Professor tussles with army of sea urchins to help fishermen

[Japan] A university professor is on an unusual quest … to turn an invasion of tasteless sea urchins with withered gonads into a gravy train for struggling fishermen.

The creatures are creating a nuisance here in northeastern Japan for fishermen who rely on a healthy marine ecosystem as they struggle to recover from the 2011 tsunami that devastated the region.

Yukio Agatsuma, a professor of marine plant ecology at Tohoku University, has opted to kill two birds with one stone: reduce the population of particular sea urchins that exploded after the 2011 tsunami washed away their predators, while also putting cash in the pockets of fishermen who have to spend time removing the invaders from the sea.

And it’s not quite so simple as to just eat them–because they don’t taste that great.

In the autumn of 2013, the sudden outbreak of “kita murasaki uni” (northern purple sea urchins), or, if you prefer, strongylocentrotus nudus, occurred in the Shizugawa bay of Minami-Sanriku, according to Agatsuma.

In highly concentrated areas, 20 urchins can be found huddling in a 1-meter square area. Viewed from a boat, the seabed appears black in places.

The towering tsunami not only destroyed the homes of Minami-Sanriku residents but also the habitats of marine animals in the bay. The population of crabs and starfish that used to live here and feed on the sea urchins dwindled.

Many of the sea urchins were also washed away, but as a single sea urchin can spawn up to 10 million eggs in one go it wasn’t such a big deal for the species.

Agatsuma believes sea urchins born half a year on from the tsunami in March 2011 matured safely in deeper waters, and then stormed back en masse to the bay in 2013.

A similar phenomenon also occurred in Miyagi’s Kesennuma and Iwate Prefecture’s Kamaishi.

Strongylocentrotus nudus is usually considered a delicacy, but the urchins that grew up in the post-tsunami baby boom are not.

They are generally malnourished as they had to fight for their staple seaweed, and their “meat,” a tasty reproductive organ, was emaciated. They get so hungry that they also feed on fish carcasses out of desperation, which makes their meat bitter and unsavory.

“Arame” seaweed has also been attacked by the avaricious urchins. The seaweed colonies were damaged by the tsunami, but recovered … until the sea urchins began eating them.

The seaweed is an important part of the ecosystem in the shallow water as it provides a habitat and a source of food for other creatures. To protect the local arame seaweed, the sea urchin population needs to be controlled, but it takes time and manpower.

Agatsuma thought that if the malnourished urchins could be sold, collecting them would be worthwhile for fishermen while also helping the ecosystem in their fishing grounds.

In February 2014, he began culturing the unsavory sea urchins.

He gathered 320 of them with help from local fishermen, put them in cages and plopped them back into the sea. The urchins happily gobbled up “kombu” seaweed Agatsuma fed them rather than feasting on the local aquatic vegetation.

When he checked their meat three months later, the amino acid component that contributes to the tastiness of their gonads had increased, and the chemical component for the bitterness had decreased.

They also smelled better.

In 2015 and 2016, he cultured 500 urchins each year to gauge the best time for producing the most delicious urchins.

This year, Agatsuma is attempting to raise the urchins in water tanks on land as they are less susceptible to climate condition, and studying the taste variations by feeding them not just konbu but other kinds of seaweed.

Agatsuma said he is aiming to produce “sea urchins that taste better than a wild catch.”


Photo: Sea urchins dine on “arame” seaweed in the Shizugawa bay of Minami-Sanriku, Miyagi Prefecture. (Provided by Yukio Agatsuma)

View original article at: Professor tussles with army of sea urchins to help fishermen


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