An example of accelerated changes in current and future ecosystem trajectories: Unexpected rapid transitions in salt marsh vegetation forced by sea level rise

•Great sippewissett marsh vegetation has increasingly been altered in recent years.•Sea level rise is promoting conversion of short to taller spartina alterniflora.•Plant changes are promoting creek bank slumping, wrack strandings and habitat loss.•Models predict sea level rise will lead to submergence of the entire marsh.•Phragmites australis invasion is replacing species and preventing marsh migration.