A certain sea cucumber may just look like a burnt hotdog, but it plays a huge role in ocean ecosystems. Now, a new genetic study reveals this important role and also shows that it may be extremely vulnerable to environmental stress and overfishing.
The sea cucumber in question is called Holothuria edulis. Growing to about the size of a ruler, it appears to be a reddish color with black spots along its back. Like other sea cucumbers, it's a soft-bodied marine invertebrate.
"It's easy to underestimate the sea cucumber," said Iria Fernandez-Silva, one of the researchers. "Sea cucumbers look goofy, move slowly, and barf up their guts when startled, but these invertebrates are superstar ocean cleaners that are hugely important to marine ecosystems. Our study looks into the genetics behind the economically-important species Holothuria edulis so we can understand the pressures they face and help protect threatened sea cucumbers globally."
The sea cucumber H. edulis helps clean seafloors and coral reefs during the nighttime hours. It moves slowly across the seafloor, using feed tentacles to shove sand and rubble through its digestive system as it moves, absorbing nutrients from detritus. It then expels cleaner, oxygenated sand in its wake.
With that said, there has recently been a rapid rise in East Asia's demand for sea cucumbers for both food and medicinal properties. This has increased fishing pressures in many parts of the world, which may be bad news for these particular sea cucumbers. Already, populations of Holothuria whitmaei and H. scabra, which were once common in the Indian and Pacific Oceans, have declined 60 to 90 percent in their traditional ranges.
In this latest study, the researchers compared H. edulis population genetic diversity. This is particularly important to note, since genetic diversity can play a major role when it comes to population survival.
"The data tells a story," Fernandez-Silva said. "We saw low genetic diversity in some sea cucumber populations along Okinawa's eastern coastline, where water is polluted by nearby industry, runoff, and coastal development. In contrast, populations in more pristine sites on the island's west coast were more genetically diverse. Since populations appeared disconnected from one another, we can predict that overfishing might be the last straw for vulnerable sea cucumber populations ill-equipped for a comeback."
The new findings are important when it comes to understanding how these cucumbers are impacted by fisheries. More specifically, it shows that measures will have to be taken in order to preserve these species, which play such an important ecological role in oceanic systems.
The findings are published in the March 2016 journal Conservation Genetics.
