More than 20 years ago, unwelcome algae known as “rock snot” began to appear in rivers around the world. Scientists long suspected that this goopy glob was an invader — an alien species that had come from somewhere else. A new study now suggests the algae were there all along — just hiding out.
Researchers now believe the algae are a native species that have simply undergone a recent growth spurt. The burning of fossil fuels is changing Earth’s atmosphere, soils and climate. Those changes appear to be fueling the algae’s highly visible growth.
The species is Didymosphenia geminata (DID-ee-mo-SFEE-nee-ah Jem-in-NAH-tah). But don’t get hung up by its long name. Researchers usually just call it “Didymo.” Since the 1990s, mats of it have rapidly overtaken the bottoms of the world’s streams and rivers. Such a sudden growth is called a bloom. It can harm fish and other aquatic creatures by perturbing their environment. That’s why scientists have been looking for ways to prevent these blooms. One way: They have asked anglers to clean their gear when moving from one river to another. But if the new study is correct — and Didymo has been present all along — scientists may need to rethink how they try to halt the blooms.
When Didymo is not blooming, it’s hard to find, notes ecologist Brad Taylor, of Dartmouth College in Hanover, N.H. These algae are tiny. About as wide as a human hair, they live under the rocks in rivers. Normally, a scientist might scrub six to eight giant rocks to find just one Didymo cell, Taylor says.
When they bloom, however, the algae are hard to miss. In just days, the soda-bottle shaped cells grow white-colored stalks, five to eight centimeters (two to three inches) long. The cells can form mucus-like blobs at the end of those stalks. These blobs merge with other algae cells. The result is what looks like long strands of matted toilet paper. Although they look slimy, the strands feel like wet cotton, Taylor told Science News.
“It’s amazing that a little creature like that can produce three inches of stuff on the stream bottoms [and] that can cover miles of a riverbed,” Taylor says.
The algae blooms can be a big problem. They attract worms that can host a parasite that harms fish. These algae also can trap insects that fish like to eat.
Along with fellow ecologist Max Bothwell, from Environment Canada in Nanaimo, British Columbia, Taylor has been looking for answers to the Didymo problem. They studied patterns in its blooms. They also looked at where the species lives. And they studied fossil records — imprints in old rocks that can help scientists learn about events in the distant past.
All of their research pointed to one simple but surprising conclusion: Didymo is no invader.
“None of it added up that [Didymo] was spreading,” Taylor said. Instead, the researchers hypothesize that the algae had been in the rivers all along. They just lived out of sight when they weren’t blooming. Taylor and Bothwell published their new findings May 7 in BioScience.
Didymo blooms first appeared in the late 1980s in Canada. Within 20 years, similar blooms emerged in the United States, as well as in Europe, Asia and New Zealand. Still later, they hit South America. Researchers assumed they were watching an invasive species spread.
In fact, Didymo have been present on multiple continents for at least 10,000 years, Taylor and Bothwell found.
Previously, Bothwell and other ecologists had showed that Didymo blooms when river levels of an element called phosphorus fall. Didymo needs phosphorus. When the species can’t get enough in its rocky hiding places, it grows long stalks to reach up higher into the water.
That suggests the algal blooms trace to changes in the chemistry of rivers, R. Jan Stevenson told Science News. An ecologist at Michigan State University in East Lansing, he did not work on the new study. He thinks changes in pollution and climate may be driving the Didymo explosion.
Power plants that burn fossil fuels to produce electricity release an element called nitrogen into the air. Eventually, that nitrogen falls to the ground. There it fertilizes the growth of plants. And when their growth takes off, plants will consume other nutrients as well, including phosphorus. Those plants can use up phosphorus that otherwise might have washed from the soil into rivers and streams. Less phosphorus in the water may now give rise to more algal blooms.
“It’s the [hypothesis] that makes the most sense,” Stevenson says.
algae (singular alga) Single-celled organisms, once considered plants, that grow in water and depend on sunlight to make their food.
alien A non-native organism.
bloom (in microbiology) The rapid and largely uncontrolled growth of a species, such as algae in waterways enriched with nutrients.
climate The weather conditions prevailing in an area in general or over a long period.
fossil Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils.
fossil fuels Any fuel (such as coal, oil or natural gas) that has developed in the Earth over millions of years from the decayed remains of bacteria, plant or animals.
hypothesis A proposed explanation for a phenomenon. In science, a hypothesis is an idea that hasn’t yet been rigorously tested. Once a hypothesis has been extensively tested and is generally accepted to be the accurate explanation for an observation, it becomes a scientific theory. Ideas that are based on a hypothesis are referred to as hypothetical.
invasive species (also known as aliens) A species that is found living, and often thriving, in an ecosystem other than the one in which it evolved. Some invasive species were deliberately introduced to an environment, such as a prized flower, tree or shrub. Some entered an environment unintentionally, such as a fungus whose spores traveled between continents on the winds. Still others may have escaped from a controlled environment, such as an aquarium or laboratory, and begun growing in the wild. What all of these so-called invasives have in common is that their populations are becoming established in a new environment, often in the absence of natural factors that would control their spread. Invasive species can be plants, animals or disease-causing pathogens. Many have the potential to cause harm to wildlife, people or to a region’s economy.
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.
parasite An organism that gets benefits from another species, called a host, but doesn’t provide it any benefits. Classic examples of parasites include ticks, fleas and tapeworms.
phosphorus A nonmetallic element that is essential for all life. Its scientific symbol is P.
species A group of similar organisms capable of producing offspring that can survive and reproduce.