第六講第二節(jié)

大型底棲海藻生態(tài)主要內(nèi)容Whatareseaweeds?底棲藻類固著生長(zhǎng)對(duì)光的需求產(chǎn)生形態(tài)上的適應(yīng)Seaweed的種類：綠藻、褐藻、紅藻Grazers,competitionanddefenceSeaweedaspartofanecosystemTherigoursofseaweedlifeWhereverseaweedsgrowtheyhavetocompeteforspace,inorganicnutrientsandlight.Theyarealsoinconstantdangerofbeinggrazedonbygastropods（腹足動(dòng)物）,fish,seaslugs（海蛤蝓）andseaurchins（海膽）andhavesomesinistertacticsforputtingoffpredators.An“army”ofLittorinasnailsgrazinggreenseaweedsformarocksurface(Fig.p59)Fightingforspace1)種內(nèi)競(jìng)爭(zhēng)：whenthereismasssettlingandgerminationofsporesofthesamespeciesinaconfinedarea,competitionnaturallyoccursbetweenthethalli(葉狀體).Ingeneralthisresultsinaninverserelationshipbetweendensityandsize.Thisisparticularlyapplicabletostandsoffast-growing,short-livedspeciessuchasUlva(石莼),Bangia（紅毛菜）,Enteromorpha（滸苔）andPorphyra（紫菜）.Thosemuchslowergrowingencrustingcorallinespeciescompeteforspace:theyendupgrowingintoandovereachother,sometimesbecomingquiteindistinct（模糊的）asindividuals.2）種間競(jìng)爭(zhēng)：并不一定是大的藻類在空間競(jìng)爭(zhēng)中就獲得優(yōu)勢(shì)，例如大型褐藻Egregia

laevigata（優(yōu)秀藻）就競(jìng)爭(zhēng)不過(guò)較為小型的紅藻，因?yàn)檫@些小型的藻類能夠快速地占領(lǐng)空間，使得大型褐藻的孢子難以附著并萌發(fā)。3）與動(dòng)物的空間競(jìng)爭(zhēng)：

barnacles（藤壺）、mussels（貽貝）等也是大型藻類空間的競(jìng)爭(zhēng)對(duì)手。

Therearemechanismsbywhichseaweedinadvertently(不經(jīng)意地)helpstostripthecreaturesfromtherocks,socreatingaspaceinwhichtogrow.TherobustPostelsia(囊溝藻)inhabitspartsoftheshorethatarealsooccupiedbybarnaclesandmussels.SmallPostelsiahavebeenseengrowingfirmlyattachedtobarnacles.Whentheyreachacertainsize,theincreaseddragcausestheseaweed,togetherwiththeattachedbarnacle,toberippedfromtherocksurface.ThebareareaofrockisimmediatelycolonisedbyPostelsiaspores.4)附生植物epiphytesOneofthemosteffectivewaystogaininganadvantageinthequestforspaceandlightistogrowonthesurfaceofamovinganimaloronthesurfaceofanotherseaweed.Mostseaweeds,fromencrustingcorallines(鈣質(zhì)的)tolargemembranousspecies,cangrowasepiphytes,butveryfewseaweedshavetolivethisway.Fig.p65Mostepiphyticspeciesarefastgrowing,short-livedandfilamentous,forexample,絲狀的紅藻Polysiphonia

lanosa（多管藻）經(jīng)常附生于Ascophyllum（囊葉藻）的葉狀體上。

Generally,epiphytesdonotgrowonrapidlygrowingpartsofthethallus.ThereforeLaminaria(海帶)andMacrocystis(巨藻)stipes(葉柄)mayhavelargestandingcropofepiphyteswhereastherapidlygrowingfronds(葉面)orbladesarelargelyfreeofepiphytes.Fast-growingspeciessuchasUlvaandPorphyraarerarelycoveredwithepiphytes—theysimplygrowtoofastfortheepiphytestotakehold.5)防止被附生植物附著

Epiphytescanharmtheirhostsbyblockingoutthelightandtakingupnutrientsfromthesurroundingwater.Layerofepiphytescanactaseffectivebarrierstoexchangeprocesses,includinggaseousexchange,reducingthehost’sgrowthrate.Somespecies,includingChondrus

crispus(皺波角叉菜),Halidrys

siliquosa（角長(zhǎng)角藻）,regularlyslough（脫落）theirsurfaces,therebyriddingthemselvesofanybuildupofepiphytes.Enteromopha

intenstinalis（腸滸苔）constantlyproducesnewcellwalllayers,whilesheddingouterlayersofthewall,toensurethatitremainsepiphytefree.Somespeciesproducechemicaldeterrentstopreventepiphytessettling.Phenolics(苯酚)andhalogenatedlipids（鹵化油脂）arethoughttoplaysucharole.Tryingnottobeeaten:Adaptationsinbenthicalgaeagainstgrazing1）藻體形態(tài)AlgalmorphologyManygrazersshowconsiderablespeciesselectivityandthismayberelatedtoalgalmorphologyorsize.Grazingdifficultyincreasesfrommicroalgae(diatoms,blue-greenalgae)throughfilamentous（絲狀體，如剛毛藻、水云）,foliose（葉狀體，如石莼）,corticated（帶外皮的，如軟骨藻）,leatheryform（革狀種類，如海帶、墨角藻）,cartilaginousform（軟骨質(zhì)形態(tài)，如仙掌藻、珊瑚藻）andultimatelytocrustosecorallinealgae（殼狀、珊瑚狀藻類，如石枝藻）.Somealgaeareabletogrowfastenoughtoescapegrazingbybecomingtoolargeforgrazerstodealwiththem.對(duì)于某些具有不同類型生活史的藻類來(lái)說(shuō)，可以通過(guò)藻體不同階段的形態(tài)變化來(lái)減輕動(dòng)物的捕食壓力，如Scytosiphon

lomentaria(萱藻)，其葉狀體階段生長(zhǎng)很快，抵御蝸牛（Littorina

littorea

）捕食的能力很低，其殼狀體很少被蝸牛所取食；在蝸?；顒?dòng)最活躍的夏季，盡管環(huán)境條件很適合葉狀體生長(zhǎng)，但是萱藻還是以殼狀體形式存在，以降低動(dòng)物捕食壓力。Littorina

littorea

喜歡吃皺波角叉藻（Chondrus

crispus）的孢苗，但是對(duì)成體卻不感興趣。南太平洋島嶼中的某些馬尾藻與喇叭藻等的葉狀體變得很粗糙以及多刺，可以有效地抵御動(dòng)物的捕食,如圖喇叭藻Turbinaria；2）特殊的棲息地SpecialhabitatRock-boringalgaewhichoftenaboundoncoralreefs,althoughsufferfrompoorlight,areprotectedfrommostgrazersduetotheirspecialhabitat.3)藻體表面鈣化

Calcificationofsurface在熱帶海域，植物群落缺少大型種類，許多種類以鈣化的形態(tài)存在，例如珊瑚藻科植物，其鈣化形態(tài)對(duì)在高捕食壓力下具有重要的存活意義。如鈣質(zhì)紅藻Peyssonnelia

squamaria(耳殼藻）（左），鈣質(zhì)綠藻Halimeda

copiosa（仙掌藻）（右上），鈣質(zhì)褐藻Padina

boergesenii（團(tuán)扇藻）（右下）4）釋放有毒化學(xué)物質(zhì)Releaseoftoxicchemicalcompounds綠藻、褐藻、紅藻中的某些種類能釋放諸如萜類化合物、多酚、生物堿等化合物，這些化合物的存在能有效地抵制動(dòng)物的捕食；一般來(lái)說(shuō)，能釋放有毒物質(zhì)的種類大多局限于熱帶海域，因?yàn)樵跓釒ШＳ蛑袆?dòng)物的捕食壓力（尤其是魚類的捕食壓力）很大，使得底棲藻類產(chǎn)生進(jìn)化上的相應(yīng)機(jī)制；例如，Laurencia

obtusa(凹頂藻)能通過(guò)產(chǎn)生溴化物來(lái)逃避很多草食動(dòng)物的捕食，如海膽等，溴化物對(duì)海膽的卵具有很強(qiáng)的毒性；某些藻類的藻體中含有相當(dāng)高分量的丹寧酸，使得它們散發(fā)出異常的氣味，口感差，使其它動(dòng)物不喜歡吃；褐藻經(jīng)常能產(chǎn)生一些酚類化合物，他們是一些抗菌化合物，也能使無(wú)脊椎動(dòng)物不去吃它們；網(wǎng)地藻中的一些熱帶種類能產(chǎn)生大量萜類化合物，如在網(wǎng)地藻Dictyota中萜類化合物的含量能達(dá)到藻體干重的5％；褐藻中的海帶、綠藻中的羽藻、紅藻中的海門冬和柏桉藻，能累積大量的碘，碘的釋放過(guò)程能阻止動(dòng)物的捕食；某些藻類分泌的有毒化合物能通過(guò)食物鏈傳遞給人類，例如，從齒形蕨藻（Caulerpa

serrulata）的藻體中已經(jīng)分離出蕨藻紅素和蕨藻毒素兩類化合物，它們能對(duì)小鼠造成毒害作用，在熱帶海域密集的海藻床上，這些毒素通過(guò)無(wú)脊椎動(dòng)物、魚類，進(jìn)而傳遞給人類，對(duì)人的健康造成影響；一些有毒的珊瑚魚類，其毒性是通過(guò)攝食某些有毒藻類而獲得的，如從易氏鞘絲藻和巨大鞘絲藻中獲得的毒素，能對(duì)人體造成皮膚病；酸藻藻體的液泡中含有硫酸，其濃度足以將海膽的牙齒腐蝕掉。HerbivoresarenotallbadThoughseaweedsarefoodforawholehostofherbivores,ingenerallessthan10%ofbiomasstendstobeactivelygrazed.Manyofthemolluscs（軟體動(dòng)物）

thatappeartobegrazingontheseaweedsareactuallyeatingthefilms（膜）ofepiphytic（附生植物的）microalgaeandbacteriathatgrowonthesurfacesoftheseaweed.適當(dāng)?shù)牟妒硥毫δ芴岣咴孱惖亩鄻有?，例如海膽?duì)海藻床造成破壞，主要是通過(guò)破壞大型藻的固著器等，使藻體從固著物上脫落漂走，這樣就那些因大型藻類的遮蔭作用而生長(zhǎng)不良的種類長(zhǎng)起來(lái)，提高生物多樣性?！癏ousebuilding”amphipods(片腳類動(dòng)物)and“farming”fishSomesurprisingassociationshavedevelopedbetweenseaweedsandgrazinganimals.Somespeciesofseaslug(海蛤蝓),forexample,grazespecificallyonseaweedsthatcontainagentsfordeterring(阻止)fish.Bystoringtheanti-grazingagentinitsowntissuestheseaslugthenhasadeterrenttostopitselfbeingpredateduponbyfish.ACaribbeanamphipodconstructsenclosuresfromDictyota(網(wǎng)地藻)thalli,encouragedbychemicalsreleasedbytheDictyotaitself.Thechemicalsarereleasedtodeterfishgrazing,andtheenclosuresthereforealsoprotecttheamphipodsformpredatoryfish.Thereareevenexamplesof“farmingfish”(speciesoftropicaldamselfish(小熱帶魚))thatmaintainspecificstandsofseaweedbycarefulselectivegrazing.Sometimestheymaintain“pastures”(牧場(chǎng))ofjustonspeciesoralimitednumberofspeciesoverlargeexpansesofreefs.TheeffectofgrazingandcompetitiononzonationItisacommonlyheldviewthattheupperlimitsofaparticularspeciesontheshorearesetbythetolerancestooneormoreofthephysicalstresses,suchasdesiccation(干燥),salinity,temperature,light,etc，whilethelowerlimitsaresetbytheeffectofgrazingandcompetition.Inthesubtidalzonelightistheobvioussinglemoredominantfactorindeterminingthedistributionofseaweedsandzonationpatterns.Theintertidalregionissomewhatmorecomplicatedsincenoneofthephysical“stressfactors”actinisolation.Ratherthanbeingaresponsetooneparticularstress,distributionlimitsresultfromtheinteractionofseveralfactorsprevailing(占優(yōu)勢(shì)的)ataparticularplaceonashore.Amoreaccurateinterpretationofthecausesofzonationisprobablythatthe“potential”limitsofthedistributionsofaspeciesaresetbyphysicalandchemicallimitations.Theactualdistributiononashoreisfinelytuned(調(diào)節(jié))bybiologicalinteractionssuchasgrazingpressureandcompetition.SeaweedaspartofanecosystemThetotalweight,orbiomass,ofseaweedonashorecanbeimpressive,especiallywhensubtidalkelpforestsareconsidered.Theproductivityofseaweedcommunitiesisequalto,orinmanycasesgreaterthan,thatofterrestrialplant-basedsystems.

Laminaria-dominatedcommunities:2kgcarbonperm2

Postelsia(囊溝藻)communities:uptoamassive14kgcarbonperm2intensivealfalfa(紫花苜蓿)crops：

1-2kgcarbonperm2Temperatetreeplantationorgrassland:lessthan1kgcarbonperm21)食物來(lái)源SeaweedasafoodsourceSeaweedsarepartofacomplexecosysteminvolvingmanydifferenttypesofanimals.Manyofthefiner(好的)seaweedsarevaluablefoodsources,yetthelargerspeciesarenotgrazedontoagreatextent.Inthecaseoflaminaria(海帶),forexample,onlyabout1%ofthethallusisdirectlyeatenbyherbivoressuchasgastropods（腹足動(dòng)物）,seaurchins（海膽）andfish.Bitsandpiecesconstantlybreakofffromthemainthallusandprovidefoodfordebrisfeederssuchascrabs,seacucumbers(海參)andamphipods(片腳類動(dòng)物).Thesmallerfragmentsarerichsuppliesforfilter-feedingorganismssuchasmussels（貽貝）,barnacles（藤壺）,tunicates（被囊類）,anemones（?？゛ndpolychaeteworms(多毛類).Detachedseaweedswashedupontheshoreareanothervaluedresource.2)分泌粘液MucusproducersSeaweedsreleasesugarsandaminoacidsintothewaterasaresultofdamageorduetoregulationoftheirmetabolisminresponsetoenvironmentalstress.Thesesubstancesarereferredtoasdissolvedorganicmatter(DOM)anditisthoughtthatupto30%ofthecarbonassimilatedbyLaminariamaybereleasedintheformofDOM.Theseaweedsplayaroleintheregulationofbacterialactivitywithincoastalwaters.AsthebacteriabreakdowntheDOM,nutrientssuchasnitrogenandphosphorusarereleasedbackintothewaterandcanbetakenupagainbytheseaweedfornewgrowth.3)seaweedasshelterTheseassemblagesofseaweedsandanimalsattractfishfortherichpickingstheprovide.Butitisn’tjustthefoodthatattractsthefishsincethedensegrowthofseaweedformaneffectiverefugefromlargerpredatorssuchasbirdsanddolphins.Shoals(魚群)ofplankton-eatingfishhideamongststandsofseaweed,comingoutofcovertofeedonlyatcertaintimesoftheday.Somefishhaveanelaboratecamouflage（偽裝）,suchasthesargassumfish(Histrio

histrio)七、Seaweedlife

大型海藻生活的環(huán)境Theregionbetweentheoceanandthelandisademandingplaceinwhichtolive.Itisaplaceofextremesdominatedbytidesandwaves.Seaweedshavetobeabletocopewiththeriseandfallofthetides.1、Tidalpatterns潮汐規(guī)律Therearethreemainclassesoftidalcycles:1)Diurnaltide全日潮

withonehighandonelowwaterperday.forexample,partsoftheGulfofMexico2)Semiduirnaltide

半日潮

withtwohighandtwolowtidesinadayforexample,Atlanticcoastline3)Mixedtide混合潮、不規(guī)則半日潮

occurtwiceadaybutthehighsandthelowsareofunequalamplitudes.forexample,PacificadIndianOceancoastsWhatcausesthetides?Tidesareproducedbythegravitational（萬(wàn)有引力）effectsofthemoonandtoalesserextentthesun.Springtides

大潮themoonandsunareinlinewiththeearth,whichoccurstwiceamonthNeaptides

小潮themoonandsunareatrightanglesandhave,onaverage,20%loweramplitudesthanspringtides.SeaweedsandtidesAnyseaweedthatgrowsontheshorebetweenthelowestandthehighesttidelevelswillbeexposedtotheairatsomepoint,maybeonceortwiceaday.2、ZoneoftheshoreCertainspeciesarespecifictoparticularregionsorzones.Thezonesaredelineatedbycriticaltidelevelsthatgovernhowlongtheregionissubmergedorexposed.Whetheraspeciescangrowinaparticularzonedependsonitstolerancetodesiccation,temperaturestress,saltstressandwaveaction.ThreezonesoftheshoreIntertidalorlittoralzone

潮間帶

Theshorethatliesbetweentheextremehighwaterofspringtidesandtheextremelowwaterofspringtides.Supralittoralzone

潮上帶

Theregionabovethelittoralzonethatreceivesspray.Subtidalorsublittoralzone

潮下帶

Thepermanentlysubmergedregionthatliesbeyondtheextremelowwatermark.TheintertidalzoneWorldwidestudieshaveidentifiedthreeregionswiththeintertidalzone.1)thereisanuppermoststripofdesiccation-tolerantlichens(苔蘚、地衣)orcyanobacteriathatoftenhaveobviouspopulationsoflittorinidsnail(濱螺).2)thenextzonedowntheshorecomprisesawidediversityofseaweedstogetherwithbarnacles(藤壺)andlimpets(帽貝).3)thelowermostpartoftheintertidalzoneharboursadiversecommunityofseaweedspeciesincludingredencrustingandcorallinealgae.ThesubtertidalzoneThekelpsoftemperateandsometropicalshoresgrowwithinthiszone.Thelowermostregionofthiszoneisneverexposedtotheairandisdominatedbyavarietyoflargecanopy-formingseaweedswithdiverseunderstoreycommunitiesofpredominantlyredandbrownspecies.Stillfurtherdown,wherelighthardlypenetrates,ishometoencrustingredalgae.3、theproblemsofdesiccation（干燥）Seaweedlivingintheintertidalzonemayfacelongperiodsoutofwater,buttherearevariousstrategiesforkeepingwaterlosstoaminimum.Evenwhenseaweedsdodryouttheyhavearemarkableabilitytorecoveroncethetidereturns.SafetyinnumbersUnderstoreylayerTheconsequenceofthissortoflayeredstructureisthatitisonlythosefrondslyingonthesurfacethatwillbeexposedtotheharshcondition.Tufts(一簇)offilamentsWhenthetidegoesoutthetuftsactuallyretainalotofwaterbetweenthefilamentssothatevenaftertheyhavebeenexposedtotheairforaconsiderabletimetheinteriorofthetuftremainsmoist.PreventingwaterlossDesiccationcanbeextremesuchthatintertidalseaweedscanloseupto90%oftheirtissue.\waterwhenexposedtotheair,especiallyifthereisabreeze(風(fēng))andhumidityislow.Thespeedwithwhichthishappensdependslargelyonthesurfaceareatovolumeratioofathallus,thelargerthisratio,thefasterthewaterlosses.Smallseaweed,branchedseaweed.Someseaweedcouldwithstandacertainamountofdesiccationduetothepresentofpolysaccharideswithintheirinnercortex(皮質(zhì))ormedulla(髓)thatbindwithwater.Otherseaweedsexudemucusthathelpstoslowdowntherateofevaporation.潮間帶藻類光合作用的變化Themostobviousfactorthatdeterminedwhetherornotaspeciescansurvivelongperiodsoutofthewateriswhetheritisabletophotosynthesisintheair.Aslongastheseaweedsdonotdryout,manyspeciesphotosynthesisinairatratessimilartothosemeasuredwhentheyarefullysubmerged.However,astheybegintodryouttheirabilitytophotosynthesisdiminishes.Forexample,photosynthesiseifLaminara,evenwhenmildlydesiccated,isgreatlyreducedwhereasUlva

continuesphotosynthesisdownto35%waterloss.SomespeciesofFucusphotosynthesisewhendesiccateddowntotissuewatercontentsoflessthan30%.Seaweedsrecovertheirfullphotosyntheticrateswithinhours.ArareexampleofPelvetiacanaliculata(溝鹿角菜)inwhichperiodsoutofwaterareabsolutelyessential.Ifitissubmergedformorethan6hr,itactuallystartstodecay.4、DealingwithsaltstressInmostoceansaroundtheworldthereareabout35gramsofsaltineverylitreofwater.Therearenotableexceptionstothis,suchastheBalticSea,whichhasmuchreducedsalinitiesofbetweenthreeand10duetotislargeinfluxoffreshwater,whiletheArabianGulf,MediterranceanandRedSeahavesalinitiesupto45ormoreduetohighratesofevaporationandtheirsemi-enclosednature.Whenseaweedsareexposedtorainatlowtide,theyexperienceadramaticreductioninsaltconcentration.Incontrast,whenwaterevaporatesfromthesurfacesofseaweeds,saltsintheremainingwaterbecomegreatlyconcentrated,Bothloweredandeleatedchangescauseaseverestrainonthecellsoftheseaweeds,requiringswiftmetabolicactiontopreventpermanentdamage.Insomeregions,suchasMoroccan(摩洛哥)estuary,theevaporationofwaterissoextremethatoseaweedscansurvive.Saltandosmosis(滲透作用)Innormalseawaterthecellsofaseaweedareinbalancewiththewateroutsideofthecells.Whensalinityintheexternalwatergoesdown,itcreatesanosmoticimbalancethatresultsinwaterbeingtakenupbythecells.Byloweringthecellularconcentrationsofionssuchaspotassium(鉀),sodium(鈉)anchloride(氯化物),aswellassugarsandorganiccompoundstorestoretheosmoticequilibriumtooneclosetothatbeforethesalinityhabeenreduced.Whenthesalinityoftheexternalwaterincreasesthereverseprocesstakeplace.Thehigherconcentrationofexternalsaltscauseswatertobelostfromthecells,againindirectproportiontotheincreaseinsalinity.Thecellshavetorestoretheosmoticbalancebytakingupions,orproducinggreatercellularconcentrationsofsugarsandorganiccompounds.SalinitytolerancevariesSeaweedshavedifferingcapabilitiesformakingtheseosmoticadjustmentsandhencevaryingtolerancestosalinitychanges.Ingeneral,seaweedsgrowinghigherontheshoretendtohavegreatertolerancethanspeciesfoundlowerontheshore.Manyintertidalseaweedsmaywithstandsalinitiesrangingfrom0-100,whereasmanysubtidalspeciesarekilledbyonlyslightchangesinsalinity,oratbesthavelimitedtoleranceofsalinitiesfrom20-50.Metabolicratesareseverelyreducedformostspeciesinextremelylowandhighsalinities.EffectoftemperatureonsalinestressTemperaturecanhaveasignificantinfluenceonhowwellseaweedssurvivesalinestress.Speciesnormallygrowwithinacertaintemperaturerangeandattemperaturesateitherextremeofthisrangetheabilitytowithstandsalinitystressisgenerallyreduced.5、TemperaturestressThegeographicaldistributionofseaweedspeciesislargelydictatedbytemperaturetolerance.Therearespeciesofseaweedthatrerestrictedtotropicalwaterswhichnarrowtemperaturetolerancescloseto30℃,whilespeciesintheAntarcticrarelysurvivetemperaturesabove13℃.Differencelifecyclestagesmayalsobesensitivetodifferenttemperaturerange.Temperaturetolerance,andthereforegeographicaldistribution,isalsomodifiedbytheabilityofaspeciestowithstandotherstresses,suchassalinityanddesiccation,especiallyatextremehighandlowtemperatures.SeasonaltemperaturechangesSeasonalchangesinwatertemperaturesarelargegradualandspeciesthatlivepermanentlysubmergedarenotoftenexposedtosuddenshiftsintemperature.Metabolicrateschangewiththeseseasonalvariationsduetotheeffectsoftemperatureonchemicalreactionrates,enzymemetabolismandbiophysicalprocesses.Atthelowerendofthetemperaturerangeforaparticularspecies,growthrateswillbeslowerthanathighertemperatures,andoftentherewillbetemperaturesatwhichgrowthisoptimal