JANUSSEN, Dorte; Forschungsinstitut und Naturmuseum Senckenberg: Sponges in deep water: A key to success

Deep-sea research utilizing hyperbenthic sampling devices has revealed unexpected high densities and diversity of sponges, and many of the recently collected deep-sea sponges are new species. Selected case studies in the Antarctic, North Atlantic and Mediterranean Sea show that this is true not only in hydrothermal environments but is a general feature of bathyal and abyssal areas in our oceans. Some groups of siliceous sponges are known to be a significant part of benthic life in the deep-sea, but the large populations of extremely small sponges and especially the documentation of rich associations of calcareans are new to science. So far, only five species of calcareous sponges have been described from depths below 2000 m, and the Calcarea were considered as a group of primarily shallow water animals. Organic sheats that cover the spicules of calcarean sponges, probably offers some protection and enables them to mineralize in spite of the high CO2 pressure.Special adaptations to soft bottom environments and alternative feeding strategies allow the sponges to thrive in deep-sea environments. The fossil resord of sponges goes back to the Late Proterozoic and also molecular data confirm that the Porifera are the oldest known metazoans. Palaeontological investigations have shown that sponges have been living in deep water at least since the Early Cambrian. The radiative success of sponges, particularly after extinction events in Earth`s history, may be linked with their ability to survive in the deep-sea.