Invasive Creatures Series – Part 1: The Tiny Marine Invader Destroying the Pacific’s Underwater Forests
Not every destructive force in the ocean is related to climate change. Meet the purple urchin (Strongylocentrotus purpuratus), a small creature with a massive impact on marine ecosystems along the Pacific coast. While climate change often takes the blame for ocean devastation, this native species is playing a destructive role all its own — turning lush kelp forests into lifeless underwater deserts.
At first glance, the purple urchin seems harmless — a spiny invertebrate quietly grazing on kelp and algae. However, with the disappearance of their natural predators, like the once-abundant sea otter and starfish, purple urchins have been reproducing unchecked. Their population has exploded, and the consequences are devastating. Purple urchins devour kelp forests, which are critical marine ecosystems that provide shelter and food for countless species, including fish, sea otters, and invertebrates. In a healthy ocean, these kelp forests are bustling with life. But where the purple urchin thrives, these underwater jungles are rapidly disappearing, replaced by what scientists call “urchin barrens.”
The reason for this devastation is simple: purple urchins are voracious eaters. They consume kelp at an astonishing rate, and with fewer predators to keep their numbers in check, they swarm the ocean floor, stripping kelp forests of their ability to regenerate. What’s left behind is a barren, lifeless landscape where little else can survive. For marine life that depends on kelp for habitat and food, these barrens represent a significant loss of biodiversity.
Origins of the Purple Urchin
Native to the rocky shores of the northeastern Pacific Ocean, from Alaska to Baja California, purple urchins have been a part of these ecosystems for thousands of years. They typically live in harmony with their surroundings, nestled among rocks and feeding on kelp and algae. In a balanced ecosystem, the purple urchin is just one of many marine herbivores, kept in check by predators like sea otters and starfish.
However, over the past few decades, significant changes have occurred. The populations of the urchins’ natural predators have plummeted, leading to an explosion in the number of purple urchins. The reasons are many, and not all are related to climate change. The fur trade of the 19th and 20th centuries decimated sea otter populations along the West Coast, removing a key predator from the marine food web. More recently, sea star wasting syndrome, a mysterious disease, has wiped out large numbers of starfish, another important predator of purple urchins.
With their natural predators in decline, purple urchins have begun to multiply unchecked, transforming marine ecosystems. Their population boom has resulted in the overgrazing of kelp forests, turning once vibrant, underwater jungles into barren wastelands known as “urchin barrens.”
While the purple urchin is native to these waters, their unchecked population growth is having devastating impacts on the very environments they once thrived in. Their origins are a reminder that even native species can become invasive when ecological balance is disrupted. As they feast on kelp at alarming rates, they not only strip away a vital food source for marine life but also erase the shelter and biodiversity that kelp forests provide.
This destruction isn’t solely a result of climate change, though warming ocean temperatures and other environmental pressures certainly play a role. It’s also a stark example of how human actions — like hunting sea otters and disrupting predator populations — can ripple through ecosystems, leading to unintended consequences.
