Subsea Mountains in the South Atlantic-Brazilian Expedition uncovers striking biodiversity at the Rio Grande rise

The Rio Grande rise is located around 1,000 km from the Brazilian coast off the southern state of Rio Grande. This submerged mountain chain has its highest point located 580 meters below the surface of the ocean in a region where the mean depth is around 4,000 meters. The Rio Grande rise is the size of the Brazilian state of Bahia and is packed with a wide variety of marine life, many of which are unknown to scientists.

During the expedition researchers noticed that there was a greater number of whales and seabirds close to the rise than in other offshore areas. The project´s official name is Mar-eco Atlântico Sul, and can be considered as a sea life census. The last expedition was undertaken between November 7th and 15th of 2011, launching from the port of Itajai in the state of Santa Catarina and returning to Rio de Janeiro. Its main goal was to study the biodiversity in deep waters, looking at potential gain in biotechnology and a deeper understanding of climatic processes related to global warming, such as CO² absorption.

The project is led by the Itajai Valley University (Univali) in a partnership with the Ministry of Science, Technology and Innovation and with the Brazilian Navy, which pitched in by allowing the use of their oceanographic ship Antares. Another expedition is slated to take place sometime in 2012. The researchers believe that the rise exerts a wide influence in the whole water column from 4,000 meters to the surface. Many new forms of life such as deep water fish and invertebrates were found in different depth levels.

The Rio Grande rise in the west and the Walvis rise in the east are both perpendicular South Atlantic mountain chains which link the Atlantic ridge to the margins of South America and Africa. Researchers believe that both mountain chains influence the deep ocean water circulation in the South Atlantic, possibly influencing the dispersion of sea life in the deep ocean. Although these are generally areas with little amounts of nutrients, it is believed that the presence of the mountains actually help to increase the availability of nutrients, which may help sustain food chains in the region.

The expeditions have been ongoing since 2006 and up to now have already uncovered a highly significant, 6,000 potentially new species in the water column. It is quite possible that future expeditions may come to use more modern equipment such as AUVs and ROVs to help examine and search the deep ocean mountains, but up to know the expedition has been using more traditional research equipment such as deep water nets and dredges in order to collect specimens. 

Claudio Paschoa

Special thanks to Univali and Claudio Motta from O Globo