Bottom trawling is killing the seafloor and collapsing deep sea biodiversity

(NaturalNews) The method of industrial fishing known as "bottom trawling" is destroying the biodiversity of the ocean floor, possibly forever, according to a study conducted by researchers from the Polytechnic University of Marche, Italy, the Autonomous University of Barcelona, Spain, and the Institute of Marine Sciences (also in Barcelona), and published in the journal Proceedings of the National Academy of Sciences.

The researchers compared the effects of bottom trawling to desertification or the loss of topsoil, noting that trawling reduces habitat quality so much that the ecology of the ocean floor may never recover.

"In the long run, it causes a steady loss of fine sediments, soft and rich in organic matter, leaving a more depleted and compacted seabed sediment surface that it is more difficult to be colonized again," researcher Jacobo Martin said.

Ocean food chain devastated

Bottom trawling -- which consists of dragging a net across the ocean floor and scooping up everything in its path -- is one of the most widely used fishing methods in the world, but it is also one of the major causes of seabed degradation. Although the practice originated in the 14th century, its use has exploded in the past 30 years, as new technology has made it possible to trawl to even greater depths than ever before.

In the new study, conducted in submarine canyons off the northeastern Catalan coast and following up on earlier work by the same scientists, researchers measured several markers of biological diversity, with a focus on tiny organisms known as meiofauna (life forms between 30 and 500 micrometers in size) living in marine sediments. The fishing grounds studied were about 500 meters in depth.

The researchers found that the constant stirring of sediment caused by repeated trawling led to 80 percent lower levels of meiofauna and 50 percent lower levels of biodiversity than in non-trawled areas.

This loss in meiofauna is particularly significant, as they form the base of the deep-sea food chain.

Researcher Pere Puig said that "the dragging of the gear on the seabed lifts and removes fine particles of sediment, yet also resuspends small organisms living in the sediment that constitute the base of the food chain at these depths."

The researchers found that the number of nematodes, the most common form of meiofauna at such depths, had decreased by 25 percent. In addition, the organic content of the sediment was 50 percent lower in trawled areas, and carbon degradation (a major ecological function of the deep sea floor) was reduced by 40 percent.

The deep sea bed plays such an important role in overall oceanic health that its destruction is comparable to the destruction of topsoil on land, the study notes.

"The fishing grounds are compared to agricultural fields... and may end up becoming barren if the constant loss of superficial sediment endures over time," researcher Pere Masque said.

Urgent action needed

Given the scale of damage found in the study, the researchers warned, immediate action is needed to implement sustainable deep-sea fishing practices.

The paper came only days after an even more severe warning from the inaugural session of the Deep Ocean Stewardship Initiative (DOSI) was published in the journal Science. The coalition of oceanography experts warned that the deep ocean is threatened by a boom in trawler fishing, oil and gas development, industrial-scale mining, waste disposal and land-based pollution.

The statement calls for international collaboration to sustainably manage deep ocean resources, many of which fall outside national boundaries.

"We humans don't have a great track record with stewardship of land and our coastal ocean," DOSI co-founder Dr. Lisa Levin said. "Hopefully, we can do a better job with the deep half of the planet."

"Future generations depend upon our actions," paper co-author Maria Baker said.

Sources for this article include:

http://www.eurekalert.org

http://www.sciencedaily.com

http://www.alphagalileo.org