Effects of material composition and face block exposure on the long-term (2014-2018) colonisation of an intertidal RECIF Artificial Reef in the Bay of Seine

Abstract

An experimental artificial reef (AR) with the incorporation of crushed seashells of the queen scallop Aequipecten opercularis was initiated on the intertidal zone of the Bay of Seine in the framework of the INTERREG IVa RECIF project for a everyone year monitoring observations from March 2014 to April 2018. Three block types were operated: eco-friendly material with 20% or 40% of crushed queen scallop shells, and ordinary concrete made from natural aggregates. On the seven blocks analysed at the end of the experiment in 2018, 74 taxa including 32 sessile and 42 motile fauna have been accounted; no difference of taxonomic richness was observed between material and immersion time. The sessile fauna was identified for the six external faces of two blocks aged of four years: horizontal above face (FAB), horizontal below Face (FBE), face oriented offshore (FOF), face oriented inshore (FIN), vertical face oriented west (FEW) and vertical face oriented east (FEA). FBE showed higher taxonomic richness and abundance than the other block faces. FAB exposed to the light showed the lowest abundances. Our observations showed the efficiency of such AR on the intertidal zone accessible at each spring tide, which was easier to survey than in the subtidal zone, where divers must be mobilised to sample blocks.