Massive 24-Armed Sea Stars Could Bring Back Kelp Forests

Newswise — Marine biologists discovered that reintroducing sunflower sea stars could help restore kelp forests.

Why this is important:

• Healthy kelp forests are hotspots for marine biodiversity, but they now occupy just a fraction of their former range along the west coast of North America.
• They’ve been stressed by warming coastal waters and overgrazed by sea urchins.
• Sunflower sea stars—up to a meter across, with as many as 24 arms—are one of the main predators of sea urchins. But they’ve been nearly wiped out by sea star wasting disease, possibly contributing to the urchin boom.
• A new study suggests reintroducing sunflower sea stars could help restore kelp forests.
• The team, led by Aaron Galloway, a researcher at the University of Oregon’s Oregon Institute of Marine Biology, published the findings in Proceedings of the Royal Society B on February 22.

How it works:

• The average sunflower sea star can munch through almost 5 urchins in a week, the study showed.
• If sunflower sea stars returned to their former habitats, they could help keep hungry urchin populations in check—and possibly help restore kelp forests.
• “We show that these very large-scale sea urchin barrens probably couldn't have developed in the presence of sunflower sea stars,” also known as Pychnopodia helianthoides, Galloway said. “Our findings indicate that if Pychnopodia recovers, it'll suppress these urchin barriers and help the kelp forest recover.”
• The team collected the specimens at Friday Harbor Laboratories in Washington state.

Background

• Sunflower sea stars were once a vital part of kelp forests habitats. Alongside sea otters, they helped keep sea urchin populations in check. But sea otters were hunted to near-extinction in the 1700s and 1800s, and now occupy only a tiny fraction of their former range.
• Over the past decade, sea star wasting disease wiped out almost all the sunflower sea stars in Oregon and Washington.
• In warmer waters without many predators, urchin populations have exploded and devoured the kelp.
• Over time, the habitat has turned into a barren expanse of spiky urchins. Hotter oceans have also stressed kelp directly, making it even harder for the ecosystem to bounce back.
• “Once otters were gone, Pychnopodia were still here. So, the fact that 90 percent of them died off was huge,” Galloway said. “We’ve had an unfortunate pile of conditions that have been very bad for kelp forests. It all comes back to climate change that drives all this.
• The Galloway Lab: https://oimb.uoregon.edu/?faculty=aaron-galloway  
• Sarah Gravem, Oregon State University: https://ib.oregonstate.edu/directory/sarah-gravem

Resources:

• Link to study (live after 12:05 PT Feb. 22): https://royalsocietypublishing.org/doi/10.1098/rspb.2022.1897
• Oregon Institute of Marine Biology: https://oimb.uoregon.edu/