Sea Cucumbers Working Overtime

Diagram of a test project in Italy in which sea cucumbers cleaned up excrement from farmed mussels. GROSSO ET AL.

A topic that rarely, if ever, has made our pages, the sea cucumber’s moment in the spotlight has arrived:

A sea cucumber near Mindoro Island in the Philippines. IMAGEBROKER / ALAMY STOCK PHOTO

Are Sea Cucumbers a Cleanup Solution to Fish Farm Pollution?

Seafood farm operators are breeding and deploying sea cucumbers to vacuum up the massive amounts of fish waste that pose a major problem for their industry. It is part of an effort to redesign fish farms with multiple species so that they work more like natural ecosystems.

Sea bass at a fish farm in the Adriatic Sea off the coast of Slovenia. WATERFRAME / ALAMY STOCK PHOTO

Off the coast of the Hawaiian Island of Kauai, an underwater metropolis bustles. Sea turtles glide lazily through the surf while schools of fluorescent yellow butterflyfish weave between basketball-size sea urchins and sharp corals.

But Dave Anderson isn’t distracted by the otherworldly charm of the coral reef — he’s here on a mission. Around 70 feet below the surface, he finds his prize: a red sea cucumber.

Anderson plucks the spiky creature from the sea floor and, after a brief boat ride, delivers it to a glistening 18-acre pond at the Kauai Sea Farm, on the island’s southwest coast. Anderson is the production manager of this small commercial operation, which raises mullet, barracuda, tilapia, and other seafood for sale to local restaurants. But the sea cucumber in Anderson’s hands isn’t for eating — at least, not yet. Instead, this bottom-dwelling echinoderm is the newest member of the fish farm’s cleaning crew.

In the wild, sea cucumbers roam the sea floor, hoovering up sand and digesting the fish waste, algae, and other organic matter it contains. Sand they excrete is cleaner than sand they consume, which is why sea cucumbers are often called “the true vacuums of the sea floor,” says Arnold Rakaj, a marine biologist at the University of Rome.

Now, Anderson is letting these slimy organisms perform the same service at Kauai Sea Farm.

Aquaculture, or fish farming, now supplies more than half of the seafood consumed by humans globally, and the industry is projected to continue increasing to help feed growing populations. However, land-based and offshore fish farms face a big problem. With hundreds and sometimes thousands of fish swimming in the same net, pond, or tank, uneaten food, fish waste, and the bacteria it contains can build up to harmful levels, fueling outbreaks of bacterial diseases — such as fin rotmycobacteriosis, and bacterial gill disease — that kill millions of farmed fish each year.

The uneaten feed and waste contain nutrients like phosphorous and nitrogen that can accumulate and sink to the bottom, where they can fuel algal blooms or feed bacteria that suck oxygen from the water, creating “hypoxic” conditions that suffocate captive fish and kill native organisms that surround offshore farms. Recirculating systems that filter water and remove waste can be installed, but these structures require a lot of energy and maintenance, and they can cost upward of $200,000 on a large commercial aquaculture farm…

Read the whole article here.

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