Seagrass Can Work as a Sanitation Service

Several years ago, a spate of illnesses hit the members of Joleah Lamb’s dive team. Lamb, a marine ecologist at the University of California, Irvine, was investigating coral disease in Indonesia with her colleagues when they were afflicted by dysentery, a type of gastroenteritis. This common ailment can be caused by ingesting water contaminated with bacterial pathogens such as Enterococcus. Though symptoms are usually mild, gastroenteritis can be fatal. Each year, gastroenteritis and related illnesses kill millions of people around the world—particularly children under the age of five.

Lamb and her colleagues’ experience led to a scientific discovery: the concentrations of Enterococcus pathogens that can cause gastroenteritis are lower in some parts of the ocean than in others. Notably, gastroenteritis-causing pathogens are less common among seagrass meadows.

In a recent study, a team led by Fortunato Ascioti, an ecologist at the University of Palermo in Italy, built on Lamb’s insight to estimate the global potential of seagrass as a coastal sanitation service. Ascioti’s effort, which was independent of Lamb’s work, found that if all seagrass meadows around the world provide this pathogen-reducing service, they could be responsible for a reduction of up to 24 million cases of gastroenteritis per year. The savings of seagrass sanitation on healthcare alone could be worth as much as US $74-million globally.

Ascioti explains the finding is a rough estimate of the sanitation potential of some seagrasses. There are more than 70 species of seagrasses, he says, and only a handful are known to have this effect. Based on current knowledge of those seagrass species, Ascioti and his team calculated that around eight million cases of gastroenteritis are likely being avoided annually.

Lamb, who was not part of the global estimate research team, says that when it comes to valuing seagrasses, these projections of the potential reduction in gastroenteritis per year are conservative. “I would say this is just an estimate of the value of the seagrass sanitation service reducing pathogens for just one type of illness,” she says.

This is because different seagrasses target different pathogens. Lamb’s study identified three seagrass species, Enhalus acoroides, Thalassia hemprichii, and Cymodocea rotundata, that are effective against gastroenteritis-causing Enterococcus bacteria. But previous research has shown that the Mediterranean endemic seagrass Posidonia oceanica can reduce the concentration of Escherichia coli, while the temperate water–dwelling Zostera marina helps reduce pathogens in the Vibrio genus.

Seagrasses can also help clean the water for other marine species, including those harvested as seafood.

Whether society can tap into this sanitary power by planting seagrass meadows is a complex question, Lamb says, because scientists aren’t entirely sure how seagrass does this job.

“We don’t know, at least in the tropical systems, if [seagrasses] play complementary roles with each other, or if a single species can have that pathogen reduction effect,” Lamb says. Density of seagrass meadows may also play an important role, she notes. Further research is needed to understand if this service is retained in replanted meadows.

Yet with human populations living in coastal areas set to grow, mitigating disease-causing pathogens will only become more important.

This article is from Hakai Magazine, an online publication about science and society in coastal ecosystems. Read more stories like this at hakaimagazine.com.

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