20 Delightfully Strange New Deep Reef Species Discovered In “Underwater Hotels”

A treasure trove of deep reef dwellers has been discovered in coral reefs off the coast of Guam, including 20 that are new to science – and there could be more yet to come.

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Deep coral reefs like those in Guam exist at depths greater than 100 meters (330 feet) – which lies within the twilight zone – below the surface, which presents something of a problem to researchers trying to study the region.

“As deep-reef scientists, our biggest limitation in studying the mesophotic zone is time, due to the long decompression needed to ascend,” said Luiz Rocha, PhD, Curator of Ichthyology at the California Academy of Sciences, in a statement. “[W]e humans can only spend 15-25 minutes surveying at these depths.”

Then came a solution: autonomous reef monitoring structures, or ARMS. These devices act like artificial reefs, containing stacks of PVC plates with nooks and crannies that encourage sea creatures to make their home there.

“The autonomous reef monitoring structures, or ARMS […] are essentially small underwater hotels that coral reef organisms colonize over time,” explained Rocha. After a certain amount of time has passed, the plates are collected and scientists examine what’s within.

A series of ARMS were placed in deep coral reefs in Guam back in 2018. Finally, in November 2025, it was time to collect 13 of them.

It’s safe to say it was well worth the nearly decade-long wait.

“Two weeks of processing the ARMS plates yielded more data and species records than we’ve ever seen before in Guam at these depths, including cryptic invertebrates and previously undocumented communities,” said Robert Lasley Jr., PhD, Curator of Crustacea at the University of Guam.

Within the 2,000 specimens collected by the ARMS plates, there were 100 species that had never been recorded before in the region and 20 entirely new species. The specimens include a pink and yellow fish that reminds us of a gummy candy, a crab that we think might have got mixed up with a bowl of spaghetti, and, of course, what would any set of deep-sea species be without some weird and wonderful nudibranchs?

The final DNA analysis of the plates is yet to come, so it’s possible that researchers might find even more new species within them too.

But novel sea critters aren’t the only thing that the reef monitoring devices managed to capture. They also contained three years of temperature data from the upper twilight zone, which Rocha said provides “evidence of a clear and steady warming trend at depth.”

It’s hoped that both the biodiversity and temperature data will help to encourage and inform deep reef conservation efforts.

“Understanding twilight zone ecology, connectivity, and vulnerability is essential for effective conservation planning in a rapidly changing ocean,” said Rocha. “More than half of the species that live in deep reefs are unknown, yet these reefs are already being affected by fishing, pollution, and climate change.”

“Most marine protected areas only cover shallow reefs, pushing human-driven pressures towards deeper waters,” Rocha continued. “Our goal is to show just how beautiful, unique, and valuable these ecosystems are so we can safeguard them before it’s too late."