Retreating coastal forest supports saltmarsh invertebrates

Abstract

AbstractAs sea‐level rise converts coastal forest to salt marsh, marsh arthropods may migrate inland; however, the resulting changes in arthropod communities, including the stage of forest retreat that first supports saltmarsh species, remain unknown. Furthermore, the ghost forest that forms in the wake of rapid forest retreat offers an unknown quality of habitat to marsh arthropods. In a migrating marsh in Virginia, USA, ground‐dwelling arthropod communities were assessed across the forest‐to‐marsh gradient, and functional use of ghost forest and high marsh habitats was evaluated to determine whether marsh arthropods utilized expanded marsh in the same way as existing marsh. Diet and body condition were compared for two marsh species found in both high marsh and ghost forest (the detritivore amphipod, Orchestia grillus, and the hunting spider, Pardosa littoralis). Community composition differed among zones along the gradient, driven largely by retreating forest taxa (e.g., Collembola), marsh taxa migrating into the forest (e.g., O. grillus), and unique taxa (e.g., Hydrophilinae beetles) at the ecotone. The low forest was the most inland zone to accommodate the saltmarsh species O. grillus, suggesting that inland migration of certain saltmarsh arthropods may co‐occur with early saltmarsh plant migration and precede complete tree canopy die‐off. Functionally, O. grillus occupied a larger trophic niche in the ghost forest than the high marsh, likely by consuming both marsh and terrestrial material. Despite this, both observed marsh species primarily consumed from the marsh grass food web in both habitats, and no lasting differences in body condition were observed. For the species and functional traits assessed, the ghost forest and high marsh did not show major differences at this site. Forest retreat and marsh migration may thus provide an important opportunity for generalist saltmarsh arthropods to maintain their habitat extent in the face of marsh loss due to sea‐level rise.