Purple sea urchins and California's kelp forests
Sydney Hollingsworth. 04/16/2021
The waters along the Californian coast contain a rich variety of marine life. From seals to colorful crustaceans to whales, thousands of species make their homes in the reefs and kelp forests near the rocky beaches of North America.
Unfortunately, a common theme among delicately balanced ecosystems around the world is the threat of destruction posed by human activities, and California’s marine landscape is no exception. The towering underwater forests, composed of 60 feet tall bull kelp stems, are facing annihilation at the hands of the purple sea urchin population, which has swung wildly out of control and decimated 95% of California’s kelp forests since 2014.
Unlike most other situations where an organism introduced by humans outcompetes an entire ecosystem, the purple sea urchin is actually native to California, not an invasive species. This means there is still hope that balance can be reestablished without the removal of the purple sea urchin entirely.
The emergence of this problem can be traced all the way back to the 1800s, when sea otters, a main predator of the purple sea urchin, were hunted nearly to extinction for their waterproof skins. More recently, a toxic algal bloom in 2011 killed off many marine species, including the sunflower sea star. Additionally, the sea stars were threatened further in 2013 by a mysterious “sea star wasting syndrome”, which causes the stars to decay and lose their limbs, eventually resulting in death. With its 20 limbs and large diameter of up to one meter, the sunflower sea star was once a fearsome predator of the purple sea urchin but is currently considered critically endangered.
Another factor contributing to the declining bull kelp population is global warming. Increasingly common heat waves since 2014 mean a less nutrient-rich water supply for all marine life, including the annually released bull kelp spores. The warmer temperatures may also worsen the effects of sea star wasting syndrome.
Together, these events have resulted in less than favorable conditions for the keystone species that is the bull kelp and created a virtually predator-free environment for the purple sea urchin. Urchin barrens are vast areas where thick kelp forests have been completely replaced by sea urchins. The hordes of spikey bodies cover the seafloor with what has been called a “purple carpet”, as the healthy number of 2 urchins per square meter has been replaced by 70 individuals in the same space.
According to the California Department of Fish and Wildlife (CDFW), if the bull kelp spores cannot set for more than three years in a row, the forests could disappear completely, and take countless species with them. Besides providing food and shelter for marine life, bull kelp also help control wave activity and reduce coastal erosion. Thus, its disappearance would endanger marine life, as well as harm local commercial fishers and economies.
Luckily, marine biologists believe this problem is fixable, and with the right efforts, the purple sea urchin population can be regulated and bull kelp forests can be returned to their former glory.
The main plan of many organizations involved in the bull kelp conservation effort is to remove purple sea urchins by hand until their natural predators can be rehabilitated. Purple sea urchins are edible, and quite delicious when prepared correctly. Urchin removal projects often obtain funding from selling harvested urchins to restaurants.
However, one problem with this plan is that due to their abundance, most purple urchins are underfed and far too small to compare to the more favorable red sea urchin, which is considerably larger. To find a solution to this, researchers at the Moss Landing Marine Laboratories Center of Aquaculture tried feeding captured purple urchins red algae, which helped them grow to market size in just eight weeks. This means purple sea urchins can be captured, fed, and sold to restaurants, all while giving the bull kelp forests a chance to grow back.
The second-largest setback purple sea urchin harvesting groups have encountered is that sea urchin is not a very popular dish, particularly in California. Some organizations, such as Urchinomics, a Norway-based company that faces a similar problem, ship their urchins to Japan, where urchin gonads, called uni, make a popular dish that tastes similar to the oyster.
However, shipping to international markets does not even start to cover all the purple sea urchins that must be removed to restore California’s marine ecosystem. Without local markets, the urchins will end up as compost, and conservation efforts will lose funding opportunities to continue their projects.
Though the removal of hundreds of millions of purple sea urchins may seem like a substantial feat, most researchers and volunteers agree that it is very plausible if we act soon. In addition, helping restore California’s kelp forests doesn’t have to feel like a chore; trying new foods and supporting small restaurants can benefit everyone involved.
With so many crises beyond the control of individuals, especially regarding the current biodiversity crisis, it’s always good to hear there is something you, personally, can do. Bull kelp is essential to the health of California’s wildlife; managing the purple sea urchin population can directly help over 700 species that rely on kelp forests and be fun, too.
Cover Photo: (Katie Sowul / California Department of Fish and Wildlife)
