The Potential Role of Roots and Rhizomes in Structuring Salt-Marsh Benthic Communities

136

139

A hybrid cordgrass, formed from a cross between Spartina alterniflora (Atlantic cordgrass) and S. foliosa (Pacific cordgrass), has recently spread within the intertidal zone of south San Francisco Bay. Sediment properties and macroinfaunal community structure were compared in patches invaded by Spartina hybrid and adjacent uninvaded patches at 3 sites in San Francisco Bay (2 tidal flats and 1 Salicornia marsh). We hypothesized that (1) sediments vegetated by Spartina hybrid would have reduced sediment grain size, higher organic matter content, lower redox potential, lower salinity and reduced microalgal biomass relative to adjacent unvegetated tidal flat sediments, and (2) that differences in the sediment environment would correspond to changes in the infaunal invertebrate community structure and feeding modes. We observed 75% lower total macrofaunal density and lower species richness in Spartina-vegetated sediments at Elsie Roemer (30 yr old invasion) than in an adjacent unvegetated tidal flat. This was due to lower densities of surface-feeding amphipods, bivalves, cirratulid and spionid polychaetes. The proportional representation of subsurface-deposit feeders was greater in Spartina patches than in unvegetated sediments. At a more recently invaded site (Roberts Landing; 15 yr invasion), Spartina patches differed from tidal flat sediments in composition, but not in abundance. Native (Salicornia) and Spartina patches exhibited similar sediment properties at San Mateo, where the Spartina hybrid invaded 8 to 10 yr earlier. No differences were detected in densities or proportions of surface-or subsurface-deposit feeders, but the proportion of carnivores/omnivores and grazers increased in the hybrid-invaded patches. These studies suggest that the invasive Spartina hybrid in south San Francisco Bay can have differing effects on sediment ecosystems, possibly depending on the location, age, or type of habitats involved.

Section: Salt Marsh Invasionmentioning

confidence: 98%

Benthic macrofaunal communities of three sites in San Francisco Bay invaded by hybrid Spartina, with comparison to uninvaded habitats

Neira

Levin²,

Grosholz³

2005

136

139

“…Our results are consistent with a similar threshold effect in that, compared to the mudflat, infauna were excluded from the below-ground structure of the S. anglica habitat, but not from the less dense native marsh habitat. In another Spartina species, Capehart & Hackney (1989) found that burrowing by the clam Polymesoda caroliniana was inhibited by S. alterniflora roots and rhizomes more than by other marsh vegetation. As a different explanation for inhibition of infauna, Neira et al (2006) showed that the canopy structure of the hybrid S. foliosa × alterniflora reduces flow and enhances deposition of fine sediment, leading to reduced oxygen levels in sediment.…”

Section: Mechanisms Of Spartina Anglica Impactmentioning

confidence: 99%

Impacts of the invasive grass Spartina anglica on benthic macrofaunal assemblages in a temperate Australian saltmarsh

Cutajar¹,

Shimeta²,

Nugegoda³

2012

Reported impacts of the invasive saltmarsh grass Spartina anglica on benthic macrofaunal assemblages around the world vary considerably, and there is little understanding of the reasons for this variation. We compared macrofaunal assemblages and sediment characteristics among patches of S. anglica and adjacent uninvaded habitats (bare mudflat and native saltmarsh) in southeastern Australia. Invaded patches showed reduced species richness (by 50%) and diversity compared to both uninvaded habitats. Macrofaunal abundance in S. anglica patches was also lower than in native marsh (by 60%), but not different from mudflat. There were no differences in biomass among habitats. Ordination clearly separated the species assemblage of invaded patches from uninvaded habitats, suggesting a unique community in the Spartina habitat. Molluscs and crustaceans were the most depleted in S. anglica patches, while the polychaete Nephtys australiensis was enhanced. Infauna and epifauna were both depleted in S. anglica, although the mechanisms for these impacts should differ. Burrowing by infauna in S. anglica patches was likely impeded by dense roots and rhizomes, because the below-ground plant biomass was 72% greater than in native saltmarsh. Epifauna were likely depleted in S. anglica patches due to shadinginduced inhibition of microphytobenthos growth, consistent with measured reductions of porewater salinity and increased mud content. Salinity and mud content were the sediment parameters that correlated most strongly with macrofaunal assemblage composition. These results, combined with a synthesis of published S. anglica impacts, suggest predictions of when S. anglica facilitates or inhibits macrofauna, considering infauna and epifauna separately.KEY WORDS: Spartina anglica · Invasive species · Cordgrass · Macrofauna · Saltmarsh · Estuary · Australia Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 464: [107][108][109][110][111][112][113][114][115][116][117][118][119][120] 2012 tralasia (Ranwell 1964, Chung 1983, Groenendijk 1986. They can invade unvegetated sediment flats as well as saltmarshes, seagrass beds, mangroves, and cobble beds (Bridgewater 1975, Dethier & Hacker 2005. By forming expansive monospecific swards with dense roots and rhizomes, invasive Spartina spp. are potent ecosystem engineers that severely impact native systems, e.g. by enhancing sediment accretion and stabilizing sediment against erosion (Blood 1995, Mudd et al. 2010, altering water flow (Bouma et al. 2005), and changing sediment characteristics such as grain size distribution (Whitlatch 1981, Edgar & Shaw 1993, pH and salinity (Chung 1990), water content (Cottet et al. 2007), oxygen levels (da Cunha Lana & Guiss 1991), organic matter (Peralta et al. 2008), and the biomass of subsurface root and rhizome material (Brusati & Grosholz 2006, Neves et al. 2010.These habitat-engineering effects can lead to changes in faunal communities such as displacement of species, colonization by new species, and ...

“…Levin & Talley (2000) cite a variety of studies where infauna density and density of various taxa were positively correlated with below-ground biomass of both constructed marshes (Levin & Talley 2000) and natural marshes (Osenga & Coull 1983, Rader 1984, Lana & Guiss 1992, Levin & Talley 2000. In some studies, however, several infauna taxa were negatively correlated with belowground biomass (Capehart & Hackney 1989, Levin & Talley 2000.…”

Section: Edaphic Factors and Successionmentioning

confidence: 99%

Long-term succession of benthic infauna communities on constructed Spartina alterniflora marshes

Craft

Sacco²

2003

Benthic infauna communities were characterized along a chronosequence (1 to 28 yr old) of 7 constructed Spartina alterniflora Loisel marshes and 7 natural (reference) marshes to identify patterns of succession following salt marsh creation. Infauna density and species richness (per 7.07 cm 2 core) achieved equivalence to comparable reference marshes within 8 yr following marsh creation. Taxa with dispersing larval stages (e.g. Streblospio benedicti, Capitella sp.) achieved equivalence within 3 yr following marsh creation. Taxa that lack a planktonic dispersal stage, such as tubificid oligochaetes and Manayunkia aesturina, were slower to develop. Densities of Manayunkia did not achieve equivalence to natural marshes until 8 yr after marsh creation. Twenty-five yr elapsed before oligochaete densities of constructed marshes were similar to natural marshes. In constructed marshes, densities of surface-deposit feeders, dominated by Streblospio and Manayunkia, achieved equivalence to natural marshes within 8 yr following marsh creation. Subsurface-deposit feeders, consisting mostly of oligochaetes, did not become equivalent to natural marshes for 25 yr. Predictable trajectories, described by an asymptotic increase over time, existed for total species, species richness, and surface-and subsurface-deposit feeders. Oligochaetes and Manayunkia, which produce nondispersing larvae, exhibited linear trajectories over time. In constructed marshes, total density and density of dominant taxa and trophic groups were strongly correlated with soil characteristics, especially organic C, N, bulk density and macro-organic matter (MOM, the living and dead root and rhizome mat). Non-linear regressions using soil organic C and MOM explained 38 to 40% of the variation in constructed marsh infauna density. The regressions suggest that a threshold of 0.5% soil organic C (500 g m -2 , 0 to 10 cm) and 500 g MOM m -2 (0 to 10 cm) is needed to support infauna densities comparable to densities found in natural marshes. Taxon richness of constructed marshes was more strongly related to vegetation characteristics, especially macro-organic matter quality (e.g. lignin) than soil characteristics. Development of benthic infauna communities following marsh construction requires longer than the 5 yr monitoring period required by many wetland mitigation plans, and as much as 25 yr are needed for some attributes (e.g. oligochaetes) to achieve equivalence.