Migrating Ocean Microbe May Help Protect Coastlines

A single-celled organism may move north with warmer waters and help reduce beach erosion

Pamela Hallock, courtesy of the University of South Florida

From butterflies to lobsters, climate change is expected to spur migration of species, with potentially devastating consequences for ecosystems and economies.

But in the case of a one-celled organism dwelling in the oceans named Amphisteginid foraminifera, a change in its habitat may lessen the devastation to some coastlines at risk from erosion and powerful storms.

In a new study, scientists report that the discus-shaped creatures are likely to shift their ocean range by hundreds of miles as now too-cold ocean regions become more suitable to them.

Because Amphisteginid foraminifera can create sandbar-like structures with their calcareous shells, their migration and number growth in turn could help build additional coastal buffers in areas at risk from rising sea levels, the study says. That could reduce some of the impact expected from the ongoing degradation of coral reefs, it says.

"With their shells, these protozoa produce up to 2 kilograms of calcium carbonate per square meter of ocean floor. This often makes them, after corals, the most important producers of sediment in tropical reef areas," said Martin Langer, a professor at the University of Bonn and lead author of the study in PLOS ONE.

The research builds on existing research examining likely effects to land-based species in a warming world. "In contrast, comparatively few studies have addressed range shifts in marine systems," the study says.

The scientists took water samples from various sites along a stretch of ocean running from Somalia to near Cape Town, South Africa, to determine the range there of the organisms, which are about a quarter of an inch in size.

Expanding into warming water
After comparing the samples with historical data of the species range, they used a computer model to predict what might happen in 2050 and 2100 with warmer temperatures. The organisms need a water temperature of at least 52 degrees Fahrenheit to thrive, a factor that has held back their migration in the past.

The model was able to predict the current range of the protists well, indicating it was a "good model" for the future, said Joan Bernhard, a scientist at Woods Hole Oceanographic Institution who participated in the research.

For 2100, the scientists assumed a water temperature rise of 2.5 degrees Celsius—a number that is "conservative," said Langer. Under that warming scenario, the organisms would move down the coast of Africa about 166 miles—into warmer and warmer waters—through the end of century.

Amphisteginid foraminifera live all around the globe in tropical areas, said Bernhard. They are likely to be offshore in most tropical spots where people like to sit on the beach, she said. They can make "spiderweb" formations in the ocean from their shells, in addition to living on coral reefs, she said.

She said that the migration patterns of the species would likely be similar in areas outside of Africa. If the protists now are held back by cold waters north of Georgia, for example, they eventually might be able to move closer to North and South Carolina as the century progresses, she said.

The study estimates that on a global scale, Amphisteginid foraminifera could spread their range by 112 miles by 2050 and 186 miles by 2100, said Langer. In addition to the migration, their total numbers should grow significantly in a warming world, he said.

May not make up for loss of corals
Richard Norris, a foraminifera expert at Scripps Institution of Oceanography who did not participate in the research, said the study confirms what fossil records reveal from millions of years ago during a warming period.

Then, sandbar structures—produced by a species similar to the studied foraminifera—became more dominant over coral reefs, said Norris. It makes sense that a similar pattern would play out in the future, he said.

"I have no doubt their base conclusion is right," he said of the researchers. "The [amphistegina] will help to offset some of the loss of calcareous sediment from the potential demise of corals." Corals are likely to have more sensitivity than foraminifera to some climate-related challenges such as ocean acidification, because of the different consistency of their shells, according to Langer.

But that doesn't mean, Norris said, that foraminifera are an "ecological savior." While they might help protect coasts by creating offshore buffers, their sandy structures won't make up for the widespread degradation of reefs that could occur with climate change, he said.

Coral reefs consist of complex, three-dimensional frameworks that enhance biodiversity by providing a lot of space for animals to live, explained Norris. A sand flat created by foraminifera is "not going to make up for that."

Additionally, the migrating organisms could become an invasive species in some areas, creating havoc with ecosystems, said Bernhard. "We don't know how that would play out."


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