Hungry ‘bugs and slugs’ keep seagrass healthy

Invertebrates like this isopod keep seagrass clean and healthy. (Credit: Pamela Reynolds)

Marine “bugs and slugs” make ideal houseguests for valuable seagrass ecosystems.

They gobble up algae that could smother the seagrass, which keeps the habitat clean and healthy, according to results from experiment spanning the Northern Hemisphere.

The study took place simultaneously at 15 sites across seven countries through a project called the Zostera Experimental Network, or ZEN, after the seagrass species Zostera marina.

“Our results show that small marine invertebrates are really important,” says project coordinator Pamela Reynolds, a postdoctoral scholar at the University of California, Davis, and the Virginia Institute of Marine Science, which led the study.

“They graze down seaweeds that might otherwise smother the seagrass,” she says. “It’s a really neat partnership—the animals get a home, and the seagrass stays clean. We found that the more diverse communities of these little algae-eating animals do a better job of keeping the seagrass clean and healthy.”

Threats to seagrass

Reynolds says the results support that comprehensive coastal management should consider how to maintain robust populations of animals in addition to managing for the more conspicuous effects of pollution and disturbance.

Seagrass meadows provide valuable fish nurseries and feeding grounds for birds, sea turtles, and manatees. They sequester carbon, and their root systems help bind and protect coastlines. Yet, they are declining worldwide due to a host of factors.

The researchers explored which of two known threats to seagrass has the greater impact on seagrass ecosystems: pollution from fertilizers or the loss of invertebrate species due, in part, to fishing.

Cut the fertilizer

To simulate nutrient pollution, the team members fertilized the seagrass similarly to how one would a lawn. Then they drove away small crustacean grazers by applying a chemical deterrent, simulating changes in the food web from fishing. On average, removing the grazers produced more algae than adding the fertilizer. Researchers at work in North Carolina.

“Our results provide rare large-scale confirmation of the importance of biodiversity to healthy ecosystems,” says Emmett Duffy, the study’s lead author and director of the Smithsonian’s Tennenbaum Marine Observatories Network.


“It’s widely understood that controlling algal overgrowth of seagrasses requires reducing fertilizer runoff, but it turns out that maintaining diverse populations of the bugs and slugs that clean these underwater plants is just as important.”

Ongoing work by the team seeks to understand how the diversity of seagrass animals and plants contributes to fish production, carbon storage, and other ecosystem services.

The study appears in Ecology Letters. Funding came from the National Science Foundation and local support from the 15 partner institutions.

Source: UC Davis