What's That Green Stuff?

By Howard Markus and Steve Heiskary Blue-green algae A thick, blue-white crust of algae covered this backwater of Dan Lake in Wright County. Blue-green algae can form at any time, but they are most common in mid- to late summer. They can form large algal mats that look like slicks of spilled paint. What’s That Algae canGreen be vital toStuff? a lake’s or toxic to wildlife. ecosystem Blue-green algae Algae are everywhere, in oceans, in freshwater lakes and riv- This thick algal mat on Little ers, on land, and even in the air we breathe. Sometimes called Rock Lake in Benton County pond scum or seaweed, they are a natural part of any aquatic is bright green, but it’s still environment. Algae and fungi can live together in a form called a variety of blue-green algae. lichens on rocks, walls, and trees. Algae occur at the bottom of the food web, making them These blooms can smell bad vital food sources for zooplankton (small invertebrates such as and produce a foul taste in Daphnia). In turn, these invertebrates are eaten by fish and other drinking water. Blue-green aquatic animals. algae also contain toxins Similar to all living plants, algae need nutrients—such as phos- phorus and nitrogen—and light to photosynthesize and thrive. which cause liver and nervous Different kinds of algae have distinct appearances and grow at dif- system damage if ingested by ferent times of year. Indeed, color and season are helpful in iden- humans and dogs. tification. And if you know your algae, you’ll know whether the PHOTO STAFF MPCA BOTTOM: HEISKARY, STEVE BY PHOTO STAFF MPCA TOP: 46 Minnesota Conservation Volunteer July–August 2010 47 wq-s1-90 green slimy stuff in the water is benign fish green and yellow-brown forms are uncom- unappealing algal mats, which look like food or a toxic form that humans and ani- mon in Minnesota waters. slicks of brown or bluish paint blown by mals should avoid. Usually by early summer, diatoms, greens, winds to shore. Most significantly, blue- Algae come in many shapes and sizes, and yellow-browns give way to blue-green green algae blooms contain powerful nat- ranging from microscopic plants (most algae, also known as cyanobacteria. As the ural poisons. These toxins include hepa- algae fall into this category) to large ocean latter name suggests, this type of algae is totoxins that cause liver injury and neuro- kelps, which can grow to 20 feet or more. not a plant but a photosynthetic bacteria. toxins that act on the nervous system. They can consist of a single cell or colonial It grows best with plentiful nutrients and Contact with water containing these globes or large ribbons or almost any other warm temperatures—common conditions toxins has resulted in rashes, respiratory plant shape imaginable. In water, algae can in many central and southern lakes. problems, and gastroenteritis in humans. be free-floating phytoplankton or periphy- The more nutrients and light available Dogs, livestock, and wildlife are also high- ton attached to substrates such as other in a lake, the larger its concentration of ly susceptible to the toxins; it is not unusu- plants, rocks, logs, or sediments. Chara, blue-green algae. When algae growth is al to hear of animals getting sick or dying also called muskgrass, is widespread in excessive, we often refer to it as an algal after drinking or swimming in water that Minnesota lakes. It has the appearance of bloom. Landowners can minimize the contains blue-green algae. a submerged rooted plant but is actually a amount of nutrients that enter our lakes. As the cells in these blooms die off and multicellular green alga. Shoreline buffers of natural vegetation decay, they consume oxygen, often dras- and good lawn practices keep fertilizers, tically reducing dissolved oxygen levels, Seasonal Cycles. In lakes and rivers, dif- grass clippings, and leaves from washing which can result in summer fish kills. ferent forms of algae grow in response to off yards and eventually into lakes. changes in water temperature, sunlight, More Algae in Minnesota? In recent de- and nutrients. In spring, following ice out, Toxic Algal Blooms. Some bloom-forming cades Minnesota has been having longer diatoms, a unicellular algae, often grow pro- algae contain toxins, which can cause serious ice-free seasons, providing more time for fusely in cool water, which contains silica illness or even death in animals and humans. algae to grow to greater densities. and abundant nutrients accumulated dur- In marine (salt) waters, the most common More algae in lakes could reduce dis- ing winter. They use silica to build their cell bloom-forming toxic algae are dinoflagel- solved oxygen below the thermocline as walls. Diatoms grow quite rapidly and often lates. These can cause “red tides,” potentially they die and decompose. This could have give the water a brownish hue. resulting in fish die-offs and making seafood a negative impact on some fish species Because they cannot regulate their buoy- poisonous to eat. Minnesota lakes occa- such as lake trout and tullibee that live in ancy in water, diatoms rely on river currents sionally have dinoflagellate blooms, which the cool waters of deep lakes and require or wind and wave action in lakes to keep give the water a reddish hue; however, these high oxygen levels. MPCA STAFF PHOTOS STAFF MPCA them in the lighted zone, where sunlight freshwater forms are not toxic. Algae will continue to be an essential part penetrates shallow water. In the absence of In Minnesota the most common bloom- of the food web in oceans, rivers, lakes, and Top: Periphyton, like these green algae, commonly attach wind, waves, or currents, diatoms settle to forming toxic algae are blue-green algae. all waters in between. Without algae, oceans to rocks along the shore of the Mississippi River. Middle: the bottom of the lake and die. Though they can bloom any time, blue- and inland waters would not have fish. So When chunks of filamentous algae detach from a lake’s As the water warms, diatoms are outcom- green algae typically produce blooms during the next time you see that “green stuff” in bottom, they are often blown to shore and can collect peted for nutrients and give way to green al- mid- to late summer, when people and their the water, remember that while it might near docks. Bottom: Short-lived blooms of reddish algae gae or yellow-brown algae, which grow fast- pets are enjoying warm waters and sunlight. look slimy, it is vital to aquatic life. nV occur occasionally on Minnesota lakes in spring. er in the warmer water. Some greens such as Blue-green algal blooms can cause a Cladophora may grow extensively on rocks variety of problems, from foul taste and For more information and pictures of blue-green and docks in some lakes and rivers, but most odor in drinking water, to aesthetically blooms, see http://tinyurl.com/bluegreenblooms. 48 Minnesota Conservation Volunteer July–August 2010 49.

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