Introduced Spartina anglica modifies fish habitat in southern temperate succulent saltmarshes

Vegetation changes in saltmarsh habitat can influence fish assemblages and abundance. In Tasmania, Australia, mid-latitude succulent saltmarsh communities have been invaded by the introduced tall grass, Spartina anglica. Eradication efforts have been ongoing since the 1990s with purported benefits for fish access to intertidal foraging grounds, but a lack of knowledge of the impact of S. anglica on fish limits understanding of the benefits and effectiveness of native habitat restoration. Here, we investigate whether fish assemblages in native saltmarshes and non-native S. anglica grassland differ in species diversity, fish abundance, and size class distribution. We used buoyant pop nets to sample fishes in Sarcocornia quinqueflora herbland and S. anglica grassland swards at three sampling stations in northwest Tasmania. Very few individuals and low species diversity were recorded in both vegetation types at the sampling station with the most well-established S. anglica infestation. Elsewhere, richness and diversity were higher in S. quinqueflora herbland. Overall fish abundance was higher in S. quinqueflora than in S. anglica, with a very strong effect at one sampling station. Fewer small individuals of the numerically dominant Atherinosoma microstoma were recorded in S. anglica, potentially indicating impaired nursery function. Our results provide important insights for S. anglica control, as we are the first to demonstrate a relationship between S. anglica presence and fish characteristics in southern Australian saltmarsh. These results indicate that S. anglica control is valuable for fish conservation. An extension of our research to document the effects of S. anglica removal on fishes is desirable.