May 31, 2024 - News

Rise in sea urchins threatens Oregon's gray whale

An aerial photo showing a kelp field with a gray whale bursting air from its blow hole.

A gray whale forages for food off the coast of Oregon. Photo: Courtesy of Oregon State University

A drastic increase in sea urchins off the coast of southern Oregon has been depleting food resources for migrating gray whales for years, causing the marine mammal to sometimes avoid the area entirely, a new study finds.

Why it matters: Gray whales are essential to oceans, keeping prey populations in balance and providing nutrients to the water. Their prolonged absence could have negative impacts over time.

The latest: A team of researchers from Oregon State University's Marine Mammal Institute found an indirect link between kelp forests damaged by sea urchins overfeeding and the loss of zooplankton populations, the gray whale's main food source.

What they did: In 2015, researchers began dropping several GoPro cameras in locations along nearshore reef habitats — concentrated largely in Port Orford — to monitor gray whale foraging behavior.

  • Three years after setting up the cameras, they began to notice "dramatic images" of hundreds of purple sea urchins covering dead kelp stalks and other parts of the reef, Lisa Hildebrand, the study's lead author, told Axios.
  • Researchers then began developing a method to count urchin populations daily and gathered zooplankton samples by kayak for monitoring.

Context: Sea urchins don't have many natural predators — and in Oregon the species has none.

  • Sea otters are locally extinct due to excessive fur trapping in the 19th century, and several marine heatwaves in the Pacific Ocean exacerbated an existing sunflower sea star pandemic — all leading to an explosion in sea urchins.

What they found: When urchin populations are left unchecked, they decimate kelp forests, where zooplankton and mysid shrimp live.

  • In the last six years, Hildebrand said she's observed fewer gray whales feeding in the area — they're either avoiding the region entirely or only staying for a short time.
  • The ones who stopped on their migration to the Arctic had poor body conditions overall, too, potentially due to poor diet.

Threat level: "If this is happening at a large spatial scale it could have big implications for their overall health and reproduction," Hildebrand said.

The bottom line: It's not all doom and gloom. Last year, OSU researchers noticed some positive signs: less sea urchin coverage at some of its stations, healthier kelp, an increase in zooplankton and a slight uptick in gray whales.

  • "That's the good thing about these ecosystems, they are resilient," Hildebrand said.
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