Hurricane events facilitate the dominance of introduced invertebrate species in harbors

The coastal location and shallow depths of harbors suggest that fouling communities will be greatly affected by extreme weather events. Within fouling communities, ascidians are conspicuous animals and their sessile nature makes them ideal targets to assess community resilience. We established ascidian diversity and abundance at sixteen harbors and marinas along the coast of North Carolina (N.C., United States) a year after Hurricane Florence landfall (post-hurricane) in September 2018 at Wrightsville Beach (south N.C.) and compared results with those obtained in 2014 (pre-hurricane). The distribution and assemblage structure of native and introduced ascidians were analyzed using presence-absence and relative abundance similarity matrices. Both geographic location (north: less affected vs. south: more affected) and distance between harbors had a significant effect on ascidian assemblage composition in 2019, driven by differences in native species composition after the hurricane. Monthly photo-quadrats spanning pre- and post-hurricane periods at a harbor located where the hurricane made landfall revealed that all but one ascidian species disappeared from the docks after the hurricane. Recolonization occurred first for introduced species, and one year later, native species had not yet recovered to pre-hurricane levels. Further, we report the arrival of the globally introduced species Styela canopus and Diplosoma listerianum in N.C. Together, these data indicate that hurricane impacts may amplify regional differences in fouling communities by disproportionately affecting native members and facilitating the dominance of introduced species. This study significantly advances our understanding of the impact of hurricanes on fouling communities inhabiting harbors and the speed of natural recovery.

Automated summary

This study investigated the impact of hurricanes on ascidian diversity and abundance in harbors and marinas along the coast of North Carolina. The results showed that hurricanes significantly affected the composition of ascidian communities, particularly native species. Additionally, two globally introduced species were found in North Carolina's harbors. This study provides important insights into the effects of hurricanes on harbor marine organisms and their natural recovery.