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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.
48 MinnesotaConservationVolunteer
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