Urchin barren facts for kids
An urchin barren is a part of the ocean where sea urchins have eaten almost all the kelp plants. This changes a healthy kelp forest into an empty, desert-like area. When there are too many sea urchins, the fish, krill, and other animals that live in the kelp either die or move away. Urchin barrens are found in coastal areas of the Pacific Ocean.
Urchin barrens have been around for a long time. However, in the late 2010s, many more of these areas started appearing.
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Why Urchin Barrens Form
Scientists first noticed urchin barrens in the 1800s. This was when people hunted sea otters for their fur. So many sea otters were killed that they almost disappeared. Sea otters love to eat sea urchins. Without enough sea otters, the number of sea urchins grew very large.
Warm ocean currents can also affect how many sea urchins there are. In some places, kelp forests might turn into urchin barrens. Then, they can grow back later, depending on the ocean currents that year.
The Role of Starfish
Starfish also eat sea urchins. The sunflower sea star is the only animal that regularly eats the purple sea urchin. Even sea otters prefer to eat red sea urchins more than purple ones.
In 2013, a disease killed most of the starfish along the Pacific coast. This meant there were many more purple sea urchins left. One study showed that the number of purple sea urchins in a reef off the coast of Oregon grew by 10,000% between 2014 and 2019. These extra urchins ate or crowded out other sea creatures, like red abalone.
When purple sea urchins run out of food, they sometimes try to eat each other. Then, they become dormant, which means they go into a resting state, almost like sleeping. They do not try to reproduce, and their bodies shrink. This means they cannot be collected and sold for food.
How Climate Change Affects Kelp
Scientists say that warmer ocean water in the early 2010s made the bull kelp weaker. In 2016, a large area of warm water, called the "Blob," made the coast of California very warm. This warm water also made it easier for sea urchins to reproduce, so they had many more babies than usual.
A study showed that 90% of the bull kelp off the coast of California was killed in the late 2010s because of these changes.
Helping Kelp Forests Grow Back
Scientists have done experiments to see if other animals, like lobsters, would eat enough purple sea urchins to help the kelp forests recover. These animals helped a little, but not enough.
In areas where sea otters have returned, like the Juan de Fuca Strait, they ate enough sea urchins for the kelp forests to grow back. This shows how important sea otters are to the ocean's balance.
Some companies have hired divers to collect purple sea urchins. They take these urchins to special sea farms where they are fed until they are healthy. Then, they can be sold for people to eat.
Images for kids
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An urchin barren forming.
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Humans hunted sea otters for their skins in the past.
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