“Jurassic Park of sponges” discovered in the Mediterranean Sea
Press Release Date: May 28, 2015
Spanish researchers have published[i] in PLoS ONE the discovery of a ‘rock’ sponge reef unique in the world. The structure, of which its kind was thought to have been extinct millions of years ago, was discovered at a depth of 760 metres surrounding the top of a small seamount between Valencia and Ibiza where drilling for hydrocarbons has been planned. It was formed by the species Leiodermatium pfeifferae, a sponge that until now was only known in the Atlantic, from Macaronesia as far as the Caribbean, making it the first record of this species in the Mediterranean.
“The lithistid sponges are generally referred to as ‘rock’ sponges because they are hard and rigid like rocks due to a massive skeleton comprised of pieces of silica, a material identical to the glass in a window. The living tissue is minimally developed and is usually less than 5% of the total weight of the sponge,” explains Manuel Maldonado, a specialist in sponges at the Blanes Centre for Advanced Studies, Council for Scientific Research (CEAB-CSIC), which led the study in collaboration with researchers from the Spanish Institute of Oceanography (IEO) and from Oceana. “Understanding the conditions that enabled the development of this reef in this particular Mediterranean seamount will provide important clues to the understanding of how these unique Jurassic sponge reefs form and the reasons for their disappearance – a decline that occurred almost concurrently to that of the dinosaurs,” adds Dr. Maldonado.
Silica reefs, built by sponges and not corals, were common in the Jurassic and Cretaceous seas but thought to have been extinct. To general surprise, in 1987, a live silica reef was discovered at a depth of 200 m in the Canadian Pacific coast, formed by hexactinellid sponges (‘glass sponges’). The reef that has now been discovered featuring the ‘rock’ sponges is an even rarer type of reef, since the vast majority of the ‘rock’ sponges species became extinct after the Cretaceous period. The relatively few species surviving today are confined to tropical and temperate deep waters and were thought to have lost their ability to form reef-like aggregations.
“The rock sponge reef is an exceptional discovery. It is a unique formation on the planet that must urgently be protected because the place where it has been found is being subjected to various pressures, including plans for the exploration and exploitation of hydrocarbons,” says Ricardo Aguilar, Director of Research at Oceana and co-author of the study. “Although Spain has recently taken an important step towards increasing marine protected areas with the LIFE+ INDEMARES project, further efforts are needed to meet national, European and international conservation objectives. Such spectacular and unique places cannot be omitted from these plans.”
The sponge aggregations which reach almost a metre and a half in height were found using a submarine robot aboard the Oceana Ranger which enabled the filming and collection of information on species associated with this ecosystem, such as other sponges, corals, gorgonians, deep-sea crabs, conger eels, amogst others.
Most of the functional aspects of this unique habitat (food, reproduction, growth, longevity etc.) are still yet to be thoroughly investigated. Researchers fear that plans for the prospecting of hydrocarbons in the Balearic Sea may affect the unique reef discovered, which could be severely damaged before it can be properly studied.
According to the scientific article published in the journal PLOS ONE, the studies carried out in the area around the Balearic Islands have indicated this sponge can also be found on another important seamount, Emile Baudot. However, the sponges although plentiful in places at this other site have not managed to create the same ‘rock’ reef formation.
[i] Maldonado M, Aguilar R, Blanco J, García S, Serrano A, Punzón A (2015) Aggregated Clumps of Lithistid Sponges: A Singular, Reef-Like Bathyal Habitat with Relevant Paleontological Connections. PLoS ONE 10(5): e0125378. doi:10.1371/journal.pone.0125378