Hydrothermal vents can be found on all oceans and often in volcanically active areas, as in the Azores, but only recently were they discovered. To humans, hydrothermal vents are rather hostile environments but to other organisms, hydrothermal vents are a paradise: the density of organisms around vents are 10 000 to 100 000 times higher than on the surrounding seafloor.
It was in 1977, when scientist were exploring the ocean ridge in the eastern Pacific and measuring the water temperatures along the Galapagos Rift, that they noticed that in some areas the temperatures jumped from almost freezing to over 400°C within a couple of meters. What they had discovered were hydrothermal vents; little cracks and fissures in the planet’s surface from which heated liquid escapes, similar to geysers and hot springs on land. Due to the high pressures in the deep ocean the water does not evaporate and can reach 450°C or more.
Bacteria can break down sulphur compounds from the vents, highly toxic to most organisms. These bacteria form the base for a food chain: they grow thick layers and attract small planktonic crustaceans (amphipods and copepods) that graze on the bacteria. The bacteria and small crustaceans sustain an entire food chain of snails, worms, shrimp, bivalves and crabs creating a whole ecosystem of predators and preys.
Hydrothermal vents bring heat and minerals from the inner of the earth to the surface and play an important role in the ocean’s chemistry; at the same time they create deposits of minerals on the ocean floor.
The protection of hydrothermal vents is key to preserve this unique habitat, its biodiversity and its geological importance. It is also a precautious measure for potential exploitation and deep-sea mining. In the offshore marine protected areas of the Azores, commercial and recreational fishing activities are allowed and regulated.
In the Azores archipelago three deep hydrothermal areas, as well as one shallow area with hydrothermal activity are under protection.
The deepest field, the Rainbow Hydrothermal Field, is located about 200 nautical miles southeast of Faial Island and lay at about 2300 meter depth.
This hydrothermal field is about 180 nautical miles southeast of Faial at a depth of 1700 meters and the largest known hydrothermal field in the archipelago. Its vents spread over 150 square kilometres and reach temperatures of over 330°C. Lucky Strike is characterized by “black smokers”: springs oversaturated with salts and metals giving them a black, smoke-like appearance. Shrimps and mussels dominate the Lucky Strike fauna.
The Menez Gwen field lies in a line with the Lucky strike field and the Rainbow field. It is a submarine volcano that rises 700 meters from the seafloor with a 17 kilometres diameter. The Menez Gwen Field lies at about 840 meter depth close to the top of the volcano on its southeast side. Similar to the Lucky Strike field, the Menez Gwen field is characterised by shrimp, mussel and crab species.
Dom João de Castro Bank
The fourth protected area with hydrothermal activity is the Dom João de Castro Bank, located between Terceira Island and São Miguel Island. The Volcano rises from 1000 meters of depth to 13 meters below the surface at its highest point. Inside the crater it slopes down to 50 meters of depth. Dom João de Castro Bank has the typical characteristics of a seamount, but combined with hydrothermal activity.
The areas last major volcanic eruption was recorded in 1720 and resulted in the formation of a small island, Ilha Nova (New Island), app. 1.5 kilometres in diameter and reaching 250 meters of altitude. By 1722 the newborn Ilha Nova had already disappeared below the surface. Due to limited documentation at the time, the existence of the island was disputed until 1941 when the former island was located and mapped.The area was then named after the Portuguese explorer of the 16th century – D. João de Castro.
Before being protected, the Dom João de Castro Bank was under great commercial fishing pressure that was affecting the entire ecosystem. Today the area has two levels of protection: the Marine Reserve (1) of D. João de Castro being more restrictive to human activities than the Managed Resource Area (2) of D. João de Castro.
The D. João de Castro Bank is one of the best accessible areas for divers to explore in a seismically active area. There are hydrothermal vents located at only 20 meter depth that can reach temperatures of up to 120° C. At different locations gases, mainly carbon dioxide, can be seen rising up to the surface. These geological features make the D. João de Castro Bank a very unique location, for recreational diving as well as for scientific studies.