Development of the benthic macrofauna community after tidal restoration at Rammegors

The managed realignment project Rammegors aims at re-establishing estuarine nature in a formerly freshwater wetland. For this purpose, a tidal inlet was constructed in the Krabbekreekdam to generate a reduced tidal influence that should allow the development of salt marsh area, tidal flat area and low energetic shallow sub-tidal. A central question of the Rammegors tidal restoration project is how the flora and fauna will develop in the area. To understand the biotic and abiotic processes related to the tidal restoration in Rammegors, a monitoring programme is being executed by the Centre of Expertise Delta Technology. The monitoring focuses on the main biotic and abiotic developments in the area. This progress report only focuses on the early colonization of macrobenthic invertebrates in Rammegors. Benthic macrofauna and sediment sampling took place in spring and autumn 2017 at twenty stations along 4 transects with varying distances to the outlet. A fast colonization of the benthic macrofauna was observed in Rammegors. Twenty and twenty-eight taxa were observed in the area in spring and autumn 2017 respectively. The communities significantly differed between spring and autumn. In spring densities reached high values, especially for the brackish mud shrimp Manocorophium insidiosum and mosquito larvae Chironomidae. In autumn these brackish species almost disappeared from the area. Their presence in autumn, even in low numbers, as well as the observation of the brackish cockle Cerastoderma glaucum indicate that, after the tidal restoration, parts of Rammegors are still under influence of brackish water. A relation was found between elevation and the benthic macrofauna development. Species richness showed an optimum around +0.4m NAP with lower values at both lower and higher elevations. Total density significantly increased with elevation, with highest total density at the higher elevations and a gradient in ecological richness was observed with higher richness further from the inlet. As the spring community significantly differs from the autumn community, we will continue sampling in both seasons in 2018