Species already threatened by pollution and habitat depletion
The sea cucumber (Holothuria edulis) plays an important role in the oceans, despite resembling a burnt hot dog. A new study by the California Academy of Sciences investigated the sea cucumber’s role in the marine ecosystem in Okinawa as well as their vulnerability to environmental stress and overfishing.
Publishing their findings in the journal Conservation Genetics, the team called for better fisheries management and stronger protection for the sea cucumber.
“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,” said Dr Iria Fernandez-Silva, an Academy postdoctoral research fellow.
Sea cucumbers are marine invertebrates found in a myriad of shapes, sizes and colours. To date, there are more than 1,500 different kinds worldwide. Describing them as “superstar ocean cleaners”, Dr Fernandez-Silva admitted that it was easy to underestimate them, as they “looked goofy, move slowly, and barf up their guts when startled.”
Sometimes known as the vacuum cleaners of the sea, sea cucumbers use their feeding tentacles to shove sand and rubble through its digestive system, so as to absorb nutrients from the dead plant and animal matter on the seabed. They subsequently expel clean and oxygenated sand in their wake.
Marine ecosystems rely on sea cucumbers for this “cleaning service”. Without them, an excessive amount of detritus would be left on the seabed and this could negatively impact plants and animals, and lower the health of the ecosystem.
In East Asia, rising consumer demand for sea cucumbers in food and medicine has led to increased fishing for them worldwide. Already having to deal with pollution and habitat destruction, overfishing may be the factor that pushes them into extinction. Currently, at least 16 species of sea cucumbers are already listed as “threatened with extinction” in the International Union for Conservation of Nature's Red List.
In the course of their research, Dr Fernandez-Silva and her team travelled around Okinawa to investigate the genetic diversity of the different populations of sea cucumber. Genetic diversity is essential in determining whether a specific population can survive, as organisms lacking in this are susceptible to threats like diseases.
“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,” said Dr Fernandez-Silva.
The researchers are currently studying different sea cucumber species in southern Japan. So far, their preliminary results have shown similar links between polluted environments and low population diversity.
Further Information: www.calacademy.org
Link to study: link.springer.com/article/10.1007/s10592-016-0823-8