tpo综合写作26第一篇：tpo综合写作26综合写作26ReadingThezebramussel,afreshwatershellfishnativetoEasternEurope,haslongbeenspreadingoutfromitsoriginalhabitatsandhasnowreachedpartsofNorthAmerica.TherearereasonstobelievethatthisinvasioncannotbestoppedandthatitposesaseriousthreattofreshwaterfishpopulationsinallofNorthAmerica.First,thehistoryofthezebramussels’spreadsuggeststhattheinvasionmightbeunstoppable.Itisaprimeexampleofaninvasionmadepossiblebyhumantransportation.Fromthezebramussel’soriginalhabitatsinEasternEurope,shipshelpedspreaditoutalongnewcanalsbuilttoconnectEurope’swaterways.Themusselcanattachitselftoaship’sbottomorcansurviveinthewater—called“ballastwater“—thattheshipneedstotakeontoproperlybalanceitscargo.Bytheearlynineteenthcentury,themusselhadspreadtothewholeofEurope.ItwaslatercarriedtotheeastcoastofNorthAmericaintheballastwaterofshipstravelingfromEurope.ThewayshipshavespreadthezebramusselinthepaststronglysuggeststhatthespecieswillsooncolonizeallofNorthAmerica.Moreover,oncezebramusselsarecarriedtoanewhabitat,theycandominateit.Theyareahardyspeciesthatdoeswellunderavarietyofconditions,andtheyhaveahighrateofreproduction.Mostimportant,however,zebramusselsoftenhavenopredatorsintheirnewhabitats,andspecieswithoutnaturalpredatorsarelikelytodominatetheirhabitats.Finally,zebramusselsarelikelytocauseadeclineintheoverallfishpopulationinhabitatswheretheybecomedominant.Themusselsareplanktoneaters,whichmeanthattheycompeteforfoodwithmanyfreshwaterfishspecies.Summarizethepointsmadeinthelecture,beingsuretoexplainhowtheysupport/contradictspecificpointsmadeinthereadingpassage.ListeningNarratorNowlistentopartofalectureonthetopicyoujustreadabout.ProfessorContrarytowhatyoujustread,therearewaystocontrolthezebramussels’spread.What'smore,itisnotsoclearthatthemusselisaseriousthreattofishpopulations.True,thespreadofzebramusselscouldn'tbecontrolledinthepast,butthat'sbecausepeopledidn'thaveenoughknowledge.Infact,thereareeffectivewaystostopshipsfromcarryingthemusselstonewlocations.Here'sanexample.Thewayze