Deep-sea sponges in a Mediterranean cave

Submarine caves share several ecological features with deep-sea habitats and could be considered as a natural mesocosm of the bathyo-abyssal zone, despite differences in temperature. A unique Mediterranean cave which entraps a cold water mass, resulting in stable temperature conditions throughout the year, is a specially interesting 'bathyal island' in the littoral zone. It has been colonized by deep-sea invertebrates, whose likely source of propagules is a nearby canyon, 100 to 3000 m deep. The example of sponges shows that various general problems of deep-sea biology could be successfully addressed in the cave. A representative of tile deep-sea hexactinellid sponges reproduces here year round - enabling the first observations of larval behaviour and ultrastructure to be carried out on this phylogenetically important group of invertebrates, and opening the unknown field of larval ecology of deep-sea sponges. The presence of a species of the deepest known genus of sponges, Asbestopluma (at 8840 m depth in the Central Pacific), is a fascinating opportunity to investigate the biology of the strange deep-sea cladorhizid sponges, which can live in the most oligotrophic abyssal basins. A highly unexpected result is that cladorhizids are non-filter-feeding ''sponges'' with a carnivorous feeding habit.