Influence of habitat modification on the recovery of the environment and benthic community following the eradication of an invasive ecosystem engineer

Background/Question/Methods

Plants can variably affect the abundance and diversity of species in estuarine and marine communities by influencing temperature, light and flow regimes. With the efforts to eradicate the invasive hybrid Spartina (S. alterniflora x S. foliosa) in San Francisco Bay (CA, USA), there is a critical need to understand feedbacks between the invasion and recovery processes on the resident benthic communities. In 2013 we designed a field experiment to examine: 1) how variation in local abiotic conditions influence the rate of invertebrate recruitment and abundance of predators; 2) how invertebrate diversity influences the rate of habitat recovery post-hybrid eradication; and 3) how colonization of invertebrates feeds back to influence the physical and chemical environment. To address these questions and assess potential facilitation of other invasive species via hybrid modification of the physical environment, in June 2013 we deployed various structures including wooden dowels, shade screens and litter bags, and implemented aeration treatments and controls in the eradicated hybrid zone in Alameda, CA. Dowel and control plots were also established in the unvegetated mudflats, representing the putatively recovered zone in the area, to compare with a similar manipulation conducted in 2004 pre-hybrid eradication. 

Results/Conclusions

After 90 and 270 days, habitat type and treatment influenced the abundance and composition of infauna and epifauna as well as the accumulation of epibenthic microalgae, sediment organic matter, and soil temperature. As predicted, soil temperature and microalgae (chl-a) were lower in the dowel and shaded plots, indicating that the aboveground structure of the hybrid may reduce heat stress at the expense of decreasing algal food sources, with consequences for the composition of the invertebrate community. Similarly to findings from 2004, invertebrate diversity was higher in the dowel treatments; the abundance of associated invasive species (primarily the Eastern mud snail Illyanassa) increased dramatically in dowel plots across habitats. Treatment effects generally declined rapidly after structure removal across the two habitats but were more persistent in the hybrid zone, indicating legacy effects of the hybrid eradication with variable timescales for recovery within these communities.