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 SpartinaA.sulfide (μM)35302520151050B.600ammonium (μM)5004003002001000CTRL HET ILY MACCTRL HET ILY MACFig. 1: Results from Experiment 1 by treatment (CTRL=defaunated control,HET=Heteromastus filiformis, ILY=Ilyanassa obsoleta, andMAC=Macoma petalum). A. Porewater sulfide concentration. B. Porewaterammonium concentration. N=6 for all treatments.treatments, although <strong>the</strong>se differences were not significant(Fig. 2B and 2C).DISCUSSIONOur preliminary results suggest that under laboratoryconditions benthic macroinvertebrates can affect bothporewater ammonium concentrations and Spartinaalterniflora seedling growth. We found that both H.filiformis and M. petalum lowered porewater ammoniumconcentrations relative to controls, while surface grazers hadno obvious effect on porewater ammonium or sulfides.Benthic invertebrates can decrease porewater ammoniumand soluble sulfide concentrations by flushing porewatersolutes from sediments during burrow construction andirrigation (Aller 1982; Christensen et al. 2000) and bystimulating oxidation-reduction reactions (Pelegri andBlackburn 1995; Rysgaard et al. 2000), but <strong>the</strong> magnitude <strong>of</strong>change is limited by <strong>the</strong> depth <strong>of</strong> <strong>the</strong> burrow (e.g., Aller1982; Francois et al. 2002; Michaud et al. 2006).Despite <strong>the</strong> negative effect on porewater ammoniumconcentrations, H. filiformis appeared to have a positiveeffect on soluble sulfide concentrations although this wasnot confirmed statistically. Past work has demonstrated thatinvertebrates can increase sulfate reduction rates in marinesediments (Hansen et al. 1996). A variety <strong>of</strong> mechanismsincluding removal <strong>of</strong> inhibitory metabolites, redistribution <strong>of</strong>particles, secretion <strong>of</strong> labile mucus along burrow walls, andtranslocation <strong>of</strong> labile organic matter from <strong>the</strong> surface to <strong>the</strong>deeper sediment during feeding could be responsible forincreased anaerobic metabolism and sulfide productionA.B.C.change in leaf length (cm)biomass (g)biomass (g)121086420-2-4-60.100.080.060.040.020.000.120.100.080.060.040.020.00CTRL HET ILY MACCTRL HET ILY MACCTRL HET ILY MACFig. 2: Results from Experiment 2 by treatment (CTRL=defaunated control,HET=Heteromastus filiformis, ILY=Ilyanassa obsoleta, MAC=Macomapetalum). A. Change in leaf length <strong>of</strong> Spartina alterniflora seedlings. B.Aboveground biomass <strong>of</strong> S. alterniflora seedlings. C. Belowground biomass<strong>of</strong> S. alterniflora seedlings. * indicates treatment means that differsignificantly from each o<strong>the</strong>r (post-hoc Tukey, p< 0.05). N = 9 for eachtreatment.(Wheatcr<strong>of</strong>t et al. 1994; Marinelli and Boudreau 1996; Allerand Aller 1998). However, it is not clear which mechanismswould account for <strong>the</strong> positive effect <strong>of</strong> H. filiformis onsoluble sulfides or why H. filiformis would have oppositeeffects on ammonium and sulfide.Significant differences between treatments for change intotal leaf length suggest that <strong>the</strong> benthic community has <strong>the</strong>- 167 -