<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> Spartinacollected from adjacent tidal flats and placed directly intoenclosures. A total <str<strong>on</strong>g>of</str<strong>on</strong>g> eight replicate blocks with fivetreatments per block were established (details in Neira et al.2006). All cages had a removable top for measurement <str<strong>on</strong>g>of</str<strong>on</strong>g>envir<strong>on</strong>mental variables such as temperature, salinity, lightpenetrati<strong>on</strong>, and redox potential. At <str<strong>on</strong>g>the</str<strong>on</strong>g> terminati<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>experiment (4 weeks), we recorded sediment temperature,salinity, light, and redox potential. For macr<str<strong>on</strong>g>of</str<strong>on</strong>g>aunalanalyses, we collected a single-core (18.1 cm 2 , 0-6 cm) from<str<strong>on</strong>g>the</str<strong>on</strong>g> center <str<strong>on</strong>g>of</str<strong>on</strong>g> each experimental and c<strong>on</strong>trol enclosure. Aftersieving <strong>on</strong> a 0.3 mm mesh sieve, retained organisms weresorted, identified to species level and counted. An additi<strong>on</strong>alcore was taken for analysis <str<strong>on</strong>g>of</str<strong>on</strong>g> organic matter c<strong>on</strong>tent.RESULTSRelative water flow: Overall relative water velocity wasreduced by more than 50% in hybrid Spartina habitatrelative to unvegetated tidal flats. The plant canopy reducedmean flow speed from 3-4 cm s -1 in unvegetated tidal flat toless than 0.7 cm per sec<strong>on</strong>d (s -1 ) in vegetated patches. Waterflux as estimated by mass loss <str<strong>on</strong>g>of</str<strong>on</strong>g> gypsum cards (pooledacross <str<strong>on</strong>g>the</str<strong>on</strong>g> three measurement periods) was 14.5 ±0.9 g d -1 in<str<strong>on</strong>g>the</str<strong>on</strong>g> tidal flat and 6.6 ±0.5 g d -1 in <str<strong>on</strong>g>the</str<strong>on</strong>g> vegetated patches(paired t test, P < 0.0001, Table 1). Gypsum cards placed <strong>on</strong><str<strong>on</strong>g>the</str<strong>on</strong>g> tidal flat were str<strong>on</strong>gly eroded which revealed <str<strong>on</strong>g>the</str<strong>on</strong>g>dynamic and variable nature <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> water regime at ElsieRoemer.Larval flux: The hybrid Spartina canopy structurereduced larval flux relative to <str<strong>on</strong>g>the</str<strong>on</strong>g> unvegetated tidal flat.After two m<strong>on</strong>ths, <str<strong>on</strong>g>the</str<strong>on</strong>g> number <str<strong>on</strong>g>of</str<strong>on</strong>g> barnacles per shell wasnearly 10 times higher in tidal flats (32.1 ±6.4) than inSpartina hybrid habitat (3.6 ±1.3 (paired t test, P = 0.022,Table 1).Sediment depositi<strong>on</strong>: We recorded higher rates <str<strong>on</strong>g>of</str<strong>on</strong>g>sedimentati<strong>on</strong> in <str<strong>on</strong>g>the</str<strong>on</strong>g> hybrid Spartina habitat (20.4 mg cm -2d -1 ) than <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> unvegetated tidal flat (14.2 mg cm -2 d -1 )(paired t test, P = 0.005). The fine sediment fracti<strong>on</strong> (< 63μm) deposited <strong>on</strong> traps placed in <str<strong>on</strong>g>the</str<strong>on</strong>g> hybrid habitat wasgreater than 45%, but was less than 13% in tidal flats (Table1).Animal transport: We found nearly two times as manyanimals entrained in traps deployed in <str<strong>on</strong>g>the</str<strong>on</strong>g> hybrid Spartinahabitat (4.9 ±0.6 per individual trap per day (ind trap -1 d -1 ))than <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> unvegetated tidal flats (2.6 ±0.5 ind trap -1 d -1 )(paired t test, P = 0.019, Table 1. In additi<strong>on</strong>, <str<strong>on</strong>g>the</str<strong>on</strong>g> faunalassemblage differed between habitats (ANOSIM, P =0.013). This may be <str<strong>on</strong>g>the</str<strong>on</strong>g> result <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> canopy structureslowing water flow and reducing turbulence, thus allowinggreater depositi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> animals in <str<strong>on</strong>g>the</str<strong>on</strong>g> collectors placed in <str<strong>on</strong>g>the</str<strong>on</strong>g>vegetated patches.Sediment properties: Most <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> alterati<strong>on</strong>s weresimilar to those found during mensurative studies performedpreviously at this site (Neira et al. 2005). Relative tounvegetated tidal flat, sediments <str<strong>on</strong>g>of</str<strong>on</strong>g> unclipped hybridSpartina -vegetated patches were muddier (48.6% vs 10.7%Table 1. Summarized results <str<strong>on</strong>g>of</str<strong>on</strong>g> manipulative experiments performed at Elsie RoemerEnvir<strong>on</strong>ment variables / Macr<str<strong>on</strong>g>of</str<strong>on</strong>g>auna Tidal flat Spartina hybrid(Mean ± 1 SE)Water columnWater moti<strong>on</strong> (weight loss <str<strong>on</strong>g>of</str<strong>on</strong>g> gypsum cards) (g d -1 ) 14.5 (±0.9) 6.6 (±0.5)Water speed (cm s -1 ) 3-4 0.3-0.7Larval flux (barnacle shell -1 ) 32.1 (±6.4) 3.6 (±1.3)Sediment depositi<strong>on</strong> rate (mg cm -2 d -1 ) 14.2 (±) 20.4 (±)TOM <str<strong>on</strong>g>of</str<strong>on</strong>g> deposited sediment (%) 1.9 (±0.4) 13.9 (±0.8)Mud c<strong>on</strong>tent (
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> Spartinaobserved in unmanipulated sediments <str<strong>on</strong>g>of</str<strong>on</strong>g> hybrid Spartinahabitat relative to tidal flats (Neira et al. 2005).Predati<strong>on</strong>: The sediment surface in cages c<strong>on</strong>tainingcrabs was disturbed with obvious depressi<strong>on</strong>s created byforaging crabs. The sediments also had lower organic matterand chlorophyll a c<strong>on</strong>tent relative to those cages withoutcrabs. No differences were found in salinity, temperatureand light penetrati<strong>on</strong> between treatments. Total macr<str<strong>on</strong>g>of</str<strong>on</strong>g>aunaldensity in experimental enclosures c<strong>on</strong>taining crabs was 2.2times lower than those without crabs. Density <str<strong>on</strong>g>of</str<strong>on</strong>g> selectedsurface-feeding species such as G. jap<strong>on</strong>ica, Corophium spp.and G. gemma declined by 57%, 87% and 67%, respectivelyin enclosures with crabs. O<str<strong>on</strong>g>the</str<strong>on</strong>g>r taxa that also declined wereSphaerosyllis californiensis, turbellarians, a juvenilearenicolid species and juvenile capitellids (Neira et al.2006).DISCUSSION AND CONCLUSIONOur results show that compositi<strong>on</strong> and structure <str<strong>on</strong>g>of</str<strong>on</strong>g> tidalflat macr<str<strong>on</strong>g>of</str<strong>on</strong>g>aunal benthic communities are str<strong>on</strong>glyinfluenced by hybrid Spartina invasi<strong>on</strong>. Specifically, wefound that Spartina reduces water flow. These, in turn,influence flux <str<strong>on</strong>g>of</str<strong>on</strong>g> recruiting larvae, transport <str<strong>on</strong>g>of</str<strong>on</strong>g> o<str<strong>on</strong>g>the</str<strong>on</strong>g>rbenthos, <str<strong>on</strong>g>the</str<strong>on</strong>g> input <str<strong>on</strong>g>of</str<strong>on</strong>g> organic matter, and sedimentdepositi<strong>on</strong>.These physical changes interacted with chemicalchanges including increased porewater sulfidec<strong>on</strong>centrati<strong>on</strong>s and more negative redox potential levels(Neira et al. 2006, 2007). We also found changes in growthand survival via predati<strong>on</strong> (Neira et al. 2006) and foodavailability (Levin et al. 2006), which can play key, possiblysynergistic, roles in structuring Spartina-invadedecosystems. The presence <str<strong>on</strong>g>of</str<strong>on</strong>g> hybrid Spartina in open tidalflats exerts a str<strong>on</strong>g influence <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> compositi<strong>on</strong> anddistributi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> benthic invertebrates in Elsie Roemer (Neiraet al. 2005, 2006).The reducti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> macr<str<strong>on</strong>g>of</str<strong>on</strong>g>aunal densities in hybridSpartina relative to <str<strong>on</strong>g>the</str<strong>on</strong>g> naturally unvegetated tidal flats isc<strong>on</strong>sistent with results for invasive S. anglica (Jacks<strong>on</strong> 1985)and S. alterniflora in o<str<strong>on</strong>g>the</str<strong>on</strong>g>r estuaries (Zipperer 1996), butc<strong>on</strong>trasts with existing paradigms about positive vegetati<strong>on</strong>effects <strong>on</strong> marine macrobenthos (e.g., Hedge and Kriwoken2000; Netto and Lana 1999). In additi<strong>on</strong>, not all systemsresp<strong>on</strong>d in <str<strong>on</strong>g>the</str<strong>on</strong>g> same way to <str<strong>on</strong>g>the</str<strong>on</strong>g> hybrid Spartina invasi<strong>on</strong>(Neira et al. 2005). For example, at o<str<strong>on</strong>g>the</str<strong>on</strong>g>r sites such asRoberts Landing (15-year invasi<strong>on</strong>), hybrid Spartina habitatdiffered from tidal flat sediments in compositi<strong>on</strong> but notabundance. At a third San Francisco Bay site, in San Mateo,where a Salicornia marsh is being invaded (8-10 years),sediment properties were similar, and no differences weredetected in densities or proporti<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> surface- orsubsurface-deposit feeders, but <str<strong>on</strong>g>the</str<strong>on</strong>g> proporti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g>carnivores/omnivores and grazers increased in <str<strong>on</strong>g>the</str<strong>on</strong>g> hybridSpartina habitat (Neira et al. 2005). At Elsie Roemer, most<str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> species shown to have reduced density in hybridSpartina-invaded tidal flats are surface-feeding animals,such as amphipods (Corophium spp., Grandidierellajap<strong>on</strong>ica) bivalves (Gemma gemma) and polychaetes(Tharyx spp.). Thus, where hybrid Spartina has invaded tidalflats it is likely to cause not <strong>on</strong>ly changes in <str<strong>on</strong>g>the</str<strong>on</strong>g> habitatstructure, but also to shift macr<str<strong>on</strong>g>of</str<strong>on</strong>g>aunal feeding modes fromsurface-microalgae feeders to subsurface detritivores. Theshift from surface-feeding taxa can have negative ecologicalimplicati<strong>on</strong>s for higher trophic levels. Birds and fishesdepend more <strong>on</strong> larger, surface-feeding species (Simenstadand Thom 1995), which decline in abundance with <str<strong>on</strong>g>the</str<strong>on</strong>g>invasi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> Spartina. However, <str<strong>on</strong>g>the</str<strong>on</strong>g> full impact <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>Spartina invasi<strong>on</strong> <strong>on</strong> birds and fishes in San Francisco Bayhas yet to be measured.We can c<strong>on</strong>clude that <str<strong>on</strong>g>the</str<strong>on</strong>g> invasi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> hybrid Spartinahas resulted in substantial changes in benthic communitiesby modifying <str<strong>on</strong>g>the</str<strong>on</strong>g> physical and chemical envir<strong>on</strong>ment.However, we find that not all ecosystems resp<strong>on</strong>d identicallyfollowing hybrid Spartina invasi<strong>on</strong> in San Francisco Bay.Hybrid Spartina can have differing and complex effects <strong>on</strong><str<strong>on</strong>g>the</str<strong>on</strong>g> sediment envir<strong>on</strong>ment and associated fauna depending<strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> locati<strong>on</strong>, type <str<strong>on</strong>g>of</str<strong>on</strong>g> habitat involved, age <str<strong>on</strong>g>of</str<strong>on</strong>g> invasi<strong>on</strong>,and local hydrodynamics. The processes underlying <str<strong>on</strong>g>the</str<strong>on</strong>g>variable resp<strong>on</strong>ses to Spartina invasi<strong>on</strong>, and <str<strong>on</strong>g>the</str<strong>on</strong>g> differentrates <str<strong>on</strong>g>of</str<strong>on</strong>g> recovery following invasi<strong>on</strong>, are factors that shouldbe c<strong>on</strong>sidered in planning for Spartina eradicati<strong>on</strong>.ACKNOWLEDGMENTSWe acknowledge G. Mendoza, R. Blake, C. Tyler, S.Maezumi, C. Whitcraft, U. Mahl, E. Brusati, N. Rayl, N.Christensen, P. McMillan, P. Colombano, J. G<strong>on</strong>zalez, S.Nort<strong>on</strong>, and D. Chiang who kindly assisted in experimentsetup, sample collecti<strong>on</strong> in <str<strong>on</strong>g>the</str<strong>on</strong>g> field and lab analysis. We aregrateful to C. Tyler who provided sulfide data. We thank C.Nordby, E. Brusati and R. Blake for providing compliancewith California Clapper Rail permit requirements. Supportwas provided by Nati<strong>on</strong>al Science Foundati<strong>on</strong>Biocomplexity Program (DEB 0083583) to L.A.L. andE.D.G.A full manuscript <str<strong>on</strong>g>of</str<strong>on</strong>g> this study was published inEcological Applicati<strong>on</strong>s (Neira et al. 2006); see referencebelow.REFERENCESAyres, D.R., D.R. Str<strong>on</strong>g and P. Baye. 2003. Spartina foliosa(Poaceae) - A comm<strong>on</strong> species <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> road to rarity. Madroño50:209-213.Ayres, D.R., D.L. Smith, K. Zaremba, S. Klohr and D.R. Str<strong>on</strong>g.2004. Spread <str<strong>on</strong>g>of</str<strong>on</strong>g> exotic cordgrasses and hybrids (Spartina sp.) in<str<strong>on</strong>g>the</str<strong>on</strong>g> tidal marshes <str<strong>on</strong>g>of</str<strong>on</strong>g> San Francisco Bay. Biological Invasi<strong>on</strong>s6:221-231.Buchanan, J.B. 1984. Sediment analysis. 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