Japanese seaweed is welcome invader on US coasts: study

Miami (AFP) –


A kind of Japanese seaweed that is considered an invasive species in the United States is actually serving an important role in restoring barren and vulnerable coastlines, US researchers said Monday.

In many lagoons and estuaries of the North Atlantic, native seagrasses and oyster beds have been "severely reduced," due to global warming, pollution, disease and overharvesting, said the report in the Proceedings of the National Academy of Sciences.

In North Carolina, where the study took place, some 97 percent of seagrasses, 90 percent of oyster reefs and 12 percent of salt marshes have been lost relative to their historical extent.

In these mudflats, invasive Gracilaria vermiculophylla has been spreading, so researchers decided to analyze how it was affecting the ecosystem.

The Japanese seaweed is believed to have made it into North Carolina via the export of a kind of oyster -- known as the Pacific Oyster (Crassostrea gigas) -- from Japan.

Over a 10-month span, 48 large plots with different densities of Gracilaria were studied for changes in vital services to the environment, including soil stabilization and erosion control, storm surge and flood protection, biodiversity, food production, and habitat for economically important seafood species.

They found the invasive plants helped biodiversity in many ways, particularly by boosting habitat for young shrimp, crab and fish.

"We did not find a significant relationship between Gracilaria cover and sediment stabilization, a process that underpins erosion control," said the report.

Overall, the picture was positive, and suggests invasive underwater weeds may help, not harm native species and ecosystems, said co-author Brian Silliman, associate professor of Marine Conservation Biology at Duke University's Nicholas School of the Environment.

"Our experimental study shows for the first time that this can be the case," he said.

Still, millions of dollars are spent annually to eradicate or contain a host of invasive species all over the world in the name of conservation.

"Conservation and restoration practitioners must now begin the hard conversation about changing their black-and-white picture of invasive species impacts," Silliman said.

The problem is not unique to North Carolina, but extends globally.

Recent studies have found that as many as 20 percent of coral reefs, 30 percent of seagrasses, 45 percent of salt marshes and 90 percent of oyster reefs have been lost worldwide, according to background information in the article.

"With the progressive decline of coastal habitats worldwide, our findings suggest it's better to have a non-native habitat than no habitat at all," said lead author Aaron Ramus, a post-doctoral student at University of North Caroline, Wilmington.

"There's a good chance that many invaders don't have the negative effects that we often think they do."