Hannah Miller, Explorer-in-Training, NOAA Ocean Exploration
During Dive 11 of the 2021 North Atlantic Stepping Stones expedition, remotely operated vehicle (ROV) Deep Discoverer encountered this sea star feeding on a stalk of coral. Belonging to the family Goniasteridae, this sea star’s scientific name is Sthenaster emmae, and it lives in deepwater environments. However, at 1,219 meters (4,000 feet), this is the deepest location the Sthenaster emmae has been recorded, according to National Museum of Natural History scientist Chris Mah, who observed this spectacular creature! This sea star is known as a “corallivore,” or a coral predator, and it feeds on the coral’s polyps by extending its stomach from its mouth onto the coral to digest the animal’s tissue. This stripping of polyps is a process known as “denuding.”
In this clip, the whip coral, belonging to the primnoid genus Calyptophora, is observed with the Sthenaster sea star firmly wrapped around it, yet the coral’s polyps and tissue still appear to be present. The lack of denuded polyps suggests the sea star has only recently begun munching down on the coral stalk. Further research is needed to determine how much time sea stars spend feeding on a single stalk of coral; the metabolism of deep-sea creatures is rather slow in comparison to shallow-water organisms, so these sea stars might spend anywhere from a few weeks to years chowing down on the same piece of coral.
Sea stars are important predators, as their diet largely influences deep-sea ecosystem activity and diversity. When sea stars devour coral tissue, the coral’s skeletons can become habitats for other organisms to live in, or, or around. Sthenaster acts as a “keystone” species due to its effect of changing ecosystem dynamics within its environment. Interactions between this deep-sea predator and its coral prey still require research and observation, which demonstrates just how little we know about these extraordinary creatures.
Published August 4, 2021