The “golden orb” that stumped NOAA’s deep-sea team in 2023 is the discarded base of a giant deep-sea anemone, according to a preprint posted to bioRxiv on April 21 and a NOAA release the next day.
The orb turned up on Aug. 30, 2023, on Dive 7 of the Seascape Alaska 5 expedition, when the remotely operated vehicle Deep Discoverer, working from NOAA Ship Okeanos Explorer, came across a gold, mound-shaped object with a hole in it, attached to a rock in the Gulf of Alaska at about 3,250 meters. A videographer first called it a “yellow hat,” NOAA Ocean Exploration said at the time, and the team’s guesses ran from a dead sponge to a coral to an egg casing.
There will be no ROV dive today as #Okeanos is in transit, but we plan to be back in the water this weekend. Meanwhile, peruse photos and video of the moment we came across this unidentified gold specimen: https://t.co/mKcs7ziGJq#seascapealaska #explore #ocean #Alaska #Okeanos pic.twitter.com/YN5I9uuB85
— NOAA Ocean Exploration (@oceanexplorer) September 8, 2023
The ROV’s suction sampler brought up a specimen a little over 10 centimeters (4 inches) across. Expedition coordinator Sam Candio said then that it was “biological in origin,” but the team could not say more until it reached a lab. It went to the Smithsonian’s National Museum of Natural History and NOAA Fisheries’ National Systematics Laboratory, which is housed at the museum.
The fibrous, layered tissue was packed with stinging cells. Abigail Reft of the lab identified them as spirocysts, a cell type found only in Hexacorallia, the group of cnidarians that includes sea anemones and stony corals. DNA barcoding was inconclusive, probably because the specimen carried DNA from other microscopic life. Whole-genome sequencing then confirmed animal DNA, with a large share of it from the giant anemone Relicanthus daphneae. Mitochondrial genomes from the orb and from a similar specimen collected in 2021 aboard Schmidt Ocean Institute’s RV Falkor were nearly identical to a known R. daphneae reference, NOAA said.
Allen Collins, a zoologist and director of the lab, said in the release: “We work on hundreds of different samples and I suspected that our routine processes would clarify the mystery.” The preprint, which lists Steven Auscavitch as first author and Collins as last, concludes that both specimens are remnant cuticles of the anemone. The authors also report cuticle from a R. daphneae collected in the Southern Ocean and photos of similar cuticles beneath living animals, and NOAA’s release points to a 2016 image of a living one off the Mariana Islands with a similar base.
What the work did not settle is what happened to the animal itself. NOAA says it is unclear whether the anemone that left the base behind died or moved away. The specimen is now catalogued as USNM_IZ_1699903 in the Smithsonian’s Invertebrate Zoology Collection.
