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Sea Urchins vs Kelp Forests

Updated: Jan 8

Ecosystems are intricate, complex systems containing a plethora of organisms, all of which hold an important role in sustaining a viable habitat. A healthy ecosystem is characterized by a balance between its biotic (living) and abiotic (nonliving) components.

However, when the delicate balance of an ecosystem is disrupted by human interference or natural disasters, it is extremely challenging for that ecosystem to reach its original state of balance and stability again on its own. Although humans are one of the major contributors to ecosystem disruption, we also have the ability to help restore ecosystems to their original states.

Sea urchins play a vital role in ocean ecosystems and their importance is underestimated by many. This blog will explore the purple sea urchin, also known as Strongylocentrotus Purpuratus, commonly found along the coast of California.


What are Sea Urchins?

Sea urchins are a part of the phylum echinodermata group which includes sea stars, sea cucumbers, and sea lilies. They are marine organisms that live in the intertidal zones of kelp forests, often found nestled in crevices between rocks.

It is difficult to identify sea urchins based solely on their color because different species of sea urchins come in different colors. However, all of them can be identified by their spherical shape and spiky outer layer. All sea urchins have 5-point symmetry, similar to starfish.

As disgusting as it may seem, some countries consider the gonads (reproductive organs) of certain species of sea urchins a delicacy. Although you won’t find many seafood restaurants with sea urchins on the menu in the US, they are a rather common dish in Mediterranean and East Asian countries. Some seafood enthusiasts complain that sea urchins taste like kelp or seaweed because that is their main food source.

Sea urchins play an important role in aquatic ecosystems because organisms such as sea stars and sea otters rely on them for food. All ecosystems are delicate and even a minor disruption can have disastrous consequences. Read on to learn more about the current sea urchin problem and how it’s affecting aquatic ecosystems in all of Earth’s oceans.

The Urchin Problem

Starting in 2014, the purple sea urchin population along the coast of California has increased rapidly. Sea urchins generally reside in kelp forests because kelp is their main source of food. However, recently they’ve been discovered in urchin barrens across the coast the California.

Urchin barrens are barren places along the sea floor where kelp forests stood before sea urchins invaded and consumed all of the kelp. These barrens usually consist of thousands of sea urchins heavily concentrated in one place with little to no kelp left.

Once these sea urchins have exhausted the kelp supply in a particular location, they migrate to new places along the seafloor in search of a new kelp forest to inhabit. As sea urchin populations grow rapidly, the number of kelp forests left decreases drastically. Other organisms who rely on kelp forests for food or shelter are slowly dying out.

As kelp forests grow more and more scarce, sea urchins will even feed on kelp that is only just starting to grow. This prevents the growth of new kelp forests in the future which would help replenish the supply of kelp that sea urchins originally consumed. The regeneration of kelp forests will be almost impossible if sea urchins continue consuming kelp at this rate.

Population Dynamics

"The Blob"

You may be wondering, how did the sea urchin population grow so rapidly over such a short period of time? The problem began when a large mass of warm water known as “the blob” reached the shores of California. Kelp forests are more adapted to survive in warm waters than other similar sea plants. Because of this, many organisms moved to kelp forests when their previous habitats started to decline as a result of the blob.

This put an huge amount of strain on kelp forests which were housing more organisms than ever before. Kelp forests began to shrink when sea urchins flocked to them searching for a new food source. Humans are mostly to blame for these events as ocean waters are warming because of our excessive greenhouse gas emissions.

Climate Change

It is well known that climate change and pollution affect ecosystems worldwide. But, how does this account for the rapid influx of sea urchins to the coast of California in recent years?

According to Science Daily, kelp forests, although more adapted to higher temperatures than other ocean plants, have more difficulty growing at high temperatures. With the recent increase in greenhouse gas emissions from large factories and vehicles, climate change is accelerating at an unprecedented rate and Earth is warming rapidly, putting our precious kelp forests at risk.

Many sea urchins have migrated to California in recent years because they have exhausted their kelp supply elsewhere and are looking for new food sources. Unfortunately, kelp forests can’t keep up with the insatiable hunger of the sea urchins. Climate change inhibits the growth of kelp forests, leaving little to no chance for regrowth after sea urchins consume the entire forest.

Natural Predators

Sea stars, specifically the sunflower sea star, prey on sea urchins to survive. During the past couple of years, sea star populations began to decline. For any ecosystem, when predator populations decline, prey populations increase because there are less organisms hunting them.

The culprit of these sea star’s deaths was a sea star wasting disease in which they were bleached of color, and their limbs began to break off which eventually led to death. While the origins of this disease are still not certain according to NOAA, there is speculation that low pH and pollution could have contributed to the growth and spread of the disease.

Sea otters are another predator of sea urchins. This is mostly because sea otters and sea urchins both live in kelp forests. Sea otters that don’t live in kelp forests have other sources of food but sea otters in these forests rely on them for survival.

Potential Solutions

Large Operations

While this problem may seem hopeless, federal and state environmental organizations have been taking action to address the sea urchin issue. Sea urchins are being collected in large quantities from urchin barrens and sold to restaurant owners who want to get their hands on the hard-to-come-by delicacies. Some of these sea urchins are fed kelp until their gonads grow to a sufficient size and are harvested for sale.

Sustainable Living

While large corporations can do more to solve this issue than we can, there are still various things we can do to help save our kelp forests. Always be mindful of your contribution to global warming. A common misconception about reducing your personal carbon footprint is that it has to be all or nothing, but that’s not true.

It would be unreasonable to expect everyone to completely switch to renewable energy. Even the small steps count. Next time you leave the house turn off the heater and the lights to conserve energy. Try carpooling with a friend to reduce your carbon dioxide emissions! If everyone makes a small sacrifice for the good of the environment, future generations will have the chance to enjoy the Earth we have today.



All ecosystems are incredibly sensitive to changes in population because all organisms rely on each other for food or shelter. The rapid growth of the sea urchin population along the coast of California has harmed kelp forests beyond repair and destroyed aquatic ecosystems.

Their rapid increase in population can be attributed to migration driven by climate change and a large marine heatwave in California from 2012–2014 called “the blob.” Sea urchins razed kelp forests to the ground with their hunger and created urchin barrens. When this occurred, the organisms that called kelp forests home were left without a proper habitat or food source.

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Author: Ann Catechis

Editor: Emma Mazzotta


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