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

International audienceAn 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

Four-Year Temporal Study of an Intertidal Artificial Structure in the English Channel

An experimental artificial structure was deployed in March 2014 on the intertidal zone of the Bay of Seine (eastern part of the English Channel), at intervals of one year until April 2018, i.e., from February 2015 onwards, two blocks were collected in April each year. This study provides an inventory of sessile and motile invertebrates living on the artificial hard-bottom and describes the stages of colonization and succession during the four-year study. A total of 84 taxa were identified including 13 sessile and 71 motile taxa. For the sessile fauna, only two taxa Balanus crenatus and Mytilus edulis had colonised the blocks in 2014, and the Taxonomic Richness (TR) was relatively stable during the next three years (between 8 and 10 taxa). The TR of the motile fauna showed an increase between 2014 (5 taxa) and 2015 (34 taxa), and then decreased from 54 taxa in 2017 to 29 taxa in 2018. The abundance of the sessile fauna was very high in 2014 due to the rapid settlement of the barnacle Balanus crenatus, which remained the dominant species throughout the study. Another barnacle Perforatus perforatus, the blue mussel Mytilus edulis and three ascidians including two non-indigenous species Perophora japonica and Corella eumyota, and Molgula sp. were also among the dominant taxa of the sessile fauna. In April 2014, the dominant motile taxa was the decapod Carcinus maenas juvenile, then in 2015 the fauna became dominated by pioneer taxa such as the amphipod of the genus Monocorophium and the tanaid Zeuxo holdichi. A reduction of mean abundance was observed in the last three years of the study, combined with diversification of the dominant species especially those of small size such as Peracarida. The study shows that the colonization of such blocks deployed on oyster tables in the intertidal zone is efficient to test the ability of building material to be colonized in this transition zone

Colonisation of artificial structures by primary producers: competition and photosynthetic behaviour

International audienceColonisation of artificial structures by primary producers is an important determinant for eco-engineering projects. In this context, interactions between the colonisation by microphytobenthic biofilm and macroalgae were explored on 48 samples of marine infrastructures (MI) immersed for one year in the English Channel. Marine infrastructures samples with smooth and rough surface were compared to evaluate the influence of surface micro-scale rugosity. Microphytobenthos biomass (MPB), macroalgal diversity and photosynthetic parameters of both were assessed during colonisation. No significant differences were found as a function of the surface rugosity of MI samples, which was unexpected, but can be explained by biogenic rugosity provided by barnacles. Marine infrastructures were largely colonised by a red encrusting alga, Phymatolithon purpureum, which showed poor photosynthetic capacity compared to the microphytobenthos present next to it. Colonisation by monospecific encrusting algae tended to reduce the primary productivity of hard substrate