few colonies in three sites between 25 and 40 m depth. For A. nzlycztlrzris a specific study on abundance pattern and population structure was performed in three stations (two inside of a semi—submersed, semi—obscure cave and one along the shadowed cliff off S. Angelo). A. czzlyrztldrzk showed very high densities in the zone 0-1 m depth, mainly consisting of young specimens (1—3 corallites). Density showed a dramatic decrease below 3 m depth in the two stations inside the cave, while in S. Angelo density started to decrease below 6-8 m depth. Inside of the cave, comparison with previous observations from an earlier ecological study performed in 1976, revealed that the species has strongly increased its abundance and coverage, extending its colonization to the entire perimeter of the cave, including a long and narrow siphon and a large inner chamber (from approx. 56 ml of bottom colonized in 1976 to approx. 418 m” in 2003). The high frequency, and extension of/1. m{yt‘zz/zzri: in the studied area can be favored by changes in the hydrographic conditions in the southern Tyrrhenian Sea and in the Gulf of Naples. In fact, an overall slight warming of the superficial waters has been recorded in some periods in the Gulf. Longer water mass summer stratification and increase of winter minimum were occasionally recorded. This inter—annual variability, with some years or longer periods of warming of the superficial waters, may be an important factor for the reproductive success of the species, which in these periods can favor more intensive offspring production and increase successful settlement of new recruits that may lead to the increased colonization observed. A. rzzlym/zzrir, especially in those areas such as the Gulf of Naples near to its northern distribution limit, should be therefore considered as a good “biological indicator” at short and rnedium—term scale, to reveal ongoing climatic changes.