<str<strong>on</strong>g>Proceedings</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> <str<strong>on</strong>g>Third</str<strong>on</strong>g> <str<strong>on</strong>g>Internati<strong>on</strong>al</str<strong>on</strong>g> <str<strong>on</strong>g>C<strong>on</strong>ference</str<strong>on</strong>g> <strong>on</strong> <strong>Invasive</strong> SpartinaChapter 3: Ecosystem Effects <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>Invasive</strong> SpartinaFig. 3: Native salt marsh communities <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> lower salt marsh being progressivelyinvaded by S. anglica cl<strong>on</strong>es, establishing seaward <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> nativevegetati<strong>on</strong>.Fig. 6: Spartina anglica col<strong>on</strong>izati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> a dolerite boulder beach at EastArm.Source: T. Colesa) b)Fig. 4: The intertidal z<strong>on</strong>e <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> Tamar at Paper Beach in 1956 (a), showing<str<strong>on</strong>g>the</str<strong>on</strong>g> sand and gravel substrate, and in 2004 (b) Spartina marsh extendingsome 140 m seaward.Fig. 7: Mature Spartina marsh at L<strong>on</strong>e Pine point, previously a DoleriteBoulder beach.Fig. 5: One <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> few remaining sandy intertidal z<strong>on</strong>es <str<strong>on</strong>g>of</str<strong>on</strong>g> Tamar, <str<strong>on</strong>g>the</str<strong>on</strong>g> upperintertidal z<strong>on</strong>e is typically sand and gravels grading into mudflat.4) Marine sands, limited to <str<strong>on</strong>g>the</str<strong>on</strong>g> lower estuary close to <str<strong>on</strong>g>the</str<strong>on</strong>g>mouth at Low head.VEGETATION OF THE INTERTIDAL ZONEPrior to <str<strong>on</strong>g>the</str<strong>on</strong>g> establishment <str<strong>on</strong>g>of</str<strong>on</strong>g> S. anglica, much <str<strong>on</strong>g>of</str<strong>on</strong>g><str<strong>on</strong>g>the</str<strong>on</strong>g> intertidal z<strong>on</strong>e, particularly in <str<strong>on</strong>g>the</str<strong>on</strong>g> mid Tamar, wasunvegetated. Enteromorpha and o<str<strong>on</strong>g>the</str<strong>on</strong>g>r algae were foundextensively <strong>on</strong> mudflats at all elevati<strong>on</strong>s within <str<strong>on</strong>g>the</str<strong>on</strong>g> intertidalz<strong>on</strong>e throughout <str<strong>on</strong>g>the</str<strong>on</strong>g> estuary. The absence <str<strong>on</strong>g>of</str<strong>on</strong>g> highernative salt marsh plants is probably due to <str<strong>on</strong>g>the</str<strong>on</strong>g>ir inabilityto col<strong>on</strong>ize <str<strong>on</strong>g>the</str<strong>on</strong>g> various intertidal geologies and promote<str<strong>on</strong>g>the</str<strong>on</strong>g> accumulati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> fine silts. Native salt marsh vegetati<strong>on</strong>,such as Sarcocornia quinqueflora, Sclerostegia arbuscula,and Suaeda australis is limited to a narrow fringe belowFig. 8: A prograding Spartina marsh, with <str<strong>on</strong>g>the</str<strong>on</strong>g> coalescence <str<strong>on</strong>g>of</str<strong>on</strong>g> isolatedclumps characteristic <str<strong>on</strong>g>of</str<strong>on</strong>g> Spartina col<strong>on</strong>izati<strong>on</strong>.<str<strong>on</strong>g>the</str<strong>on</strong>g> high water mark and in sheltered embayments, wi<str<strong>on</strong>g>the</str<strong>on</strong>g>xtensive salt marshes occurring <strong>on</strong>ly near Bell Bay, <strong>on</strong>relatively sandy substrates in <str<strong>on</strong>g>the</str<strong>on</strong>g> lower estuary (Fig. 3). Theability <str<strong>on</strong>g>of</str<strong>on</strong>g> S. anglica to establish at elevati<strong>on</strong>s lower thannative salt marsh plants provides a valuable competitiveadvantage. Spartina anglica has successfully col<strong>on</strong>izedin isolated clumps, coalesced to form laterally extensiveswards seaward <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> native salt marsh, and progressivelymove landward into <str<strong>on</strong>g>the</str<strong>on</strong>g> native vegetati<strong>on</strong>.- 131 -
Chapter 3: Ecosystem Effects <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>Invasive</strong> Spartina<str<strong>on</strong>g>Proceedings</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> <str<strong>on</strong>g>Third</str<strong>on</strong>g> <str<strong>on</strong>g>Internati<strong>on</strong>al</str<strong>on</strong>g> <str<strong>on</strong>g>C<strong>on</strong>ference</str<strong>on</strong>g> <strong>on</strong> <strong>Invasive</strong> SpartinaIMPACTS OF SPARTINA INVASIONThe introducti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> S. anglica to <str<strong>on</strong>g>the</str<strong>on</strong>g> Tamar Estuary hasbrought about a dramatic and rapid change to <str<strong>on</strong>g>the</str<strong>on</strong>g> physiography<str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> intertidal z<strong>on</strong>e, illustrated well at a photo pointestablished in 1956 at Paper beach (Fig. 4a and b). The col<strong>on</strong>izati<strong>on</strong><str<strong>on</strong>g>of</str<strong>on</strong>g> what was essentially a vacant niche has transformed<str<strong>on</strong>g>the</str<strong>on</strong>g> gently grading sandy intertidal z<strong>on</strong>es, as shown in Fig. 5,and hard rock intertidal z<strong>on</strong>es (Fig. 6) into laterally extensivemuddy terraces (Figs. 7 and 8).The ecological impacts <str<strong>on</strong>g>of</str<strong>on</strong>g> Spartina invasi<strong>on</strong> in temperateestuaries <str<strong>on</strong>g>of</str<strong>on</strong>g> South Eastern Australia are poorly understood.Studies <str<strong>on</strong>g>of</str<strong>on</strong>g> benthic macro-invertebrate communities in <str<strong>on</strong>g>the</str<strong>on</strong>g>Little Swanport Estuary, Tasmania suggest that Spartinasignificantly increases macro-invertebrate species richnessand total species abundance when compared to previouslyn<strong>on</strong>-vegetated intertidal areas (Hedge 1997). Additi<strong>on</strong>ally,macro-invertebrate communities <str<strong>on</strong>g>of</str<strong>on</strong>g> Spartina marshesshowed remarkable similarity to those <str<strong>on</strong>g>of</str<strong>on</strong>g> native salt marshes(Hedge and Kriwoken 2000). It is suggested <str<strong>on</strong>g>the</str<strong>on</strong>g>refore thatSpartina invasi<strong>on</strong> has provided a niche <str<strong>on</strong>g>of</str<strong>on</strong>g> s<str<strong>on</strong>g>of</str<strong>on</strong>g>t substrate anddense protecti<strong>on</strong>, favoring macro-invertebrates and somebirds such as <str<strong>on</strong>g>the</str<strong>on</strong>g> purple swamphen (Porphyrio porphyrio).It is likely that this subsequently caused a displacement <str<strong>on</strong>g>of</str<strong>on</strong>g>species that formerly inhabited or utilized <str<strong>on</strong>g>the</str<strong>on</strong>g> intertidal z<strong>on</strong>e.Species assemblage and utilizati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> intertidal z<strong>on</strong>e priorto Spartina is not well documented, but likely was relativelyrich in fish and bird species.DISCUSSIONThis paper has provided background for <str<strong>on</strong>g>the</str<strong>on</strong>g> researchproject that assessed <str<strong>on</strong>g>the</str<strong>on</strong>g> alterati<strong>on</strong> to <str<strong>on</strong>g>the</str<strong>on</strong>g> intertidal z<strong>on</strong>e <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>Tamar Estuary. Using transect based topographic surveys andcoring, <str<strong>on</strong>g>the</str<strong>on</strong>g> volume <str<strong>on</strong>g>of</str<strong>on</strong>g> material trapped under Spartina wascalculated to be 1,193,441 m 3 , comprised <str<strong>on</strong>g>of</str<strong>on</strong>g> approximately17% Spartina-derived organic matter and 83% silts andclays. Based <strong>on</strong> historical pr<str<strong>on</strong>g>of</str<strong>on</strong>g>iles, sedimentati<strong>on</strong> rates since<str<strong>on</strong>g>the</str<strong>on</strong>g> introducti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> S. anglica have been estimated at between8.7 and 52.4 millimeters per year (mm yr-1).From <str<strong>on</strong>g>the</str<strong>on</strong>g> analysis <str<strong>on</strong>g>of</str<strong>on</strong>g> 80 cores from four sites, Spartinatrappedsediment was found to c<strong>on</strong>tain levels <str<strong>on</strong>g>of</str<strong>on</strong>g> cadmium,copper, lead and zinc elevated above background levels.However, <str<strong>on</strong>g>the</str<strong>on</strong>g>se generaly were below trigger values <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>ANZECC/ARMCANZ (2000) interim sediment qualityguidelines. It is c<strong>on</strong>sidered unlikely that released sedimentswould impact <strong>on</strong> water quality or health <str<strong>on</strong>g>of</str<strong>on</strong>g> biota with respectto trace metals or organic c<strong>on</strong>taminati<strong>on</strong>.Behaviour <str<strong>on</strong>g>of</str<strong>on</strong>g> sediment with respect to erosi<strong>on</strong> rates,sediment redepositi<strong>on</strong> and causative hydrodynamics werealso m<strong>on</strong>itored within a test area from which Spartina coverwas removed. It has been dem<strong>on</strong>strated that <str<strong>on</strong>g>the</str<strong>on</strong>g> eradicati<strong>on</strong><str<strong>on</strong>g>of</str<strong>on</strong>g> S. anglica will result in elevati<strong>on</strong> loss from <str<strong>on</strong>g>the</str<strong>on</strong>g> Spartinamarsh surface at a rate six times greater than in vegetatedmarshes. The study assumed that this elevati<strong>on</strong> loss is causedby liberati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> sediments. The rate <str<strong>on</strong>g>of</str<strong>on</strong>g> elevati<strong>on</strong> loss orerosi<strong>on</strong> is likely to increase <strong>on</strong>ce <str<strong>on</strong>g>the</str<strong>on</strong>g> dead S. anglica root matdecomposes and <str<strong>on</strong>g>the</str<strong>on</strong>g> surface cohesi<strong>on</strong> and sediment-bindingcapacity is diminished. Elevati<strong>on</strong> loss increases by a factor <str<strong>on</strong>g>of</str<strong>on</strong>g>1.06 with every 10 m from <str<strong>on</strong>g>the</str<strong>on</strong>g> high water bank. Erosi<strong>on</strong> ratesin <str<strong>on</strong>g>the</str<strong>on</strong>g> outer 40 m <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> marsh were also significantly greaterthan <str<strong>on</strong>g>the</str<strong>on</strong>g> remainder <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> marsh at both sites, suggesting thata process o<str<strong>on</strong>g>the</str<strong>on</strong>g>r than S. anglica removal is c<strong>on</strong>tributing to thatretreat <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> lower marsh.Analysis <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>se interdisciplinary lines <str<strong>on</strong>g>of</str<strong>on</strong>g> inquiryhave allowed for a greater understanding <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>biogeomorphological resp<strong>on</strong>ses to restorati<strong>on</strong> attempts withinintertidal z<strong>on</strong>es and have provided a sound basis <strong>on</strong> which t<str<strong>on</strong>g>of</str<strong>on</strong>g>ormulate and implement future management <str<strong>on</strong>g>of</str<strong>on</strong>g> Spartina.Spartina eradicati<strong>on</strong> is recommended for <str<strong>on</strong>g>the</str<strong>on</strong>g> lower estuary(type 2 marshes) <strong>on</strong>ly, where trapped sediment volumesare significantly smaller and tidal flushing is greatest. Thiswould enable significant areas <str<strong>on</strong>g>of</str<strong>on</strong>g> sand/gravel intertidal z<strong>on</strong>esto recover and reduce <str<strong>on</strong>g>the</str<strong>on</strong>g> likelihood <str<strong>on</strong>g>of</str<strong>on</strong>g> fur<str<strong>on</strong>g>the</str<strong>on</strong>g>r downstreamexpansi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> Spartina swards. Retaining type 1 marshes in<str<strong>on</strong>g>the</str<strong>on</strong>g> upper estuary will prevent <str<strong>on</strong>g>the</str<strong>on</strong>g> remobilizati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> sedimentsthat c<strong>on</strong>tain <str<strong>on</strong>g>the</str<strong>on</strong>g> highest c<strong>on</strong>centrati<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> c<strong>on</strong>taminants, andwill retain <str<strong>on</strong>g>the</str<strong>on</strong>g> marshes for <str<strong>on</strong>g>the</str<strong>on</strong>g> ecological role <str<strong>on</strong>g>the</str<strong>on</strong>g>y currentlyperform.ACKNOWLEDGMENTSThis study was funded by <str<strong>on</strong>g>the</str<strong>on</strong>g> Australian ResearchCouncil Linkage Grant LP0214145, with support from <str<strong>on</strong>g>the</str<strong>on</strong>g>Department <str<strong>on</strong>g>of</str<strong>on</strong>g> Primary Industries and Water, Tasmania and<str<strong>on</strong>g>the</str<strong>on</strong>g> Rice Grass Advisory Group.REFERENCESANZECC/ARMCANZ, 2000. 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