This sea star has a craving for coral.

With a puffy and prickly body, the spiny star (Hippasteria sp.) is easy to spot on the deep seafloor. These stars roam the seafloor searching for a delicious dinner. And a hungry Hippasteria can be quite particular when it comes to feeding. For some, sea pens or anemones are their sole preference. Here in our backyard, spiny stars seek out prey that is particularly prevalent in the Monterey Bay and beyond: deep-sea corals.

While some corals have evolved protective stinging sweeper tentacles to deter hungry predators, spiny stars are determined in their quest for a nutritious feast. They use tiny tube feet to scale a towering coral. When they find the right spot, usually starting from the coral’s base, they wrap their arms to hang on tight, then extrude their stomach out of their mouth to devour the juicy coral polyps. 

Hippasteria are important in restructuring the habitats where they live. As they leave dead coral skeletons behind, homes for new animals are created. This natural turnover keeps the community healthy and helps foster diversity among the fishes and invertebrates that live there. 

Animals that live deep in the ocean thrive in cold water and high salinity. Changes in climate at the surface ripple down to the depths below. Warmer and more acidic waters put deep-sea corals—and the animals that depend on them for food and shelter—at risk. Will animals like Hippasteria withstand the loss of these corals? Our researchers are working hard to find out. We have deployed advanced technology to study the coral gardens at a rocky ridge off the Big Sur coast. Cameras and other instruments designed by MBARI engineers are helping us learn about the dynamic community that lives on and around deep-sea corals.

Back in the lab, spiny stars collected with our robotic submersibles have helped our collaborators at the Smithsonian’s National Museum of Natural History better understand the relationships among Hippasteria species around the globe. DNA analysis revealed that what were once thought to be a dozen distinct species were a single global species, Hippasteria phrygiana.

During an expedition to Pioneer Seamount, offshore of San Francisco, we spotted a few smaller spiny stars with a ghostly white color. Our Smithsonian collaborators determined that these were a previously unknown species that they named Hippasteria tiburoni in honor of our retired remotely operated vehicle Tiburon. Our dives at seamounts along the West Coast also revealed two new species of related sea stars with a similar appetite for corals—Evoplosoma claguei and Evoplosoma voratus.

Studying the animals of the deep is increasingly urgent. Overfishing, pollution, and climate change all threaten the deep ocean. What we learn in the field and in the lab improves our baseline understanding of deep-sea communities so we can assess and track ongoing human impacts on the animals and habitats far beneath the ocean’s surface.