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

Abstract

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 ...

Early Invasion of Common Cordgrass (Spartina Anglica) Increases Belowground Biomass and Decreases Macrofaunal Density and Diversity in a Tidal Flat Marsh

“…Even within such a short period, the impact of S. anglica on macrofaunal diversity and density was su ciently strong to produce signi cant effects. To some extent, these results are consistent with previous ndings obtained in a temperate Australian salt marsh (Cutajar et al 2012), and in Wenzhou Bay, China (Get et al 2012). Cutajar et al (2012) reported that invaded patches showed a 50% reduction in species richness, and reduced diversity, compared to two uninvaded habitats.…”

Sediment Type Affects Competition between a Native and an Exotic Species in Coastal China

“…Spartina is a rhizomatous perennial grass that is highly invasive in German, Australian, Irish estuarine mudflats, sand flats and salt marshes 35 51 52 . The plant may reach a height of 50–100 cm, and its leaf blades are flat or in-rolled and 5–12 mm wide.…”

Control and consequences of Spartina spp. invasions with focus upon San Francisco Bay

“…With vague rationalizations of possible value, S. anglica was introduced to Australia during the first half of the twentieth century. Introductions ceased by 1962, and concerted control with herbicides has been practiced in recent decades (Cutajar et al 2012). The most recent large invasion stems from the purposeful introduction of S. alterniflora in China, where the consequences are beginning to be assessed (Strong and Ayres 2013).…”