Habitat‐dependent impacts of exotic plant invasions on benthic food webs in a coastal wetland

Abstract

AbstractExotic plants with wide ecological niches often invade multiple types of habitats, leading to homogenization of ecosystem structure and functions. How exotic plant invasions affect the structure and functions of benthic food webs in different habitats is poorly understood. We tested how Spartina alterniflora invasions affected benthic food webs in four contrasting types of habitat (Scirpus mariqueter marshes, Phragmites australis marshes, unvegetated tidal creeks, and bare tidal flats) in the Yangtze estuary. We examined distribution pattern of benthic macroinvertebrates, and documented the differences in basal resources of benthic food web by stable isotope analyses of δ13C and δ15N in different habitats. Our results showed that in unvegetated habitats, conversion of tidal creeks and bare tidal flats to exotic marshes following Spartina invasions significantly altered the functional composition of benthic food webs, which was driven partially by bottom‐up processes related to a consumer dietary shift from benthic organic matter to detritus (trophic effect) and by alteration in species composition related to habitat changes (nontrophic effect). In vegetated native habitats, while the replacement of native plants by Spartina consistently led to a shift in consumer diet from benthic organic matter to detritus, it did not significantly alter the functional composition of benthic food webs. These data suggested the relative importance of trophic and nontrophic effects of plant invasions on benthic food webs could vary with habitat structure (e.g., the presence of native vegetation). Our study provides new insights into the mechanisms underlying homogenization of ecosystem structure and functions by exotic plant invasions.