In a Part of the Pacific That's Hard to Reach, New Discoveries

The twilight zone of the Pacific just got the teeniest bit less mysterious. Scientists from the California Academy of Sciences say they believe they've uncovered at least 20 previously unknown species living on deep coral reefs off Guam. They came to that conclusion after hauling up 13 monitoring devices that had been quietly gathering data since 2018. The autonomous reef monitoring structures, or ARMS, were placed as deep as 330 feet—an upper slice of the ocean's dim "twilight zone" where sunlight is scarce and pressure is high.

That area is "difficult, expensive and dangerous to reach," per CNN—doing so requires a submarine, remotely-operated vehicle, or advanced technical divers. "While we humans can only spend 15-25 minutes surveying at these depths, ARMS have been collecting data 24/7 for years," California Academy of Sciences ichthyology curator Luiz Rocha explains. And so in November, divers retrieved what Rocha likens to "small underwater hotels that coral reef organisms colonize over time." The layers of 1-foot-square PVC plates essentially create artificial reefs that animals make their home. The 13 devices the team collected yielded about 2,000 specimens, including 100 species never before recorded in the region.

Rocha tells NPR that the final tally of new species may even exceed the suspected 20, because every specimen is run through DNA sequencing to confirm whether it's truly new. That process sometimes reveals hidden diversity: organisms that look familiar but turn out to be genetically distinct. Early contenders for new-to-science status include crabs, sponges, sea squirts, and gorgonian corals. One find stood out even to seasoned deep-reef divers: a hermit crab that had ditched the usual snail shell for a clamshell home.

The Guam work is just the start. Rocha's team has launched a two-year effort to pull up 76 ARMS devices scattered across the Pacific, including off Palau and French Polynesia. As a press release explains, "The resulting data will not only build the world's most comprehensive baseline of upper twilight zone biodiversity, but also provide critical insights into thermal conditions at depth, as the vast majority of ocean temperature data comes from surface waters."