Proceedings of the Third International Conference on Invasive ...

<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive SpartinaChapter 3: Ecosystem Effects <strong>of</strong> Invasive SpartinaB.A. 15 N (‰) 15 N (‰)1815121816141296China CampHemigrapsusBalanus CarcinusBalanus-22 -20 -18 -16 -14 -12 13 C (‰)BalanusCarcinusUrosalpinxAlameda10-20 -18 -16 -14 -12 13 C (‰)hybridCarcinusHemigrapsusS. foliosa mudflatCarcinusUrosalpinxBalanushybridSpartinamudflatS. foliosaFig. 3. Stable Isotope Results. Crabs (H. oregonensis, C. maenas) at ChinaCamp showed possible incorporation <strong>of</strong> S. foliosa (A), while nei<strong>the</strong>r C.maenas nor oyster drills (Urosalpinx cinerea) at Alameda appeared to incorporatehybrid Spartina (B).rhizomes <strong>of</strong> hybrid Spartina pre-empt space needed byinfauna so that invertebrates are replaced by plant material.Our stable isotope results show that <strong>the</strong> high biomassproduced by hybrid Spartina does not translate intoincreased incorporation <strong>of</strong> Spartina in <strong>the</strong> infaunal food web.Hybrid Spartina’s thick stems may require a longer time todecompose than <strong>the</strong> thinner stems <strong>of</strong> S. foliosa. As a result,carbon is held in hybrid Spartina ra<strong>the</strong>r than transferred tohigher trophic levels.The change from <strong>the</strong> relatively open canopy <strong>of</strong> S.foliosa to <strong>the</strong> more denser stems <strong>of</strong> hybrid Spartina mayhave indirect consequences for o<strong>the</strong>r primary producers thatare important to estuarine food webs, especially benthicmicroalgae. On <strong>the</strong> Atlantic coast, microalgal productionwas lower underneath <strong>the</strong> canopy <strong>of</strong> tall form S. alterniflorathan under <strong>the</strong> shorter dwarf form (Sullivan and Currin2000), suggesting a potential decrease in microalgalproduction in nor<strong>the</strong>rn California as hybrid Spartina replacesshorter S. foliosa.Comparing effects <strong>of</strong> native S. foliosa and hybridSpartina may help resource managers predict <strong>the</strong> impact ifhybrid Spartina establishes populations in coastal bays north<strong>of</strong> San Francisco, while data from S. foliosa marshes mayprovide reference information for evaluating restorationprojects. Infauna are major food sources for shorebirds andnative fishes, recycle carbon by breaking down plantdetritus, and move sediment by bioturbation and suspensionfeeding (Levin et al. 2001). Therefore, if replacement <strong>of</strong> S.foliosa with hybrid Spartina leads to relatively lowerinfaunal densities, consequences for <strong>the</strong> food web may reachbeyond <strong>the</strong> direct structural changes caused by <strong>the</strong> plants.ACKNOWLEDGMENTSWe thank <strong>the</strong> following for <strong>the</strong>ir assistance with thisproject. Funding: Canon National Parks Science ScholarsProgram (E.B.), University <strong>of</strong> California CoastalEnvironmental Quality Initiative (E.B.), UC-Davis PublicService Research Group (E.B.), Bodega Marine Laboratory,Sigma Xi (E.B.), Jastro Shields grant (E.B.), NSFBiocomplexity Program (DEB-0083583) (E.G.). Field andlab assistance: D. Ayres, L. Harris, C. Black, R. Blake, A. C.Tyler, N. Rayl, S. Norton, T. Dillon, and J. McCoy. Siteaccess: Point Reyes National Seashore (permit PORE-2001-SCI-0026), Gulf <strong>of</strong> <strong>the</strong> Farallones National MarineSanctuary (permit GFNMS-2001-004), Cypress GrovePreserve, China Camp State Park, Marin County OpenSpace District, and East Bay Regional Park District.REFERENCESBrusati, E.D., and E.D. Grosholz. 2006. Native and introducedecosystem engineers produce contrasting effects on estuarineinfaunal communities. Biological Invasions 8:683-695.Brusati, E.D., and E.D. Grosholz. 2009. Does <strong>the</strong> invasion <strong>of</strong>hybrid cordgrass change estuarine food webs? BiologicalInvasions 11:917-926.Capehart, A.A., and C.T. Hackney. 1989. The potential role <strong>of</strong>roots and rhizomes in structuring salt-marsh benthiccommunities. Estuaries 12:119-122.Daehler, C.C., and D.R. Strong. 1996. Status, prediction, andprevention <strong>of</strong> introduced cordgrass Spartina spp. invasions inPacific estuaries, USA. Biological Conservation 78:51-58.Levin, L.A., D.F. Boesch, A. Covich, C. Dahm, C. Erseus, K.C.Ewel, R.T. Kneib, A. Moldenke, and J.M. Weslawski. 2001. Thefunction <strong>of</strong> marine critical transition zones and <strong>the</strong> importance <strong>of</strong>sediment biodiversity. Ecosystems 4:430-451.Neira, C., L.A. Levin, and E.D. Grosholz. 2005. Benthicmacroalgal communities <strong>of</strong> three sites in San Francisco Bayinvaded by hybrid Spartina with comparison to uninvadedhabitats. Marine Ecology Progress Series 292:111-126.Netto, S.A., and P.C. Lana. 1999. The role <strong>of</strong> above- and belowgroundcomponents <strong>of</strong> Spartina alterniflora (Loisel) and detritusbiomass in structuring macrobenthic associations <strong>of</strong> ParanaguaBay (SE, Brazil). Hydrobiologia 400:167-177.Sullivan, M.J., and C.A. Currin. 2000. Community structure andfunctional dynamics <strong>of</strong> benthic microalgae in salt marshes. In:Weinstein, M.P., and D.A. Kreeger. Concepts and Controversiesin Tidal Marsh Ecology. pp. 81-106. Kluwer AcademicPublishers. Dordrecht, The Ne<strong>the</strong>rlands.- 163 -