BOSTON, Mass. — Want a lawn that needs no mowing and helps the environment? Look no further than the coastal ocean. Meadows of underwater seagrasses lower the amounts of harmful bacteria that can be found in coastal waters. That’s the finding of a new study reported here, February 16, at the annual meeting of the American Association for the Advancement of Science.
The findings suggest that nurturing healthy seagrass beds throughout coastal waters could make the whole ecosystem healthier — from corals and fish to people.
Seagrasses are not truly grasses. They are flowering plants with long, narrow leaves. Found in shallow ocean waters, they can spread to form vast underwater lawns. These plants are “a marine powerhouse, almost equal to the rainforest,” says says Joleah Lamb, an author of the study. “They’re one of the largest stores of carbon in the ocean,” the ecologist says. “But they don’t get a lot of attention,” she adds. Lamb works at Cornell University, in Ithaca, N.Y.
It’s no secret that seagrasses improve water quality, says James Fourqurean. He’s a biologist at Florida International University in Miami and wasn’t involved in the research.
Scientists had known these plants are great at removing excess nitrogen and phosphorus from coastal waters. Those are nutrients that often run off of the land, polluting coastal waters. Now, it seems, seagrasses might take away harmful germs, too. Lamb’s team describes its findings in the February 17 Science.
What pointed them to the value of these plants
A few years ago, Lamb’s colleagues became ill while studying coral reefs in Indonesia. This archipelago nation straddles the Indian and Pacific oceans. When a city or village on one of the country’s thousands of islands dumps raw sewage into the ocean, shoreline bacteria populations can spike to dangerous levels. So dangerous, in fact, that they gave Lamb’s colleagues a serious diarrheal disease known as amoebic (Uh-MEE-bik) dysentery.
Water sampled close to the shore off of four small and densely populated islands there had 10 times as many Enterococcus bacteria as the U.S. Environmental Protection Agency deems an acceptable limit. These germs can cause illness in people. Moreover, their presence often signals the likelihood that other disease-causing germs also may be around. But water collected from tidal flats and coral reefs that hosted healthy seagrass beds had far lower levels of the bacteria than did similar sites fewer than 20 meters away. The difference between these sites? The germy ones had no seagrasses!
The water where seagrasses grew also had lower levels of numerous bacterial species that can make fish and marine invertebrates (such as corals) sick. And surveys of more than 8,000 coral heads showed that those growing next to or inside seagrass beds had fewer diseases than those growing farther away.
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It’s unclear how far from seagrass beds this cleaner water extends. But the plants’ benefits can ripple through the entire ecosystem, Lamb said at the news conference at the AAAS meeting. What’s more, healthier corals help protect nearby islands from erosion. And fish hosting fewer bacteria make a healthier source of food for people.
Lamb is now planning follow-up studies. She hopes they will show her exactly how these ocean plants clean the water. Like a shag carpet, seagrasses can trap small drifting particulates. This trapping can keep those pollutant bits from flowing on. The plants might ensnare bacteria in the same way, building up biofilms on their blades. Or, she suggests, the leaves could be giving off some germ-killing compounds.
The new findings are one more reason to conserve seagrasses, study coauthor Jeroen van de Water said at the meeting. He’s an ecologist at the Scientific Center of Monaco. Globally, seagrass beds are declining by 7 percent each year. Both pollution and habitat loss are contributing to their loss. Efforts are underway in some areas to restore these underwater lawns. Still, Lamb argues, “it’s better to stop what we’re doing to the meadows than to try to replant them.” Indeed, she points out: “It’s hard to start doing restoration projects if the environment isn’t exactly what the seagrass prefers.”
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annual Adjective for something that happens in every year. (in botany) A plant that lives only one year, so it usually has a showy flower and produces many seeds.
archipelago A group of islands, many times forming in an arc across a broad expanse of the oceans. The Hawaiian islands, the Aleutian islands and the more than 300 islands in the Republic of Fiji are good examples.
bacterial Having to do with bacteria, single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside animals.
biofilm A gooey community of different types of microbes that essentially glues itself to some solid surface. Living in a biofilm is one way microbes protect themselves from stressful agents (such as poisons) in their environment.
carbon The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.
coauthor One of a group (two or more people) who together had prepared a written work, such as a book, report or research paper. Not all coauthors may have contributed equally.
colleague Someone who works with another; a co-worker or team member.
compound (often used as a synonym for chemical) A compound is a substance formed from two or more chemical elements united in fixed proportions. For example, water is a compound made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O.
conserve To protect, as from loss or degradation.
coral Marine animals that often produce a hard and stony exoskeleton and tend to live on the exoskeletons of dead corals, called reefs.
ecology A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.
ecosystem A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra.
environment The sum of all of the things that exist around some organism or the process and the condition those things create for that organism or process. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature, humidity and placement of components in some electronics system or product.
Environmental Protection Agency (or EPA) An agency of the U.S. government that is charged with helping create a cleaner, safer and healthier environment in the United States. Created on Dec. 2, 1970, it reviews data on the possible toxicity of new chemicals (other than food or drugs, which are regulated by other agencies) before they are approved for sale and use. Where such chemicals may be toxic, it sets rules on how much may be used and where it may be used. It also sets limits on the release of pollution into the air, water or soil.
erosion (v. erode) The process that removes rock and soil from one spot on Earth’s surface, depositing it elsewhere. Erosion can be exceptionally fast or exceedingly slow. Causes of erosion include wind, water (including rainfall and floods), the scouring action of glaciers and the repeated cycles of freezing and thawing that occur in many areas of the world.
germ Any one-celled microorganism, such as a bacterium, fungal species or virus particle. Some germs cause disease. Others can promote the health of higher-order organisms, including birds and mammals. The health effects of most germs, however, remain unknown.
habitat The area or natural environment in which an animal or plant normally lives, such as a desert, coral reef or freshwater lake. A habitat can be home to thousands of different species.
invertebrate An animal lacking a backbone. About 90 percent of animal species are invertebrates.
marine Having to do with the ocean world or environment.
nitrogen A colorless, odorless and nonreactive gaseous element that forms about 78 percent of Earth's atmosphere. Its scientific symbol is N. Nitrogen is released in the form of nitrogen oxides as fossil fuels burn.
nutrient A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.
Pacific The largest of the world’s five oceans. It separates Asia and Australia to the west from North and South America to the east.
phosphorus A highly reactive, nonmetallic element occurring naturally in phosphates. Its scientific symbol is P. It is an important part of many chemicals and structures that are found in cells, such as membranes, and DNA.
rainforest Dense forest rich in biodiversity found in tropical areas with consistent heavy rainfall.
reef A ridge of rock, coral or sand. It rises up from the seafloor and may come to just above or just under the water’s surface.
seagrass The name is a misnomer because these are not grasses, but flowering underwater plants. Like land plants, seagrasses use photosynthesis to power the production of food and the release of oxygen. Some 60 different species can be found around the world. How deeply they can grow tends to depend on how clear the water is, and therefore how far down the sunlight can penetrate.
sewage Wastes — primarily urine and feces — that are mixed with water and flushed away from homes through a system of pipes for disposal in the environment (sometimes after being treated in a big water-treatment plant).
species A group of similar organisms capable of producing offspring that can survive and reproduce.
survey (v.) To ask questions that glean data on the opinions, practices (such as dining or sleeping habits), knowledge or skills of a broad range of people. Researchers select the number and types of people questioned in hopes that the answers these individuals give will be representative of others who are their age, belong to the same ethnic group or live in the same region. (n.) The list of questions that will be offered to glean those data.
tidal flat A broad and flat area that usually has a muddy or rocky bottom. It gets its name from the fact that it becomes covered by sea water every time the tide comes in — then drains again when the tide goes out.