• Brittle star, J. Finn
  • Tropical brittle star wrapped around a coral, J. Finn
  • Tiny brittle star, C. Harding

The deep sea is one of the least explored areas on our planet. So little is known about this region that scientists aren’t even sure how biodiversity works at depths up to 6,500 meters (21,000 feet) below the sea surface.

But a study, published this week in Nature, starts the process of understanding more about how species are distributed across these sunken ecosystems, focusing on brittle and basket stars— close relatives of starfish. In providing this new information, the authors hope to establish a baseline for conservation efforts across the sea floor, which faces increasing pressures from deep-sea fishing and mining.

Why choose the brittle and basket stars as a focus? They’re not only widespread and diverse (with almost 3,000 species), but like their starfish cousins, they’re also “a dominant component of the fauna of many deep sea habitats,” according to the new study. The team assembled data from over 1,600 expeditions to understand the patterns of star diversity from the shallows, into the slopes of the continental shelf, all the way down to the deepest depths.

The researchers were surprised to find biodiversity patterns differed the deeper they dove into the data. In waters from zero-to-2,000 meters, diversity peaks in the tropics, where waters are warmer. Below 2,000 meters (6,500 feet) diversity peaks at mid-to-high latitudes, “particularly across the boreal Atlantic Ocean, around Japan, New Zealand, western North and South America and western Africa,” the team reports. And instead of water temperature playing a role as it does for shallower-water species richness, the scientists discovered that deep sea diversity correlates with high levels of energy transfer, or productivity (which reflects food availability), in the deeper waters.

In addition, the team’s findings suggest that the deep sea diversity is maintained by migrating shallow water species. “These results have important implications for identifying potential protected areas on the high seas,” they write, in the hope that this connectivity and the need for higher productivity will help inform conservation efforts in the deeper depths of the oceans.

Want to see these ecosystems for yourself? NOAA is live streaming exploration of the Mariana Trench from the Okeanos Explorer. For more information, click here. Wired reports that you can examine deep sea vents using virtual reality (VR). And check out a great dive into deep coral reefs, an area also known as the Twilight Zone, here. Finally, the Academy’s exhibit on the Twilight Zone, opening next month, will feature some of the bizarre live animals from these deeper depths.

Images: J.Finn and C. Harding, Museum Victoria

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