A managed realignment in the upper Bay of Fundy: Community dynamics during salt marsh restoration over 8 years in a megatidal, ice-influenced environment

Salt marshes are ecologically and globally vital ecosystems. Unfortunately, world-wide salt marsh loss has been extensive, and until recently there has been little effort to undo the loss of ~30,500 ha of salt marshes in Bay of Fundy, Canada, since European colonization. To better understand salt marsh restoration in the upper Bay of Fundy, we monitored sediment deposition and community dynamics in 2 managed realignment salt marsh restoration sites and 2 reference sites from 1 y pre-breach to 8 y post-breach in Aulac, New Brunswick. Because of the initial elevational disparity (~2 m) between site types, substantial amounts of sediment were deposited immediately after breaching the old dike (>50 cm in some locations). After 7–8 y, mean sediment deposition was 34–67 cm in the restoration sites, and 6 cm in a reference site. To date, we identified three stages of vegetative community succession: (i) rapid deposition of unconsolidated sediment and loss of terrestrial vegetation, but Spartina pectinata remained (1 y post-breach), (ii) colonization and spread of S. alterniflora and loss of S. pectinata (2–5 y post), and (iii) high percent cover and decreased spatial variability of S. alterniflora (mean stem density: 345 stems m−2, 6–8+ y post). We expect the fourth stage of vegetative community succession will be defined by spread of S. patens throughout restoration sites. Invertebrate community on emergent marsh and water column community in salt pools were variable and lagged behind vegetative community. Our study reported the first managed realignment in Maritime Canada, and the first such realignment in an ice-influenced and megatidal (~14 m tidal amplitude) region. •Restoration stages identified for salt marshes in mega-tidal, high-energy environments.•Deposition of unconsolidated sediment immediately after breaching dikes can be very high.•Ecosystem engineer Spartina alterniflora can spread vegetatively or via seedlings.•Faunal communities require established vegetation (S. alterniflora, algae/ditch grass).•Old dikes provide essential protection for developing salt marshes.