Declining underwater seagrass may harm corals, humans

Washington

Seagrass meadows can reduce bacterial exposure for corals and humans, according to scientists who warned that the most common coastal ecosystem on Earth are on a decline due to climate change.

"The seagrass appear to combat bacteria, and this is the first research to assess whether that coastal ecosystem can alleviate disease associated with marine organisms," said Joleah Lamb of Cornell University in the US.

"Global loss of seagrass meadows is estimated at seven per cent each year since 1990, he said.

"I hope these results will send a clear message to other regions of the world about the potential benefits that these ecosystems can have on human and marine health," Lamb added.

The group used Enterococcus assays, a standard of health risk levels for wastewater pollution in recreational waters, to see whether seagrass meadows influenced bacterial levels.

Water samples taken near the beaches exceeded exposure levels by a factor of 10.

The team found threefold lower levels of Enterococcus in seawater collected from within seagrass meadows.

"The genetic sequencing work pinpointed the kinds of bacteria — all in difficult, arduous conditions," said Drew Harvell, professor of the Cornell University.

"It showed exactly what was in the water. The beautiful oceanside water looked blue-green, but truly it was filled with dangerous pollution - some really bad stuff in the water close to shore," said Harvell.

While research is beginning to reveal the mechanisms driving bacterial-load reductions in these ecosystems, it is evident that an intact seagrass ecosystem — home to filter-feeders like bivalves, sponges, tunicates (marine invertebrates) — removes more bacteria from water.

As seagrass meadows and coral reefs are usually linked habitats, Lamb's team examined more than 8,000 reef-building corals for disease.

The researchers found lower levels — by twofold — of disease on reefs with adjacent seagrass beds than on reefs without nearby grasses.

"Millions of people rely on healthy coral reefs for food, income and cultural value," said Lamb.

Researchers agree that these findings are key to conserving seagrass ecosystems.

"Global loss of seagrass meadows is about 7 per cent each year since 1990," said Lamb.

"Hopefully this research will provide a clear message about the benefits of seagrasses for human and marine health that will resonate globally," he said.

Regions around the world promote aquaculture to help feed populations, as diseases for many ocean-dwelling plants and animals increase, Harvell said.

"Our goal is to stop measuring things dying and find solutions. Ecosystem services like seagrass meadow habitats are a solution to improve the health of people and the environment. Biodiversity is good for our health," he added.

The study was published in the journal Science. — PTI