page_title: Urchin barren
section_title: Causes
hierarchical_section_title: Urchin barren / Causes
context_page_description: Urchin barrens are places in the ocean where sea urchins have eaten and killed so many kelp plants that they turned a kelp forest into something like a desert. This happens when there are too many sea urchins. The fish, krill and other animals that live in the kelp either die or leave. Urchin barrens occur in coastal areas of the Pacific Ocean.
  Urchin barrens had been forming for a long time, but in the second half of the 2010s, there were suddenly many more.
context_section_description: People first noticed urchin barrens in the 1800s when the sea otters were hunted for their fur. People killed so many sea otters that they almost went extinct. Sea otters like to eat sea urchins, so without sea otters to eat them, there were many, many sea urchins.
  Warm ocean currents also affect sea urchin populations. In some places, kelp forests turn into urchin barrens and then grow back depending on the currents that year.
  Starfish also eat sea urchins. The sunflower starfish is the only animal that regularly eats the purple sea urchin. Even sea otters like red sea urchins more. When a disease in 2013 killed most of the starfish on the Pacific coast, there were many more purple sea urchins left. One study showed that the number of purple sea urchins in one reef off the coast of Oregon increased 10,000% in the five years between 2014 and 2019. They either ate or crowded out the red abalone and red sea urchins that humans like to eat. The abalone fishery in California closed in 2018, a loss of US$44 million per year.
  When purple sea urchins run out of food, they try to eat each other, and then they become dormant, as if sleeping. They do not try to reproduce, so their gonads shrink. Because the gonads are the part of the urchin that humans like to eat, dormant purple sea urchins cannot be caught and sold for food.
caption: The sunflower sea star is the only animal that eats large numbers of purple sea urchins.
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