Improved benthic fauna community parameters after large-scale eelgrass (Zostera marina) restoration in Horsens Fjord, Denmark

Eutrophication is a key driver in the loss of marine ecosystems, and seagrass meadows are among the many ecosystems which have declined globally during the last decades. Seagrass restoration is being used worldwide in coastal areas to counteract the decline in areal extent and to promote biodiversity. This study assesses the spatial and temporal changes in benthic fauna composition after a successful large-scale eelgrass (Zostera marina) transplantation in Horsens Fjord, Denmark. Transplantation was done by anchoring individual shoots in the sediment. Subsequently, benthic fauna was compared among bare bottom (BB), transplanted eelgrass (TE) and a natural eelgrass (NE) meadow in Horsens Fjord. Species richness (S), abundance (N), Shannon-Wiener index (H’), Pielou’s evenness (J’) and biomass (B) of benthic fauna were significantly higher at TE and NE than at BB. S, H’ and J’ were not different between TE and NE, but N and B were. Furthermore, S, N and B showed significant year-to-year variation, with the highest values occurring the same year as peak eelgrass biomass at both TE and NE, and S, N and H’ correlated positively with dry eelgrass biomass. Increases in community parameters were achieved at TE at least 1 yr 2 mo after transplantation, and a higher diversity of feeding groups was found. However, the ecological status of fauna at TE was in a transition state towards that at NE, according to the Water Framework Directive. The fast succession of benthic fauna proved that successful large-scale transplantation of eelgrass can restore fauna communities very quickly.