what's that green stuff?july–august 2010 49 green slimy stuff in the water is benign fish...

46 MinnesotaConservationVolunteer July–August2010 47

Algaeareeverywhere,inoceans,infreshwaterlakesandriv-ers,onland,andevenintheairwebreathe.Sometimescalledpondscumorseaweed, theyareanaturalpartofanyaquaticenvironment.Algaeandfungicanlivetogetherinaformcalledlichensonrocks,walls,andtrees.

Algae occur at the bottom of the food web, making themvital foodsourcesforzooplankton (small invertebratessuchasDaphnia).Inturn,theseinvertebratesareeatenbyfishandotheraquaticanimals.

Similartoalllivingplants,algaeneednutrients—suchasphos-phorus and nitrogen—and light to photosynthesize and thrive.Differentkindsofalgaehavedistinctappearancesandgrowatdif-ferenttimesofyear.Indeed,colorandseasonarehelpfuliniden-tification.Andifyouknowyouralgae,you’llknowwhetherthe

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 sum-

mer. They can form large algal

mats that look like slicks of

spilled paint.

Blue-green algae

This thick algal mat on Little

Rock Lake in Benton County

is bright green, but it’s still

a variety of blue-green algae.

These blooms can smell bad

and produce a foul taste in

drinking water. Blue-green

algae also contain toxins

which cause liver and nervous

system damage if ingested by

humans and dogs.

By Howard Markus and Steve Heiskary

What’s That Green Stuff?

Algae can be vital to a lake’s ecosystem or toxic to wildlife.

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July–August2010 49

greenslimystuffinthewaterisbenignfishfoodoratoxicformthathumansandani-malsshouldavoid.

Algaecomeinmanyshapesandsizes,ranging from microscopic plants (mostalgaefallintothiscategory)tolargeoceankelps,whichcangrowto20feetormore.Theycanconsistofasinglecellorcolonialglobesorlargeribbonsoralmostanyotherplantshapeimaginable.Inwater,algaecanbefree-floatingphytoplanktonorperiphy-ton attached to substrates such as otherplants, rocks, logs, or sediments. Chara, also called muskgrass, is widespread inMinnesotalakes.Ithastheappearanceofasubmergedrootedplantbutisactuallyamulticellulargreenalga.

Seasonal Cycles. In lakesandrivers,dif-ferent forms of algae grow in response tochanges in water temperature, sunlight,andnutrients. In spring, following iceout,diatoms,aunicellularalgae,oftengrowpro-fusely in cool water, which contains silicaand abundant nutrients accumulated dur-ingwinter.Theyusesilicatobuildtheircellwalls.Diatomsgrowquiterapidlyandoftengivethewaterabrownishhue.

Becausetheycannotregulatetheirbuoy-ancyinwater,diatomsrelyonrivercurrentsorwindandwaveactionin lakestokeepthem in the lighted zone, where sunlightpenetratesshallowwater.Intheabsenceofwind,waves,orcurrents,diatomssettletothebottomofthelakeanddie.

Asthewaterwarms,diatomsareoutcom-petedfornutrientsandgivewaytogreenal-gaeoryellow-brownalgae,whichgrowfast-erinthewarmerwater.SomegreenssuchasCladophoramaygrowextensivelyonrocksanddocksinsomelakesandrivers,butmost

greenandyellow-brownformsareuncom-moninMinnesotawaters.

Usuallybyearlysummer,diatoms,greens,andyellow-brownsgivewaytoblue-greenalgae,alsoknownascyanobacteria.Asthelatter name suggests, this type of algae isnot a plant but a photosynthetic bacteria.It grows best with plentiful nutrients andwarm temperatures—common conditionsinmanycentralandsouthernlakes.

Themorenutrientsandlightavailablein a lake, the larger its concentration ofblue-green algae. When algae growth isexcessive,weoftenrefer to itasanalgal bloom. Landowners can minimize theamountofnutrientsthatenterourlakes.Shoreline buffers of natural vegetationandgood lawnpracticeskeep fertilizers,grassclippings,andleavesfromwashingoffyardsandeventuallyintolakes.

Toxic Algal Blooms. Somebloom-formingalgaecontaintoxins,whichcancauseseriousillnessorevendeathinanimalsandhumans.Inmarine(salt)waters, themostcommonbloom-forming toxic algae are dinoflagel-lates.Thesecancause“redtides,”potentiallyresultinginfishdie-offsandmakingseafoodpoisonous to eat. Minnesota lakes occa-sionally have dinoflagellate blooms, whichgivethewaterareddishhue;however,thesefreshwaterformsarenottoxic.

InMinnesotathemostcommonbloom-forming toxic algae are blue-green algae.Though they can bloom any time, blue-greenalgaetypicallyproducebloomsduringmid-tolatesummer,whenpeopleandtheirpetsareenjoyingwarmwatersandsunlight.

Blue-green algal blooms can cause avarietyofproblems, fromfoul tasteandodor in drinking water, to aesthetically

unappealing algal mats, which look likeslicksofbrownorbluishpaintblownbywinds to shore.Most significantly,blue-greenalgaebloomscontainpowerfulnat-uralpoisons.Thesetoxinsincludehepa-totoxinsthatcauseliverinjuryandneuro-toxinsthatactonthenervoussystem.

Contact with water containing thesetoxins has resulted in rashes, respiratoryproblems,andgastroenteritisinhumans.Dogs,livestock,andwildlifearealsohigh-lysusceptibletothetoxins;itisnotunusu-altohearofanimalsgettingsickordyingafterdrinkingorswimminginwaterthatcontainsblue-greenalgae.

Asthecellsinthesebloomsdieoffanddecay,theyconsumeoxygen,oftendras-tically reducing dissolved oxygen levels,whichcanresultinsummerfishkills.

More Algae in Minnesota? Inrecentde-cadesMinnesotahasbeenhavinglongerice-freeseasons,providingmoretimeforalgaetogrowtogreaterdensities.

More algae in lakes could reduce dis-solved oxygen below the thermocline astheydieanddecompose.Thiscouldhavea negative impact on some fish speciessuchaslaketroutandtullibeethatliveinthecoolwatersofdeeplakesandrequirehighoxygenlevels.

Algaewillcontinuetobeanessentialpartofthefoodwebinoceans,rivers,lakes,andallwatersinbetween.Withoutalgae,oceansandinlandwaterswouldnothavefish.Sothenexttimeyouseethat“greenstuff”inthe water, remember that while it mightlookslimy,itisvitaltoaquaticlife.nV

For more information and pictures of blue-green blooms, see http://tinyurl.com/bluegreenblooms.

Top: Periphyton, like these green algae, commonly attach to rocks along the shore of the Mississippi River. Middle: When chunks of filamentous algae detach from a lake’s bottom, they are often blown to shore and can collect near docks. Bottom: Short-lived blooms of reddish algae occur occasionally on Minnesota lakes in spring.

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