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 1: Spartina BiologyMECHANISMS OF SULFIDE AND AOXIA TOLERANCE IN SALT MARSH GRASSESIN RELATION TO ELEVATIONAL ZONATIONB.R. MARICLE 1,2 AND R.W. LEE 11 School <strong>of</strong> Biological Sciences, Washington State University, Pullman, WA 99164-42362 Present address: Department <strong>of</strong> Biological Sciences, Fort Hays State University, Hays, KS 67601-4099; brmaricle@fhsu.eduSharply-defined ecotones commonly separate species living in high intertidal and low intertidalestuarine zones. Low intertidal regions are characterized by anoxic sediments and toxic levels <strong>of</strong>hydrogen sulfide. These conditions exclude high marsh species. In contrast, low marsh species arebelieved to possess physiological adaptations to resist <strong>the</strong> anoxia and sulfide. However, <strong>the</strong>seadaptations are poorly understood. One <strong>of</strong> <strong>the</strong> most important characteristics <strong>of</strong> waterloggedsediments is <strong>the</strong> lack <strong>of</strong> oxygen. Many wetland plants have been shown to transport atmosphericoxygen internally to support respiration in submerged tissues. This ability may allow plant survivalin low intertidal marsh areas and is <strong>of</strong>ten implicated as a factor in determining species zonation inestuaries. In this study, oxygen transport and metabolic characteristics related to anoxia toleranceand rhizosphere oxidation were investigated in <strong>the</strong> emergent estuarine species Spartina alterniflora,S. anglica, S. densiflora, S. patens, and Distichlis spicata (Poaceae). Plants were grown ingreenhouse experiments under simulated estuarine conditions. All species showed a strong ability torespire anaerobically. The high intertidal marsh species S. densiflora, S. patens, and D. spicata werefound to have high aerobic respiration rates, low oxygen transport rates, and an apparent highsensitivity to sulfide. The low intertidal marsh species S. alterniflora and S. anglica had loweraerobic respiration rates, moderate to high oxygen transport rates, and a lower sensitivity to sulfide.Spartina anglica appeared to have <strong>the</strong> greatest ability to transport oxygen and was more resistant tomudflat-related stressors compared to <strong>the</strong> o<strong>the</strong>r plants in this study. Evidence is presented thataerobic respiration rates and sulfide sensitivity may be important factors for differences in estuarinezonation between species.Keywords: Distichlis spicata, hypoxia, oxygen transport, respiration, sediment, Spartina, sulfideINTRODUCTIONThe introduction <strong>of</strong> four species <strong>of</strong> Spartina grasses(Poaceae) into Washington estuaries has led to manydevastating ecological and economic impacts. Nearly 8,100hectares (ha) <strong>of</strong> intertidal mudflat in Willapa Bay,Washington, USA, has been affected by introduced S.alterniflora (Hedge et al. 2003). Similarly, S. anglica wasintroduced in nor<strong>the</strong>rn Puget Sound, Washington in 1961 topresvent shoreline erosion, but quickly spread via tidalcurrents and now affects over 3,300 ha in <strong>the</strong> Puget Soundarea (Hacker et al. 2001). O<strong>the</strong>r Spartina introductions intoWashington estuaries include Spartina densiflora Brong.(WSDA news release 11 Jan 2002) and S. patens (Aiton)Muhl. (Frenkel 1987). These populations remain small andare closely monitored to prevent spread.Introduced Spartina flourishes in West Coast estuariesbecause it can occupy an open niche: low intertidal mudflatsand tidal channels characterized by highly reducingconditions (an oxidation reduction potential less than -300millivolts [Eh