New data on the distribution of the ‘deep-sea’ sponges Asbestopluma hypogea and Oopsacas minuta in the Mediterranean Sea

Abstract

The sponges Oopsacas minuta (Hexactinellida) and Asbestopluma hypogea (Demospongiae, Cladorhizidae) belong to groups that are typical of deep water, but both species have already been recorded from the shallow water Trois Pepes cave at La Ciotat (Marseille area). We here report on subsequent findings of A. hypogea in two other littoral caves: one at Garmenjak Island in the Middle Adriatic (Croatia), the other at Jarre Island (Marseille, France). The maximum temperatures experienced in situ by these populations are significantly higher than those from the deep Mediterranean Sea, but they are also up to 6°C higher than those reported for the Trois Pepes cave population, up to 23.1 °C in July 2002 for Garmenjak population and 22.8 °C in August 2004 for Jarre population (exposures from a few hours to a few days). The average summer temperature inside both caves remains several degrees lower than the outside temperature at the same depth. Long time survival of A. hypogea populations at the relatively high summer/autumn temperatures in both Jarre cave (4 years monitoring) and Garmenjak cave (5 years monitoring) indicates that the species can successfully colonise such shallow habitats in spite of its presumed deep-water origin. We also report of additional cave records of O. minuta from the Middle Adriatic (Croatia): at Hvar Island in the marine part of the Živa Voda anchialine cave, and from the marine caves at Iski Mrtovnjak, Lastovo and Fraskeric Islands. The wide distribution of this species in the deep Mediterranean is substantiated by a record on Santa Lucia Bank north of Corsica (303 m) and photographs taken by the submersible Cyana in the Central Tyrrhenian Sea (2912 m, 2845 m) and the Ionian Sea (2447 m). Possible colonisation patterns of littoral caves by both sponges are discussed.