Sea urchins are overwhelming parts of the ocean. Could turning them into sushi be the solution?

Spiky, voracious and multiplying at an alarming rate, sea urchins are destroying marine ecosystems around the world. The solution? Eat them, according to one company.

Populations of purple sea urchins in particular – a hardy kelp-eating species – have exploded in recent years as an out-of-sync marine ecosystem has failed to keep them in check.

Munching their way through kelp forests from California to Norway, urchins leave vast expanses of desolate ocean floor – known as urchin barrens – in their wake. Not only are these kelp forests an important home for marine life, they are also crucial in our battle against climate change, capturing and storing carbon dioxide.

Urchinomics wants to turn this environmental challenge into an opportunity. By gathering urchins from the seabed and feeding them with sustainably harvested seaweed, founder Brian Tsuyoshi Takeda believes he can create a flavour-packed product that high-end restaurants will buy. Urchin roe has a rich savoury flavour and is seen as a delicacy, often served as sushi.

Once an area is cleared of urchins, rapidly growing kelp forests can return in as little as three months.

A vanishing ecosystem

One study estimates that plagues of purple sea urchins have caused a 90% reduction in a particular variety – bull kelp – along a 350 kilometre stretch of California coastline. This has in turn triggered the rapid decline of the local red abalone – a type of sea snail – and red sea urchin populations, both of which had multimillion-dollar fishing industries attached to them.

The problem is once sea urchins have run out of food to eat they can effectively go into stasis, surviving for years without eating, and so urchin barrens can last for years. But these starved urchins shrivel up inside their shells and have no economic value for food.

So-called urchin “ranching” may provide a solution by giving an economic incentive to remove the destructive creatures. But to have a real impact, the urchins will have to be all but eradicated.

A number of factors are thought to have contributed to growing urchin populations around the world, including a dearth of predators because of disease among the sea star population. This, along with factors like warming sea waters and pollution, means kelp forests are now under threat worldwide. They are disappearing at different rates around the world, but globally the decline is around 2% a year.

This is important because studies have shown that kelp and seaweed may have a more crucial role to play in climate change than we previously thought. Saltwater plants, particularly mangroves and seagrasses, can take up much more carbon dioxide from the atmosphere than land-based plants can. These “blue carbon” ecosystems not only take up carbon as the plants grow, but as leaves are shed and fall to the seabed this carbon is sequestered in the surrounding soil.

But despite these benefits, such ecosystems are under great threat. Tidal marshes and seagrass meadows and mangroves are all shrinking year-on-year. And in the past 50 years, it is estimated around 30-50% of mangroves have been lost globally.

Experts estimate that the carbon dioxide being released annually from degraded coastal ecosystems is equivalent to around a fifth of emissions from tropical deforestation globally.