Understanding deep-sea diversity

Brittle stars shine a light on patterns in the deep

A tropical brittle star (image by Julian Finn).

A tropical brittle star (image by Julian Finn).

A team of scientists, including CEED researchers, have created the first map of seafloor diversity across the world’s oceans. The map reveals how patterns of biodiversity in the deep oceans fundamentally differ from those in shallow waters or on land.

Focusing on brittle and basket stars (related to starfish), the ground-breaking results were published in Nature.

“The deep seafloor remains the least explored ecosystem on Earth,” says Skipton Woolley, lead author on the study, from the University of Melbourne and Museum Victoria (and who is currently completing his PhD with CEED). “It is immense, remote and expensive to survey – so gaining accurate knowledge about the variety of life in the deep sea is difficult.”

To create the map, the team combined collection databases from museums around the world, then added information from scientific literature to create one ‘mega database’ which charts where marine invertebrate species have been found.

“We lack information about where seafloor animals are distributed and why some areas support more species than others,” said co-author Tim O’Hara, Senior Curator of Marine Invertebrates at Museum Victoria. “This is a problem for deep-sea conservation. It is very difficult to protect deep-sea animals and sustainably manage human activities such as deep-sea fishing and mining if we don’t know where animals live.”

New technology is making activities such as deep-sea mining for minerals including gold and cobalt increasingly viable.

Using sophisticated computer software, the team analysed the global distribution of thousands of species of brittle and basket stars to predict and measure patterns of where species occur across the seafloor. They were then able to use this data to compare biodiversity patterns across three different ocean depths: the continental shelf (20-200m), upper continental slope (200-2,000m) and deep-sea (2,000-6,500m).

“Our major finding is that patterns of biodiversity in the deep-sea differ from those on land or shallow water,” says Skipton. “The number of species peaks in tropical regions on land and in the sea down to 2000 metres. There are more species per square kilometre near the equator than there are in polar regions. In the deep-sea however, the number of species peaks at temperate latitudes, (between 30 and 50 degrees south and north). And deep waters off southern Australia, New Zealand and the North Atlantic are diversity hotspots.”

Brittle stars are helping researchers understand patterns of diversity at sea. Pictured above is the tiny brittle star (left, image by Caroline Harding)

Brittle stars are helping researchers understand patterns of diversity at sea. Pictured above is the tiny brittle star (left, image by Caroline Harding)

This surprising difference in diversity patterns can be explained by the amount of energy available to support life.

“Ecosystems on land and in shallow water receive energy from the sun – this energy is highest in tropical areas, which therefore support a higher number of species,” said Skipton.

“In the deep sea however, very little light or heat from the sun penetrates. Energy comes instead from microscopic animals and plants (plankton) that grow in the warm surface waters and ultimately sink to the seafloor to be consumed by hungry creatures living in the dark. There are more plankton in the southern and northern oceans than near the equator.”

The team hopes that as data from around the world is collected, global maps of seafloor diversity will continue to become more detailed, increasing our knowledge about the distribution of marine biodiversity. Such maps are crucial for managing the conservation and sustainable use of the deep oceans. The United Nations is currently negotiating a new international agreement for the management of the high seas through the UN Convention on the Law of the Sea. This research will help inform this process by identifying marine biodiversity in areas beyond national jurisdiction.

CEED researchers Brendan Wintle, Gurutzeta Guillera-Arroita and José Lahoz-Monfort from the University of Melbourne played an important role in building the statistical methods used as part of the study.


More info: Skipton Woolley swoolley@museum.vic.gov.au

Reference

Woolley SNC, DP Tittensor, PK Dunstan, G Guillera-Arroita, JJ Lahoz- Monfort, BA Wintle, B Worm & TD O’Hara (2016). Deep-sea diversity patterns are shaped by energy availability. Nature. doi:10.1038/nature17937. http://www.nature.com/nature/journal/vaop/ncurrent/full/nature17937.html

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