Home » Gardening Information » Puzzles
Salient Green—The New Era of Algae
Plants & Gardens News | Volume 22, Number 3 | Fall 2007
by Emily Votruba
An illustration of various diatoms, single-celled algae related to kelp, as depicted by master draftsman and scientist Ernst Haeckel (1834–1919).
While numerous species of flora and fauna are dwindling toward extinction, good old slimy algae are on the rise, clogging waterways and making headlines. In the U.S. alone, harmful algal blooms were reported this summer everywhere from the coastal areas of Maryland, Florida, California, and Texas to rivers in Virginia and New Hampshire and lakes in Minnesota and Vermont. Rampant cyanobacteria closed Wisconsin beaches this past summer; and a genus of green algae called Cladophora that had been mostly eradicated by the end of the 1990s is back, piling up on Lake Michigan's shores and filling the air with a sewagey stink. "Red tides," a term for blooms of harmful algal species that debuted in the 1970s, have been increasing in the Gulf of Mexico and elsewhere since the '80s, destroying coral reefs, thwarting tourism, and threatening commercial fishing. In July 2006, according to the Los Angeles Times, Australia's eastern coast was blighted with the toxic cyanobacterium fireweed (Lyngbya majuscula), which blanketed the ocean waters at a rate of one football field per hour and afflicted unsuspecting fishermen with excruciating skin lesions.
While the new proliferation of algae is cause for concern, we may be able to live in greater harmony with these organisms as scientists discover new uses for algae and develop the technology to revamp a few old ones.
You Can Call Me Algae
Alga is the Latin word for seaweed, but over time algae has become the layman's term for organisms from at least two kingdoms and numerous phyla. In truth, the vast number of organisms called algae have only one thing in common: They all photosynthesize. Otherwise, algae vary greatly in cellular structure, metabolism, and DNA. Members of the algae clan exist in fresh water, saltwater, snow, hot springs, deserts, and even in the pelts of three-toed sloths. Single-celled diatoms and multicellular giant kelp, pond scum, and freshwater seaweed, are all called algae. The fossil record shows that algae have been around in some form or other for more than three billion years—these ancient photosynthesizers are considered the ancestors of land-based plants.
Today, phycologists (algae scientists) use the terms microalgae and macroalgae to distinguish the slime (like fireweed) from the more charismatic, plantlike species, like sushi lovers' nori (a species of Porphyra). Taxonomists are still debating the finer points of the family relationships within this group. Kerry Berringer, a taxonomist and curator of the herbarium at Brooklyn Botanic Garden, spells out the challenge like this: "Red, green, and brown algae are from separate ancient lines—even the chemistry of their photosynthetic pigments is very different. And blue-green algae—cyanobacteria—have much more in common with bacteria than they do with other algae." Green algae—the largest algae group, with about 7,000 species—are the most closely related to higher plants. Genetically speaking, the single-celled green algae called desmids have more in common with the grass on your lawn than they do with the diatoms floating next to them.
Despite their taxonomic differences, members of the algae supergroup have similarities of habit and habitat that have made them successful since the Precambrian era. For one thing, most of them stayed in the water. Aquatic life-forms have reproductive and metabolic advantages over land-based organisms. A lot of that advantage boils down to access. Charles Yarish, a professor of marine biology and seaweed specialist at the University of Connecticut, explains it this way: "Each alga cell has immediate access to the nutrients all around it in the water. The physical burden of gravity requires higher land plants to maintain vascular tissue for support and food transport. But an alga doesn't have this burden." Alga cells don't have to wait in line to eat, and they can put every bit of the energy they gain from photosynthesis to work making more algae, either through growth or reproduction, much of which they do asexually—simply by dividing. Algae are incredibly efficient eating and growing machines, excellent at processing nutrients in the water, converting phosphorus and nitrogen into usable forms, and absorbing minerals and metals like calcium, iron, and potassium. And instead of storing a lot of their energy as starch, which higher green plants use to make support tissue, seaweeds and other algae store a relatively high proportion of it as lipids—which we'll get to in a moment.
Food, Filters, and Fertilizer
Rapid growth and efficient use of nutrients by both macro- and microalgae species can cause humans big problems, but they also make certain algae species very useful to us. Seaweed has long been an excellent source of human food (like laverbread, a Welsh staple made from laver seaweeds Porphyra laciniata and Ulva latissima, and the sea lettuce Ulva lactuca, used in salads by the Scots). Alginates extracted from red and brown seaweed are used as gelling and thickening agents in products as diverse as paint, cosmetics, and ice cream, and as a source for the potassium nitrate in gunpowder.
In other ways, people have been putting algae to work for at least a thousand years. Microalgae's waste-processing prowess was perhaps first discovered by the Aztecs, who were cultivating the cyanobacterium Spirulina before the Spaniards first arrived in Mexico. The Aztecs fed a portion of their sewage to the blue-green algae in Lake Texcoco and then harvested the algae as both a food source and a fertilizer, creating a perfect closed-loop system—an original "green machine." In modern times, bioremediation projects have partially diverted the waters of the Ganges through a series of pools in which microalgae remove organic waste. The cleaned water is siphoned off and diverted for irrigation or further processing. Charles Yarish has spearheaded the development of "integrated multitrophic aquaculture" systems; instead of simply farming or fishing for one species of fish, producers encourage the growth of several interconnected species, such as shellfish, certain seaweeds, and tuna. The seaweed and shellfish serve as a food source and habitat for creatures on which the fish feed, and they also "clean" the surrounding waters. For example, red algae in the genus Porphyra has been shown to reduce waste significantly near salmon cages. Scientists also hold great hope for algae as a means of carbon sequestration: Power plant emissions could be piped into adjacent algal ponds, where—through the natural process of photosynthesis—microalgae would consume carbon and emit oxygen.
Coastal peoples around the world have gathered seaweed for fertilizer for centuries. In Ireland, Wales, and Scotland, red and brown algae are dried and composted for direct use on fields or dried and burned to make potash for chemical fertilizers. The Chinese have been co-cultivating cyanobacteria in their rice paddies for centuries because the blue-green algae make nitrogen available for the rice plants. The largest commercial producer of seaweed fertilizer products today is a Nova Scotia–based company called Acadian Seaplants. It grows and processes a species of seaweed called Norwegian kelp (Ascophyllum nodosum), sold in a liquid form under the brand names Stimplex and Acadian. R.J. Rant, a farmer in Grand Haven, Michigan, has been using Stimplex on his 60 acres of blueberries and in his home garden for the past five years. He sprays the product on plant leaves and also applies it directly to roots, and he says it increases lateral branching and also seems to help plants weather dry periods and fungal infestations.
The Future of Algae
Probably the most exciting potential collaboration between people and algae has emerged in the past 30 years. During the energy crisis in the 1970s, the U.S. Department of Energy began funding studies on the use of algae's stored lipids in biofuel. Much of this work was done at the National Renewable Energy Laboratory (NREL) in Golden, Colorado. Unfortunately, in 1996, funding for algae fuel research was terminated, but scientists working for private companies and at universities are still conducting studies, hoping to develop the technology to make the fuel efficient to produce.
Until recently, the main land-based means of cultivating algae such as the dietary supplement spirulina (Arthrospira species) was the raceway pond—a shallow, ellipse-shaped concrete pool with rotating paddles to circulate the water, continuously exposing all the algae to light and air. According to a conservative estimate by Michael Briggs, a professor at the University of New Hampshire, a system of raceway ponds could produce 5,000 gallons of biofuel per acre per year. Compare that with traditional crops such as soy and corn, which have yields of around 50 to 150 gallons of biodiesel per acre per year. Once harvested, the raceway algae can be cold-pressed to produce a fuel that an NREL study deemed energy-intense enough to serve as jet fuel.
Now scientists are designing "photobioreactors"—self-contained algae greenhouses. By some estimates, the United States could satisfy all its current petroleum needs with 95 million acres of land devoted to algae cultivation—land currently unusable for cultivating other crops. Imagine a future in which every sewage treatment center is also a power plant, constantly producing clean renewable energy. Our waste and energy production could be wrapped up in a great green loop, in which mammoth algal blooms would be a cause for celebration.
Emily Votruba is a freelance writer whose work has appeared in n+1 and Bookforum. She lives in Ithaca, New York.