Freshwater Algae: Identification and Use as Bioindicators - CES (IISc)

40 Pages·2010·1.14 MB·English

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1
Introduction to Freshwater Algae
1.1 General introduction tosynthetic–generatingcomplexcarboncompounds
from carbon dioxide and light energy. Some algae
Algaearewidelypresentinfreshwaterenvironments, have become secondarily heterotrophic, taking up
such as lakes and rivers, where they are typically complexorganicmoleculesbyorganotrophy orhet-
presentasmicro-organisms–visibleonlywiththeaid erotrophy (Tuchman, 1996), but still retaining fun-
ofalightmicroscope.Althoughrelativelyinconspic- damentalgeneticaffinitieswiththeirphotosynthetic
uous,theyhaveamajorimportanceinthefreshwater relatives(Pfandletal.,2009).
environment, both in terms of fundamental ecology The term ‘algae’ (singular alga) is not strictly a
andinrelationtohumanuseofnaturalresources. taxonomic term but is used as an inclusive label for
Thisbookconsidersthediversityofalgaeinfresh- a number of different phyla that fit the broad de-
waterenvironmentsandgivesageneraloverviewof scriptionnotedabove.Theseorganismsincludeboth
the major groups of these organisms (Chapter 1), prokaryotes(Section1.3,cellslackingamembrane-
methods of collection and enumeration (Chapter 2) boundnucleus)andeukaryotes(cellswithanucleus
and keys to algal groups and major genera (Chap- plustypicalmembrane-boundorganelles).
ter 4). Algae are considered as indicators of en- Humanshavelongmadeuseofalgalspecies,both
vironmental conditions (bioindicators) in terms of living and dead. Fossil algal diatomite deposits, for
individual species (Chapter 1) and as communities example, in the form of light but strong rocks, have
(Chapter3). beenusedasbuildingmaterialsandfiltrationmediain
waterpurificationandswimmingpools.Somefossil
algae,suchasBotryococcus,cangiverisetooil-rich
deposits.Certainspeciesofgreenalgaearecultivated
1.1.1 Algae – an overview for the purpose of extracting key biochemicals for
use in medicine and cosmetics. Even blue-green al-
Theword‘algae’originatesfromtheLatinwordfor gae,oftenregardedasnuisanceorganisms,mayhave
seaweed and is now applied to a broad assemblage beneficialuses.ThisisparticularlythecaseforSpir-
of organisms that can be defined both in terms of ulina,whichwasharvestedbytheAztecsofMexico
morphologyandgeneralphysiology.Theyaresimple andisstillusedbythepeoplearoundLakeChadas
organisms, without differentiation into roots, stems a dietary supplement. Spirulina tablets may still be
and leaves – and their sexual organs are not en- obtained in some health food shops. Blue-green al-
closedwithinprotectivecoverings.Intermsofphysi- gaeare,however,arebetterknowninthefreshwater
ology,theyarefundamentallyautotrophic(obtaining environment as nuisance organisms, forming dense
all their materials from inorganic sources) and pho- blooms having adverse effects on human activities
FreshwaterAlgae:IdentificationandUseasBioindicators EdwardG.BellingerandDavidC.Sigee
(cid:1)C 2010JohnWiley&Sons,Ltd
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2 1 INTRODUCTIONTOFRESHWATERALGAE
byproducingtoxins,cloggingwatercoursesandim- unitareawithtime(mgCm−3h−1),andvariesgreatly
pairingrecreationalactivities. fromoneenvironmenttoanother.Thisisseen,forex-
ample,indifferentlakes–whereprimaryproduction
varieswithtrophicstatusandwithdepthinthewater
1.1.2 Algae as primary producers column (Fig. 1.1). Eutrophic lakes, containing high
levelsofavailablenitrogenandphosphorus,havevery
Asfixersofcarbonandgeneratorsofbiomass,algae highlevelsofproductivityinsurfacewaters,decreas-
are one of three major groups of photosynthetic or- ingrapidlywithdepthduetolightabsorptionbyalgal
ganismwithinthefreshwaterenvironment.Theyare biomass. In contrast, mesotrophic and oligotrophic
distinguished from higher plants (macrophytes) in lakes have lower overall productivity – but this ex-
termsofsizeandtaxonomy,andfromphotosynthetic tendsdeepintothewatercolumnduetogreaterlight
bacteriaintermsoftheirbiochemistry.Unlikealgae, penetration.
photosynthetic bacteria are strict anaerobes and do Although algae are fundamentally autotrophic
not evolve oxygen as part of the photosynthetic (photosynthetic), some species have become sec-
process. ondarily heterotrophic – obtaining complex organic
Thelevelofprimaryproductionbyalgaeinfresh- compoundsbyabsorptionovertheiroutersurfaceor
water bodies can be measured as fixed carbon per byactiveingestionofparticulatematerial.Although
Carbon fixed, mg C m−3 h−1
10−2 10−1 1 10 102 103
0
1
2
Very eutrophic
3
Lake George,
4 Eutrophic Uganda
5 Clear Lake
California
Mesotrophic
Oligotrophic Castle Lake,
Lake Tahoe, California
California − Nevada
10 Eutrophic part
Very of Lake Baikal
m oligotrophic
Figure1.1 Algal photosynthesis: h, Lake Vanda,
primary production in six contrast- ept Antarctica
ing lakes. Showing the rate of pho- D 15
tosynthesis (carbon fixation per unit
area) with depth in lakes of vary-
ingnutrientavailability.Theserange
Approximate areal
fUrogmandvae)rytoeueturotrpohpihcic(L(aCkleeaGreLoargkee,, 20 values, mg C m−2 h−1
California; part of Lake Baikal), George 380
30 Clear 116
mesotrophic (Castle Lake, Cali-
Castle 70
fornia), oligotrophic (Lake Tahoe,
Baikal 60
California–Nevada) and very olig- 40
Tahoe 9
otrophic (Lake Vanda, Antarctica). Vanda 0.6
Reproduced, with permission, from 50
HorneandGoldman(1994).
60
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1.1 GENERALINTRODUCTION 3
such organisms often superficially resemble proto- (largely benthic) organisms. Planktonic algae drift
zoa in terms of their lack of chlorophyll, vigorous freely within the main body of water (with some
motilityandactiveingestionoforganicmaterial,they speciesabletoregulatetheirpositionwithinthewater
may still be regarded as algae due to their phyloge- column),whilesubstrate-associatedorganismsareei-
neticaffinities. therfixedinposition(attached)orhavelimitedmove-
ment in relation to their substrate. These substrate-
associated algae are in dynamic equilibrium with
1.1.3 Freshwater environments planktonicorganisms(seeFig.2.1),withthebalance
dependingontwomainfactors–thedepthofwater
Aquaticbiologycanbedividedintotwomajordisci- and the rate of water flow. Build-up of phytoplank-
plines – limnology (water bodies within continental tonpopulationsrequiresalowrateofflow(otherwise
boundaries)andoceanography(dealingwithoceans theyflushoutofthesystem)andadequatelightlevels,
and seas, occurring between continents). This book sotheytendtopredominateatthesurfaceoflakesand
focuses on aquatic algae present within continen- slow moving rivers. Benthic algae require adequate
tal boundaries, where water is typically fresh (non- light (shallow waters) and can tolerate high rates of
saline)andwherewaterbodiesareoftwomaintypes: water flow, so predominate over phytoplankton in
fast flowing rivers and streams. Benthic algae also
(cid:1)
standing (lentic) waters – particularly lakes and requireadequateattachmentsites–whichincludein-
wetlands organicsubstrate,submergedwaterplantsandemer-
gentwaterplantsattheedgeofthewaterbody.The
(cid:1)
running (lotic) waters – including streams and distinction between planktonic and non-planktonic
rivers. algae is ecologically important and is also rele-
vant to algal sampling and enumeration procedures
The distinction between lentic and lotic systems (Chapter2).
is not absolute, since many ‘standing waters’ such
aslakeshaveasmallbutcontinuousflow-throughof
water, and many large rivers have a relatively low
Planktonicalgae
rate of flow at certain times of year. Although the
difference between standing and running waters is
Planktonic algae dominate the main water body of
notabsolute,itisanimportantdistinctioninrelation
standingwaters,occurringasadefinedseasonalsuc-
tothealgaepresent,sincelenticsystemsaretypically
cession of species in temperate lakes. The tempo-
dominatedbyplanktonicalgaeandloticsystemsby
ral sequence depends on lake trophic status (Sec-
benthicorganisms.
tion 3.2.3; Table 3.3) with algae forming dense
Although this volume deals primarily with al-
blooms(seeGlossary)ineutrophiclakesofdiatoms
gaepresentwithin‘conventionalfreshwatersystems’
(Fig. 1.16), colonial blue-green algae (Fig. 1.5) and
suchaslakesandrivers,italsoconsidersalgaepresent
latepopulationsofdinoflagellates(Fig.1.10).During
within more extreme freshwater environments such
the annual cycle, phytoplankton blooms correspond
ashotsprings,algaepresentinsemi-saline(brackish)
to peaks in algal biovolume and chlorophyll-a con-
andsalineconditions(e.g.estuariesandsalinelakes)
centration,andtroughsinturbidity(seeFig.2.8).
and algae present within snow (where the water is
inafrozenstateformostoftheyear).
Benthicalgae
1.1.4 Planktonic and benthic algae
Benthic algae occur at the bottom of the water col-
Within freshwater ecosystems, algae occur either umn in lakes and rivers, and are directly associated
as free-floating (planktonic) or substrate-associated with sediments – including rocks, mud and organic
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4 1 INTRODUCTIONTOFRESHWATERALGAE
Table1.1 SizeRangeofPhytoplankton
LinearSize(Cellor
Category ColonyDiameter,µm) Biovolume*(µm3) UnicellularOrganisms ColonialOrganisms
Picoplankton 0.2–2 4.2×10−3–4.2 Photosyntheticbacteria –
Blue-greenalgae
Synechococcus
Synechocystis
Nanoplankton 2–20 4.2–4.2×103 Blue-greenalgae
Cryptophytes
Cryptomonas
Rhodomonas
Microplankton 20–200 4.2×103–4.2×106 Dinoflagellates Diatoms
Ceratium Asterionella
Peridinium
Macroplankton >200 >4.2×106 – Blue-greenalgae
Anabaena
Microcystis
Biovolumevaluesarebasedonasphere(volume=4/3πr3).
TablereproducedfromSigee,2004.
debris. These attached algae may form major 1.1.5 Size and shape
growths on inorganic surfaces or on organic debris,
wheretheyarefrequentlypresentinmixedbiofilms Sizerange
(withbacteria,fungiandinvertebratesalsopresent).
Underhighlightconditions,thebiofilmmaybecome The microscopic nature of freshwater algae tends
dominated by extensive growths of filamentous al- to give the impression that they all occur within a
gae – forming a periphyton community (Fig. 2.23). broadlysimilarsizerange.Thisisnotthecasewith
Attachedalgaemayalsobefixedtolivingorganisms eitherfreefloatingorattachedalgae.
as epiphytes – including higher plants (Fig. 2.29), In the planktonic environment (Table 1.1), algae
larger attached algae (Fig. 2.28) and large plank- range from small prokaryotic unicells (diameter
tonic colonial algae. Some substrate-associated al- <1µm)tolargeglobularcoloniesofblue-greenalgae
gae are not attached, but are able to move across such as Microcystis (diameter reaching 2000µm) –
substratesurfaces(e.g.pennatediatoms),areloosely just visible to the naked eye. This enormous size
retained with gelatinous biofilms or are held within rangerepresentsfourordersofmagnitudeonalinear
thetangledfilamentousthreadsofmatureperiphyton basis (×12 as volume) and is similar to that seen
biofilms. for higher plants in terrestrial ecosystems such as
Manyalgalspecieshavebothplanktonicandben- tropicalrainforest.
thic stages in their life cycle. In some cases they Planktonic algae are frequently characterized in
develop as actively photosynthetic benthic organ- relation to discrete size bands – picoplankton
isms,whichsubsequentlydetachandbecomeplank- (<2µm), nanoplankton (2–20µm), microplankton
tonic. In other cases the alga spends most of its ac- (20–200µm) and macroplankton (>200µm). Each
tivelyphotosyntheticgrowthphaseintheplanktonic size band is characterized by particular groups of
environment,butoverwintersasadormantmetabol- algae(Table1.1).
ically inactive phase. Light micrographs of the dis- In the benthic environment, the size range of
tinctive overwintering phases of two major bloom- attached algae is even greater – ranging from small
forming algae (Ceratium and Anabaena) are shown unicells(whichcolonizefreshlyexposedsurfaces)to
inFig.2.7. extendedfilamentousalgaeofthematureperiphyton
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1.2 TAXONOMICVARIATION–THEMAJORGROUPSOFALGAE 5
community. Filaments of attached algae such as
Cladophora, for example, can extend several cen-
timetresintothesurroundingaquaticmedium.These
macroscopic algae frequently have small colonial
algaeandunicellsattachedasepiphytes (Fig.2.28),
so there is a wide spectrum of sizes within the
localizedmicroenvironment.
Diversityofshape
The shape of algal cells ranges from simple single
non-motile spheres to complex multicellular struc-
tures(Fig.1.2).Thesimpleststructureisaunicellu-
larnon-motilesphere(Fig.1.2b),whichmaybecome
elaborated by the acquisition of flagella (Fig. 1.2c),
byachangeofbodyshape(Fig.1.2a)orbythedevel-
opmentofelongatespinesandprocesses(Fig.1.2d).
Cells may come together in groups without defined
number or shape (Fig. 1.2e) or may form globular
coloniesthathaveadefinedmorphology(Fig.1.2f,g).
Cells may also join together to form linear colonies
(filaments) which may be unbranched or branched
(Fig.1.2h,i).
Althoughmotilityisnormallyassociatedwiththe
possession of flagella, some algae (e.g. the diatom
Naviculaandtheblue-greenOscillatoria)canmove
without the aid of flagellae by the secretion of sur- Figure1.2 Generalshapesofalgae.Non-motileuni-
face mucilage. In many algae, the presence of sur- cells:(a)Selenastrum;(b)Chlorella.Motileunicell:(c)
facemucilageisalsoimportantinincreasingoverall Chlamydomonas. Non-motile colony: (d) Scenedesmus
cell/colonysizeandinfluencingshape. (e) Asterionella. Motile colony: (f) Pandorina; (g)
Sizeandshape,alongwithothermajorphenotypic Volvox. Unbranched filament (h) Spirogyra. Branched
filament(i)Cladophora. Reproduced,withpermission,
characteristics,areclearlyimportantintheclassifica-
fromBellinger(1992).
tionandidentificationofalgalspecies.Atafunctional
and ecological level, size and shape are also impor-
tantintermsofsoluteandgasexchange,absorption number of constituent species (Table 1.2) for fresh-
of light, rates of growth and cell division, sedimen- waterandterrestrialalgaeintheBritishIsles(taken
tation in the water column, cell/colony motility and fromJohnetal.,2002),withgreenalgaeanddiatoms
grazingbyzooplanktonand(Sigee,2004). far outnumbering other groups – reflecting their
widespread occurrence and ability to live in diverse
habitats. Diatoms in particular (over 1600 species)
1.2 Taxonomic variation – the major
are ecologically successful, both as planktonic and
groups of algae benthic organisms. In addition to the above groups,
Johnetal.(2002)alsolistotherphyla–Raphidophyta
Freshwateralgaecanbegroupedinto10majordivi- (twospecies),Haptophyta(fivespecies),Eustigmato-
sions(phyla)inrelationtomicroscopicalappearance phyta(threespecies),Prasinophyta(13species)and
(Table1.2)andbiochemical/cytologicalcharacteris- Glaucophyta (two species). Although these minor
tics(Table1.3).Someindicationoftheecologicaland phylahavetaxonomicandphylogeneticinterest,they
taxonomic diversity of these groups is given by the havelessimpactinthefreshwaterenvironment.
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s m
TypicalExample SynechocystisMicrocystisChlamydomonasCladophora EuglenaColaciumOphiocytiumVaucheriaCeratiumPeridiniumRhodomonasCryptomonasMallomonasDinobryonStephanodiscusAulacoseiraBatrachospermuBangiaPleurocladiaHeribaudiella
Motility(VegetativeCells/Colonies) BuoyancyregulationSomecanglideSomeunicellsandcolonieswithflagella Mostlywithflagella FlagellatezoosporesandgametesAllwithflagella Mostlywithflagella Somewithflagella GlidingmovementonsubstrateNon-motile Non-motile
ppearance TypicalMorphologyofFreshwaterSpecies Microscopicorvisible–usuallycolonialMicroscopicorvisible–unicellularorfilamentouscolonialMicroscopic–unicellular Microscopic–unicellularorfilamentousMicroscopic–unicellular Microscopic–unicellular Microscopic–unicellularorcolonialMicroscopic–unicellularorfilamentouscoloniesMicroscopicorvisible–unicellularorcolonialVisible–multicellularcushionsandcrustosethalli BritishIsles.
A e
Algae:Microscopical TypicalColour blue-green grass-green Variouscolours yellow-green red-brown variouscolours goldenbrown goldenbrown red brown errestrialalgaewithinth
t
hwater exofaversity 297 992 124 73 54 15 115 652 22 2 aterand
sofFres IndBiodi 1 offreshw
on es4.
Table1.2MajorDivisi AlgalDivision(phylum) 1.Blue-greenalgaeCyanophyta2.GreenalgaeChlorophyta 3.EuglenoidsEuglenophyta4.Yellow-greenalgae:Xanthophyta5.DinoflagellatesDinophyta6.CryptomonadsCryptophyta7.ChrysophytesChrysophyta8.DiatomsBacillariophyta9.RedalgaeRhodophyta10.BrownalgaePhaeophyta DatafromJohnetal.,2002.aBiodiversity:numberofspeciTableadaptedfromSigee,200
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Flagella(VegetativeCells&Gametes) 0 0–many.Similar(isokont)1–2emergent 2unequal(heterokont)2unequal(heterokont)2equal(isokont) 2unequal(heterokont) 1,reproductivecellsonly0 2unequal(heterokont)reproductivecellsonly allo-(alloxanthin),
ChloroplastFine-Structure OuterThylakoidmbranesGroups 00 22–6 33 43 33 42 43 44 20 43 nthin),peri-(peridinin),
Me axa
ol
vi
stics ExternalCovering PeptidoglycanmatricesorwallsCellulosewalls,scalesProteinpellicle PectinorpecticacidwallCellulosetheca(ornaked)Celluloseperiplast Pectin,plusmineralsandsilicaOpalinesilicafrustuleWallswithgalactosepolymermatrixWallswithalginatematrix s,cryptophytes),viola-(
ytologicalCharacteri Starch-likeReserve Cyano-phyceanαstarchαTruestarch βParamylon βChrysolaminarin αTruestarch αTruestarch βChrysolaminarin βChrysolaminarin αFlorideanstarch βLaminarin ndSheath(2003). opresentinchlorophyte
Table1.3MajorDivisionsofFreshwaterAlgae:BiochemicalandC #Pigmentation AlgalDivisionDiag.*(phylum)ChlorophyllsCarotenesCarotenoids β1.Blue-greenalgaeazea-Cyanophytaα,β,γ2.Greenalgaea,bviola-Chlorophytaβ,γ3.Euglenoidsa,bEuglenophytaα,βa,c4.Yellow-greenalgae:,c12Xanthophytaβperi-5.Dinoflagellatesa,c2Dinophytaα,βallo-6.Cryptomonadsa,c2Cryptophytaα,β,ε7.Chrysophytesa,c,c,c123Chrysophyta β,ε,c,cfuco-8.Diatomsa,c123Bacillario-phytaα,β9.RedalgaeRhodophytaa β,ε,c,c10.Brownalgaea,c123Phaeophyta DatafromLee(1997),vandenHoeketal.(1995),Johnetal.(2002)andWehra#Majorpigmentsareshowninboldtype.*Diagnosticcarotenoids,usedforHPLCanalysis(Fig.2.11):zea-(Zeaxanthin:alsfuco-(fucoxanthin,alsopresentinchrysophytes).ααββStarch-likereserves:-1,4glucan;:-1,3glucan.TableadaptedfromSigee,2004.
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8 1 INTRODUCTIONTOFRESHWATERALGAE
In terms of diversity, freshwater algae also have 1.2.1 Microscopical appearance
amajordivisionintoprokaryotes(blue-greenalgae)
andeukaryotes(remaininggroups)basedoncellsize, Thecolouroffreshwateralgaeisanimportantaspect
ultrastructure,antibioticresistanceandgeneralphys- theirclassification(Table1.2),andrangesfromblue-
iology.Evenwithintheeukaryotegroups,fundamen- green (Cyanophyta) to grass green (Chlorophyta),
taldifferencesinphenotypeandmolecularcharacter- goldenbrown(Chrysophyta,Bacillariophyta),brown
istics indicate evolutionary derivation from a range (Phaeophyta) and red (Rhodophyta). Variations in
ofancestraltypes(polyphyleticorigins). colour are shown in Fig. 1.3, and in the colour
C
G
P
Aph
An
M
100µm
Figure1.3 Colour characteristics
ofdifferentalgalgroups.Top:Fresh
lake phytoplankton sample show-
ing colour differences between ma-
jor algal phyla: Dinophyta (brown:
C), Cyanophyta (blue-green: An,
Aph, M) and Chlorophyta (grass-
green: P). Algal genera: An –
Anabaena, Aph – Aphanothece,
C–Ceratium,G–Gomphosphaeria,
M –Microcystis , P –Pandorina.
Bottom left: Synura (cultured alga,
lightlyfixed)showinggoldenbrown
colourofChrysophyta.Bottomright:
EndoffilamentofAulacoseira.gran-
ulata var. angustissima (with ter-
minal spine) from lake phytoplank-
tonshowingolive-greenchloroplasts 20µm 10µm
(Bacillariophyta).
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1.2 TAXONOMICVARIATION–THEMAJORGROUPSOFALGAE 9
photographsofChapter4.Theuseofcolourasatax- tion 2.3.3, Fig 2.11), and have been particularly
onomicmarkercanbedeceptive,however,sincethe useful in the analysis of estuarine eutrophication
normal balance of pigments may vary. Green algae (Section3.5.2).
livingonsnow,forexample,mayhaveapreponder- Visualization of key differences in cell structure
anceofcarotenoidpigments–forminga‘redbloom’ normally requires the higher resolution of oil im-
(HohamandDuval,2001).Heterotrophicalgaetake mersion(lightmicroscopy),transmissionorscanning
upcomplexorganicmoleculesbysurfaceabsorption electron microscopy (TEM or SEM) and includes
(organotrophy)oringestion(phagotrophy),andhave bothinternal(e.g.chloroplastfinestructure)andex-
either retained photosynthetic pigments (photo- ternal (e.g. location/number of flagella, cell surface
organotrophs, mixotrophs) or lost pigmentation ornamentation) features. Comparisons of light and
completely (obligate heterotrophs) (Sigee, 2004). electron microscope images are shown in Fig. 1.4
Even within a ‘normal’ ecological situation, the (light/TEM)andFigs.4.56and4.57(light/SEM).
colour of a particular alga can show considerable
variation(see,forexample,Anabaena,Fig.4.24).
Apart from colour, the other obvious character- 1.2.3 Molecular characterization
istics under the light microscope are overall size,
and identification
whether the organism is unicellular or colonial and
whetheritismotile(activelymoving)ornon-motile.
Although identification of algal taxa is normally
Within different groups, algae may be largely uni-
based on microscopic characteristics (particularly
cellular (euglenoids, dinoflagellates, cryptophytes),
morphology and colour), there are a number of sit-
multicellular (brown algae) or a mixture of the
uations in which molecular techniques have taken
two (other groups). Motility (single cells or entire
precedence,suchasthefollowing.
colonies)isalsoanimportantfeature,withsomeal-
gal groups being entirely flagellate (dinoflagellates, (cid:1)
No clear morphological characteristics are avail-
cryptophytes)whileothersareamixtureofflagellate
able.Thishasparticularlybeenthecaseforunicel-
and non-flagellate organisms (green algae, xantho-
lularblue-greenalgae.
phytes). Other groups of algae are entirely without
flagella, but are able to move by buoyancy regula- (cid:1)
Algae are relatively inaccessible and difficult to
tion(blue-greens),glidingmovementsonsubstratum
visualize.Thisisthecaseforbiofilms,wherealgae
(blue-greens,diatoms)orareentirelynon-motile(red
are enclosed in a gelatinous matrix, and in many
andbrownalgae).
cases are a relatively small component of a very
heterogeneouscommunityoforganisms.
1.2.2 Biochemistry and cell structure (cid:1)
Diversity is being studied within species, where
strainsareoftendistinguishedinbiochemical and
Major biochemical features of freshwater algae in-
geneticterms.
cludepigmentation, foodreservesandexternal cov-
ering (Table 1.3). Different groups have distinc-
tive combinations of chlorophylls and carotenes, Ultimately,speciesdefinitionandidentificationin
while only three groups (blue-greens, cryptomon- bothprokaryoteandeukaryotealgaemaydependon
ads, red algae) have phycobilins. All pigmented al- molecularanalysis,withdeterminationofuniqueand
gaehavechlorophyll-a,whichcanthereforebeused defining DNA sequences followed by development
for the estimation of total biomass (Chapter 2). ofspecies-specificnucleotideprobesfromthese(see
Diagnostic carotenoids have been particularly use- below).Thisapproachwouldbeparticularlyrelevant
ful in high-performance liquid chromatography inthecaseofblue-greenalgae,butthereareanumber
(HPLC)identificationandquantitationofmajoralgal of problems in relation to species-specificity in this
groups within mixed phytoplankton samples (Sec- group(Castenholz,1992):
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10 1 INTRODUCTIONTOFRESHWATERALGAE
Ch
3µm
Figure1.4 Prokaryote features of 1µm
blue-green algae. Top right: phase
contrast (light microscope) image
of live filamentous colony of An-
abaena, showing central patches
of pale chromatin (Ch). Top left: P
transmission electron micrograph of Ca
whole cell of Anabaena show-
Th
ing central patch of granular chro-
matin. Bottom: Detail from top
left, showing fine-structural detail.
Ch – central region of chromatin
Gy
(no limiting membrane), Ca – car- Ch
boxysome (polyhedral body), Gy –
glycogen granule (cyanophycean
starch), Th – peripheral thylakoid
membranes, V – vacuole, P – thin V
peptidoglycancellwall.

(cid:1)
Polyploidy (multiple genomic copies per cell) etal.(2007),forexample,todeterminethetaxonomic
may occur, with variation between the multiple compositionofbiofilms–identifyingbacteria,blue-
genomes. As many as 10 multiple genome copies green algae and some eukaryote unicellular algae.
havebeenobservedinsomeblue-greenalgae. Thetechniqueinvolves:
(cid:1)
Horizontal gene transfer means that some DNA (cid:1)
collecting a sample of biomass from the entire
fragmentsaredispersedoverarangeofspecies.
microbialcommunity
(cid:1)
obtainingaDNAsample;thismayinvolveextrac-
DNA/RNAsequenceanalysis
tion from a mixed environmental sample such as
biofilmorsoil(Zhouetal.,1996)
Analysis of DNA sequences has been widely used
(cid:1)
for the identification of both blue-green (16S rRNA polymerasechainreaction(PCR)amplificationof
genes) and eukaryote algae (18S rRNA and chloro- aspecificnucleotideregion–typically16Sor18S
plastDNA).ThistechniquehasbeenusedbyDroppo rRNAgenes