Influence of invasive Spartina growth stages on associated macrofaunal communities

Abstract

In coastal wetlands, invasive plants often act as ecosystem engineers altering flow, light and sediments which, in turn, can affect benthic animal communities. However, the degree of influence of the engineer will vary significantly as it grows, matures and senesces, and surprisingly little is known about how the influence of an ecosystem engineer varies with ontogeny. We address this issue on the tidal flats of San Francisco Bay where hybrid Spartina (foliosa · alterniflora) invaded 30 years ago. The invasion has altered the physico-chemical properties of the sediment habitat, which we predicted should cause changes in macrofaunal community structure and function. Through mensurative and manipulative approaches we investigated the influence of different growth stages of hybrid Spartina on macrobenthos and the underlying mechanisms. Cross-elevation sampling transects were established covering 5 zones (or stages) of the invasion, running from the tidal flat (pre-invasion) to an unvegetated dieback zone. Additionally, we experimentally removed aboveground plant structure in the mature (inner) marsh to mimic the 'unvegetated areas'. Our results revealed four distinct faunal assemblages, which reflected Spartina-induced changes in the corresponding habitat properties along an elevation gradient: a pre-invaded tidal flat, a leading edge of immature invasion, a center of mature invasion, and a senescing dieback area. These stages of hybrid Spartina invasion were accompanied by a substantial reduction in macrofaunal species richness and an increase in dominance, as well as a strong shift in feeding modes, from surface microalgal feeders to subsurface detritus/ Spartina feeders (mainly tubificid oligochaetes and capitellid polychaetes). Knowledge of the varying influence of plant invaders on the sediment ecosystem during different phases of invasion is critical for management of coastal wetlands.

Comparing biodiversity effects among ecosystem engineers of contrasting strength: macrofauna diversity in Zostera noltii and Spartina anglica vegetations

“…The only two annelid species that were abundantly present in the Spartina vegetation were the polychaete Heteromastus filiformis and oligochaetes. Both are small, sub-surface deposit feeding species, often reported in other studies to be common in Spartina vegetations (e.g., Neira et al 2005Neira et al , 2007. Particularly oligochaetes can reach high abundances in salt marshes, as they can live in the microhabitat created by the root system of the plants and are capable to feed upon Spartina detritus .…”

“…This allowed a significantly higher endofaunal species richness, abundance and biomass in the Spartina patch as compared to the Spartina marsh. Along a sequence of stages in the invasion of a hybrid Spartina, from tidal flat to dieback, Neira et al (2007) observed cascading changes in sediment conditions that led to a substantial reduction in macrobenthic species richness, increased dominance and a shift in feeding modes.…”

Lateral spread of invasive Spartina alterniflora in uncrowded environments

“…An adequate understanding of these two components of S. alterniflora spread will necessarily feature a blend of biological and stochastic mechanisms (Taylor et al 2004). S. alterniflora is a powerful ecosystem engineer (Neira et al 2007) that severely disrupts the trophic structure of intertidal estuarine lands (Levin et al 2006). The removal of S. alterniflora from Willapa Bay by mechanical and chemical treatments is reopening intertidal lands to shorebirds and waterfowl (Patten and O'Casey 2007) as well as to fishing and recreation (Murphy 2006).…”

Ecosystem Engineering Effects of Aster tripolium and Salicornia procumbens Salt Marsh on Macrofaunal Community Structure

“…Several studies reported a reduction of light under the canopy of S. foliosa and S. virginica marshes relative to unvegetated mudflats, resulting in a lower abundance of microalgae and a subsequent decline in surface deposit feeders, while subsurface feeding groups such as tubificid oligochaetes and capitellid polychaetes were less affected (Lana and Guiss 1992;Levin et al 2006;Neira et al 2007;Whitcraft and Levin 2007). In our study, we found no evidence that dominance of diatoms (here sampled from the upper 1 cm of sediment) was less in salt marsh than in unvegetated mudflats (Online Resources 1 and 2).…”

“…Some studies have demonstrated facilitation of other species or communities by salt marshes (Bruno et al 2003), while others demonstrated inhibition (Van Wesenbeeck et al 2007) or found no effect. The balance between facilitation and inhibition of benthic invertebrates by salt marsh plants may be tipped by the aboveground and belowground structure of the plant, and may therefore vary with plant species and successional stage (Brusati and Grosholz 2006;Neira et al 2007;Wang et al 2010).…”