This type of algae is kelp, and kelp forests are sometimes called the rainforests of the seas. This kelp forest is in Monterey Bay off the coast of California.

Tania Larson, U.S. Geological Survey

Algae may be easy to see, but appearances can be deceiving. There’s an ongoing problem with algae that has pestered scientists ever since they started trying to organize and classify the natural world. Different types of algae may look similar, but they’re actually very different organisms.

Algae may range in color from red to brown to yellow to green. Some types, like phytoplankton, are tiny and visible only under a microscope. Others types, like giant sea kelp, can grow to over 100 feet. Some types of algae are unicellular, which means the entire organism is made of one cell; others are multicellular.

Diatoms are one of the single-celled types of algae. Pictured is a scanning electron micrograph image of Diploneis puella.

USGS Geology and Environmental Change Science Center website

Strangest of all, there are types of algae that sometimes behave like plants — and sometimes behave like animals. Like a plant, these algae use photosynthesis to make food. (During photosynthesis, plants or algae use light from the sun to turn carbon dioxide and water into oxygen and food.) But when sunlight is not available, these organisms can still survive by eating other organisms — including other algae! (What would you call that? Cannibalgae?) That behavior is more like an animal because animals can’t synthesize their own food.

Algae are notoriously difficult to classify. So much so, say some scientists, that maybe the best idea is to stop using the word “algae” altogether — except that it’s been around so long it’s too late to change.

Your cousin Chlamy

In 2007, an international team of biologists looked at all the genes of a simple green alga called Chlamydomonas reinhardtii, or Chlamy for short. Genes carry the instructions of life “written” on tightly coiled molecules called DNA inside every cell. Chlamy’s genetic “instruction book” has about 15,000 genes, which is about 8,000 fewer genes than in humans. When the biologists compared Chlamy’s genes to other organisms, some interesting trends emerged.

A large number of Chlamy’s genes can also be found in flowering plants. But it might be surprising to know that roughly 35 percent of Chlamy’s genes can be found in both flowering plants and humans, the research team reported earlier this year. Plus, about 10 percent of Chlamy’s genes can be found in human cells but not plant cells.

No one is going to invite Chlamy to the family reunion, of course. And Chlamy isn’t that unusual — many different living things have identical genes. But Chlamy is interesting: It shows how evolution can deliver some surprising tricks, like producing algae that is genetically similar to humans and plants.

A red tide is a poisonous bloom of algae that can kill marine life.

NOAA

Scientists have always had trouble classifying algae. In ancient Greece, the philosopher Aristotle — probably the first scientist to try to organize all living things — simply placed algae in with plants. (Plants and animals were “beneath” humans, and humans were “beneath” angels.)

In the 18th century, a Swedish botanist named Carl Linnaeus suggested a system that grouped all plants together and grouped all animals together. Like Aristotle, Linnaeus called algae a plant. Linnaeus’ system also showed how similar animals — such as dogs and wolves, for example — could be grouped together. The system is still in use today, though it has been modified and changed significantly in the past 250 years. But even with hundreds of years of changes, algae stick out like a sore thumb.

“The study of algae has changed a lot, but it has always been a problem,” says Rick McCourt, a biologist at the Academy of Natural Sciences in Philadelphia. McCourt is also a phycologist, or a scientist who studies algae. (Phycology is the study of algae.)

McCourt points out that the algae problem goes back much farther than Linnaeus or even Aristotle. Much farther: The roots of algae’s identity crisis go all the way back to the beginning of life on Earth, billions of years ago.

Bacteria move in

About 3 billion years ago, Earth was a different planet. It was not populated by people, animals or plants, and the atmosphere was mostly carbon dioxide. Earth’s inhabitants were microorganisms such as bacteria, so small they’re impossible to see without the help of a microscope.

So how did that Earth become the planet on which we live? Many scientists who study evolution blame one particular organism called cyanobacteria. (Sometimes known as blue-green algae or blue-green bacteria, these microorganisms were grouped together with algae until just a few years ago.)

When cyanobacteria, or blue-green bacteria (pictured is the cyanobacteria Gloeotrichia stained with sytox green), invaded another organism, algae was the eventual result.

Barry H. Rosen, USGS

“Blue-green bacteria changed the world more than any other group of organisms,” says Brent Mishler, a phycologist at the University of California, Berkeley. Blue-green bacteria were capable of photosynthesis, he says, which means they started taking carbon dioxide and adding oxygen to the atmosphere.

Scientists think that blue-green bacteria are also responsible for algae. Here’s how: These bacteria may have been the first organisms to stay alive through photosynthesis. That means they used sunlight, water and carbon to make their own food.

Other organisms regularly fed on the blue-green bacteria as well. One of these organisms was the ancient ancestor of green algae. But this ancient alga wasn’t green back then — it was colorless.

And one time, when this algal ancestor ate one of these blue-green bacteria, something strange happened. The organism didn’t digest the bacteria — it absorbed it.

Instead of becoming dinner, that bacteria became a permanent resident inside the other organism. Biologists believe that bacteria-inside-an-organism is the oldest ancestor of all green algae. These two organisms each had their own set of genes, but after millions of years and many, many, many generations, the genes mixed and both sets became essential for the alga’s survival. The two organisms had become a single organism.

“It’s the only explanation that makes sense,” says McCourt. “Everything we call green algae descended from a single ancestor, maybe from a single cell, long ago in the ocean or in the freshwater.”

Green algae isn’t the only type of algae. Other types — including brown algae, red algae and diatoms — also evolved in a similar way. “What makes all the algae groups algae is that some of the cyanobacteria went and lived inside them,” Mishler says. “But they were invaded separately.”

Different types of algae may not be related in ancient, ancient history, but every type of algae evolved from an organism that, once upon a time, was invaded by blue-green bacteria. These invaded organisms were not necessarily similar. Green algae and brown algae, for example, are often grouped together because they both use photosynthesis to make food, and because they’re both found in the water. But they have very different family histories. Green algae evolved after one type of organism was invaded by cyanobacteria, and brown algae evolved after a different organism was invaded.

This distinction explains why there are so many different kinds of algae — and why the algae family is still hard to pin down. Scientists have shown that many different types of algae are related only distantly, despite the fact that they may look similar.

And some of these scientists say algae’s classification problem isn’t with algae at all, but with the system we use to organize living things. These scientists advocate for a new system — one based on evolutionary ancestors, rather than on the current appearance and structure of an organism.

Changing classification systems

The original invasion that gave us algae happened billions of years ago, but since then, algae’s evolutionary story has been filled with similar invasions. Even today, it’s easy to see how algae too have invaded other species.

Mishler points out that algae are responsible for the brightly colored plumes that can be observed on giant clams or the vibrant appearance of coral. Algae also live inside octopi. “There’s a parallel story over and over again, with algae invading a host,” says Mishler. “They like to live in other organisms.”

Earlier this year, scientists found an invasion in the making: A sea slug that regularly feasts on algae was found to have absorbed algal genes — the ones used to do photosynthesis.

But just because the invader is the same for all these host organisms doesn’t mean the host organisms are related; it just means they’ve been invaded. And if the evolutionary development of algae is considered, then maybe “algae” shouldn’t be its own group of organisms.

Some biologists, like Mishler, say it’s time to change the system that we use to organize the living world. A better way, they say, would be to organize living things according to how they evolved.

The problem in classifying algae is just one example of the issues that scientists who care about naming things grapple with. And their work is just starting. Dozens of new plant and animal species are found every year, and each one of those new species has to be studied, classified and named.

The system for classifying organisms also gives those organisms their names. It’s important that scientists agree on the same names. “Unless you can name something you really can’t talk about it,” says McCourt. “Giving a species a name is necessary in order to study and understand what it’s doing.”

“If a young scientist wanted to get a good career and go outside and do adventurous things, this would be an exciting career,” says Mishler. “It’s one of the older careers in biology, but it’s still not finished.”

And there will always be new species to find: “There are probably more organisms out there we don’t know than those we do know,” Mishler says.

Going Deeper:

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Chances are, though, you’ve come face-to-face with plenty of these crusty, leafy, or shrubby growths. Lichens live on rocks, branches, houses, even metal street signs. You can find these often colorful organisms almost everywhere—from deserts to rainforests, Antarctica to Africa. They’ve survived trips to outer space, and some scientists suspect there might even be lichens on Mars.

“If you go into your backyard, you will definitely find a lichen somewhere,” says Imke Schmitt, a lichen researcher—called a lichenologist—at the University of Minnesota, Twin Cities.

What you probably don’t realize is that a lichen is more than a single thing. It is a thriving relationship between two different types of living organisms: a fungus and an alga. Neither of these organisms is a plant, so the lichen isn’t a plant either.

Different species of lichens can look very different from each other. Thorsten Lumbsch, a lichenologist at The Field Museum in Chicago, took photographs of two varieties of lichens—a rock lichen (above) and a spot lichen (below)—during a recent

Thorsten Lumbsch

Thorsten Lumbsch

Through photosynthesis, the alga harvests the sun’s energy to make food for the fungus, which provides a place for the alga to live. But the relationship is lopsided, Schmitt says, with algae caged like prisoners—even slaves—inside their fungal hosts.

Around the world, scientists have identified tens of thousands of types of lichens. At least as many probably still await discovery, says Thorsten Lumbsch, a lichenologist at the Field Museum in Chicago.

“Even in North America, there is a huge lack of knowledge” about lichen diversity and biology, Lumbsch says. “There’s a lot still to discover.”

As lichenologists continue to find new species of lichens, they are also working to understand how various species are related to one another. By putting together a lichen family tree, they hope to understand why so many different types of lichens have evolved in so many places around the world.

Most research involves attempts to understand basic facts about the organisms and their interrelationships. But researchers are also teaming up with lichens to monitor the health of the environment, among other applications.

Tough work

Studying lichens is rarely easy. Most species depend on very specific conditions, and scientists can rarely get them to grow in laboratories. This provides lichenologists a great excuse to travel around the world, scouting new specimens and insights.

Lumbsch, for one, makes several trips to Australia and South America each year. In the field, he searches for a group of crusty lichens that tends to be quite tiny—usually less than a few millimeters long. Finding samples takes patience and a trained eye.

“You have to look very closely,” Lumbsch says. “Usually, I know which species I’m interested in and which habitats they grow in. So, I go there and crawl on my knees on the forest floor with a hand lens.”

Like many lichenologists, Lumbsch (far right) travels all over the world to collect specimens. This photograph was taken on a research trip to India in January 2008.

Thorsten Lumbsch

Spotting lichens is challenging enough. Identifying them is even harder. Many species look exactly alike, even when they are only distant cousins. Closely related species, meanwhile, can live in totally different environments, or on opposite ends of the Earth. (One species, for example, is found only near both poles.)

When they’re done collecting samples, lichenologists bring their catch back to the lab. Under a microscope, the researchers classify samples by structure and color. Then, they grind specimens into a powder, from which they extract genetic material. These DNA molecules, which appear in all cells, make up genes, which determine how organisms look and work.

The more closely related two organisms are, the more similar their DNA will be. Comparing DNA from different species, then, can give scientists an idea of when each group split off from a common ancestor. Researchers use this information to build lichen family trees that depict kinship between species.

“Once we have these trees, we can ask a lot of interesting questions,” Schmitt says.

For example, family trees can help explain what the first lichens looked like, how they have evolved over time, and how far any given species has moved around the globe. Such insights should provide a window into our planet’s distant past. Some researchers think that lichens were the first organisms to live on land, long before plants evolved to do so.

“[Lichens] have an extremely long history,” Schmitt says. “This is what we are trying to uncover by building family trees.”

The work is slow going, she adds. “But we are beginning to see a picture emerging.”

Environmental police

Despite their reputation as scientific curiosities, lichens have a practical side. Throughout history, people have used different species to make dyes for fabrics, poisons for arrowheads, and “green”-smelling scents for perfumes. Birds use lichens to make nests. Reindeer and other animals, including some people, eat them. (Don’t try this at home—some species taste awful!)

In modern times, scientists have found a new role for these growths: as environmental watchdogs.

Although lichens can live in some of the harshest environments on Earth, Schmitt notes that they “are very sensitive to any kind of change that humans put on the environment.”

Some species of lichen are highly sensitive to changes in the environment.

Tsnena/Wikipedia

Studies show that some species quickly disappear when exposed to air pollution. These sensitive types also suffer from habitat loss due to logging, construction, or other environmental disturbances. The presence of lichens in an ecosystem, then, generally signals that the air is clear and the environment healthy. Their disappearance, on the other hand, can be a warning sign.

Lichens are good monitors of air quality. In fact, studies have shown higher rates of lung cancer in people who live in areas where sensitive lichens have died off. As a result, Lumbsch says, some European cities require developers to confirm the presence of sensitive lichens as a sign of habitable air quality before building new homes. Where lichens reside, city planners can feel confident that homeowners will have good air to breathe.

Among other projects, Lumbsch and his colleagues are looking at the effects of climate changes on lichen populations. Some day, he says, lichens might add service as global-warming sentinels to their list of accomplishments.

Lichens have long been overlooked. Chat with a lichenologist, though, and you’ll find plenty about these underappreciated growths to like, if not love!

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Scientists have known that scattered bits of kelp grow in the warm tropics in places where cold water wells up from below. Now, an international team of researchers has used worldwide ocean studies to predict and find tropical locations where whole forests of kelp grow.

Thick forests of kelp support lots of marine creatures and lure visitors like this Galápagos iguana.

S. Connell

The team recently found kelp forests in deep waters off the Galápagos Islands, about 600 miles west of Ecuador in the Pacific Ocean.

What’s more, a new computer model predicts that there may be many more of these rich ecosystems in tropical waters around the globe. The model has identified 23,500 square kilometers (9,075 square miles) of tropical ocean hideouts where kelp might be growing.

Kelp lives in chilly places because there’s extra nitrogen available in cold water that seeps up from ocean’s bottom. Nitrogen is an essential nutrient for the algae. Kelp also needs sunlight to grow.

Michael Graham of Moss Landing (Calif.) Marine Laboratories and colleagues used recently compiled data about the oceans to look for spots that might meet these conditions. Their model predicted that kelp would grow in all the tropical spots where it had previously been collected.

But the team’s model also predicted that kelp would be found in an area of the Philippines that almost nobody knew about. The area was mentioned in an old paper—written in Russian—that reported a few kelp specimens in that part of the Philippines. One scientist involved in the new study knew about that spot, but he kept the knowledge secret until after the model had predicted it.

In the Galápagos, Graham and colleagues also explored places where the model had predicted kelp forests might grow. The expedition had a rocky start.

The first robotic, remotely operated vehicle (ROV) that went underwater came off the line that connected it to the surface. The second ROV, which went down to look for the first one, had an electrical malfunction and lost its ability to “see”.

So, the scientists had to explore by scuba diving instead. During their first dive, they hit the jackpot. Graham reports that, “I went down, cleared my mask, and there was kelp right in front of me.”

They found abundant kelp in eight places around the Galápagos.

Along with other work, researchers say, the new study points out how much they still have to learn about ecosystems that live in the ocean’s depths.—Emily Sohn

Going Deeper:

Milius, Susan. 2007. Jungle down there: What’s a kelp forest doing in the tropics? Science News 172(Sept. 29):196. Available at http://www.sciencenews.org/articles/20070929/fob3.asp .

Sohn, Emily. 2006. Coral gardens. Science News for Kids (March 1). Available at http://www.sciencenewsforkids.org/articles/20060301/Feature1.asp .

______. 2005. Fishing for giant squid. Science News for Kids (Nov. 2). Available at http://www.sciencenewsforkids.org/articles/20051102/Feature1.asp .

______. 2004. Explorer of the extreme deep. Science News for Kids (Nov. 10). Available at http://www.sciencenewsforkids.org/articles/20041110/Feature1.asp .

In remote Arctic lakes, the population changes among certain species of microscopic algae chronicle variations in climate over the past 150 years.

John P. Smol

A recent study focused on changes at high altitudes way up north from Canada to Russia. Many of the lakes were on islands in the Arctic Ocean. They were too far away from civilization for people’s activities to directly influence them.

These lakes freeze over in the winter. That makes the plants and animals that live in them very sensitive to changes in climate. If temperatures warm up even just a few degrees, algae have a longer growing season and so do the animals that eat the plant material.

To learn more about how aquatic life has changed over the years in these remote places, scientists from Queen’s University in Kingston, Ontario, took 55 samples of sediment from the bottoms of dozens of lakes.

Within the samples, they counted remains of tiny creatures including water fleas, insect larvae, and algae called diatoms. The team recorded the numbers of these lake inhabitants at different depths. The deeper the sediment, the older it is.

Counting the remains of tiny creatures, such as this diatom, can reveal what the climate was like years ago.

Kathleen Rühland

Results showed that ecosystems started to change in many of the lakes about 150 years ago. Populations of water fleas and algae-eating insect larvae increased, for example. And one type of diatom replaced another.

The researchers speculate that the shift was a result of climate change. Warming kept lakes unfrozen for a longer period each year, they say. Some species thrive in those conditions. Others do worse.

The new study didn’t look at what is causing global warming in the first place. Instead, it illustrates that minor shifts in temperature can have major effects on life around the globe.—E. Sohn

Going Deeper:

Perkins, Sid. 2005. Warm spell: Arctic algae record shift in climate. Science News 167(March 5):148. Available at http://www.sciencenews.org/articles/20050305/fob3.asp .