Monday, May 13, 2013

Ocean ridges not home to ‘more’ marine life

Undersea mountain ranges have long been thought to contain more marine life than flatter parts of the deep ocean, but now an international team of scientists has evidence that this is not the case. The findings have implications for how these areas should be managed and fished.

The scientists, from the University of Aberdeen and the Institute of Marine Research in Norway, say marine life gets sparser the deeper and further one gets from land, but that sea mounts and ridges have been considered to be areas of the mid-ocean where marine life is plentiful.

As such, they are attractive to high seas commercial fisheries, which operate in international waters beyond national jurisdiction.

The researchers have spent eight years investigating the Mid-Atlantic Ridge, the world’s longest mountain range, which rises to around 3,500 metres from the floor of the Atlantic Ocean, stretches from the Arctic to the Southern Ocean, and divides the ocean into eastern and western deep basins.

Using a range of sampling techniques and satellite imagery to study marine life, the team concentrated on the Charlie-Gibbs Fracture Zone, where two vast canyons cut across the Northern Mid-Atlantic Ridge, a marine protected area.

Professor Monty Priede, director of Aberdeen’s Oceanlab, said mid-ocean ridge areas such as the Charlie-Gibbs Fracture Zone were rich feeding grounds. Many animals such as birds, dolphins and whales feed there, and the areas are also used by deepwater fisheries. “However our studies, which analysed food production and availability, showed that the volume of life mid-ocean would be the same if there was no ocean ridge, although the type of animals that would live there would be completely different,” Priede said.

“The ridge has the effect of compressing all marine life together into a thin layer, so you have the attaching animals such as corals, sponges and sea lilies, the burrowing and crawling animals such as worms, sea cucumbers, brittle stars, star fish, crabs and sea spiders, as well as the swimming animals such as fish – all crowded over the summits, slope and terraces that make up the ridge.

“If there was no ridge there would be different animals, such as free-floating and swimming creatures, including deep sea luminescent fish, jellies, krill and squid, which would be distributed throughout 3.5 kilometres depth of water. “There is no doubt that the presence of the Mid-Atlantic Ridge greatly alters the water circulation and biology of the Atlantic Ocean, providing habitat for deep sea animals that would otherwise not survive in mid ocean, including commercial fish species attracted to the summits.”

But Priede said the ridge did not increase biological productivity of the mid-ocean and this needed to be taken into account when considering fishing in these areas. Fortunately, the Charlie-Gibbs marine protected areas were a remarkable example of international cooperation to conserve offshore resources.

Although the scientists discovered new species during their trips, they also established that most of the animals on the Mid-Atlantic Ridge also live at the same depths on the continental slopes around the edges of the oceans. Marine geneticists also found that fish on the ridge and the edges of oceans are closely related, suggesting that they move freely across the Atlantic Ocean.

While the ridge does harbour some species not found elsewhere, its main importance seems to be as a stepping stone for species to spread across the ocean.

Read the original article here.

Source: University World News
Image courtesy of milan.boers via Flickr (CC BY 2.0)