Ecological Outcomes of Invasive Rice Grass ( Spartina anglica ) Removal for Restoring Native Saltmarsh Vegetation and Fish Habitat Function

Abstract

Rice grass (Spartina anglica) is a widespread invasive species in south-east Australian saltmarshes and has been the target ofcontrol programmes since the 1990s, with purported benefits to native saltmarsh vegetation and fish habitat access. Recent large-scale rice grass control programmes in north-west Tasmania, funded by the Australian Government, provided an opportunityto monitor changes in vegetation and fish use before and after rice grass treatment. We undertook vegetation and fish surveysat two contrasting locations in Duck Bay, seeking to evaluate the potential benefits of the functional removal of this invasivespecies on the restoration of native saltmarsh vegetation and fish habitat function. At both sites, rice grass died back almostcompletely post-treatment and was replaced by native vegetation dominated by Sarcocornia quinqueflora. Fish surveys usingpop nets indicated that the plots where rice grass was removed had a significantly greater number of fish species and abundance.Species richness more than doubled (from 5 to 11 species) 3 years post-treatment and mean catch per net increased from ~2 to~45 individuals (~175 fish per 100 m 2 area), matching densities observed in undisturbed saltmarsh. At one site within a seascapeformerly dominated by expansive rice grass swards, fish were conspicuously absent from baseline surveys but reached 255 fishper 100 m 2 3 years post-treatment, with the catch dominated by yellow-eye mullet (Aldrichetta forsteri)—a species of commercialand recreational importance. Gut content analyses were done on 21 mullets caught at this site to offer insights into their use of thenative marsh as feeding habitats. Results indicate fish have likely fed on the restored native saltmarsh, confirming the recoveryof feeding as well as refuge functions. These findings provide novel insights into the nature and extent of saltmarsh ecosystemrecovery and fish habitat function, while also highlighting the potential benefits of invasive species control programmes.