“The deep seafloor remains the least explored ecosystem on Earth,” said lead author Skipton Woolley, from the School of BioSciences, University of Melbourne and Museum Victoria.

This area exists from 2k to as far as 6.5k deep, and covers 70% of the ocean’s seafloor.

“We have an innate understanding of the important regions of biodiversity on land, but are much less aware of what is going in the deep-sea,” says Mr Woolley.

“It is immense, remote and expensive to survey – so gaining accurate knowledge about the variety of life in the deep sea is difficult.”

Over the past two decades, the team has visited museums around the world and combined their collection databases with information from scientific literature to create one ‘mega database’, which charts where marine invertebrate species have been found.

There are over 2000 species of brittle and basket stars, and they are found in all oceans, from coastal areas, to polar regions.

Using sophisticated computer software, the team of researchers from Australia, Canada and the United Kingdom 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).

The ARC Centre of Excellence for Environmental Decisions (CEED) and BioSciences researchers Associate Professor Brendan Wintle, Dr Gurutzeta Guillera-Arroita, and Dr José Lahoz-Monfort have particular expertise in the statistical methods used in the study.

“Our major finding is that patterns of biodiversity in the deep-sea differ from those on land or shallow water,” says Mr Woolley, who is currently completing his PhD with CEED.

“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).

“Deep waters off southern Australia, New Zealand and the North Atlantic are diversity hotspots.

“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 Mr Woolley.

“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.