Subtidal macrobenthos monitoring in function of a foreshore suppletion at the Belgian coast, period 2013-2016

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What ecological effects does a foreshore suppletion, and a beach suppletion, have on the marine ecosystem in the intertidal and shallow surf zone (<6 m depth)? The foreshore suppletion (400.000m³) was by means of an experimental set-up in the shallow coastal zone (-1 to -2m TAW) of Mariakerke. Beside it, a beach nourishment was conducted at Mariakerke (681243m³) and Middelkerke (968754m³). For the Mariakerke area, we collect biological and sedimentological samples in the impact area and in a control area (Bredene), before as after the suppletion, whereas for Middelkerke only the data after suppletion was part of the study. We monitor the marine ecosystem with a focus on the fauna within the sediment (macrofauna) and on the sediment (hyperbenthos, epi- and demersal fish fauna) in the intertidal zone and subtidal zone. In both studies, the subtidal area is the zone between the low water line and the 6m depth line and the intertdial area is the zone between low and high tide water line.

This dataset contain the macrobenthic data collected in the subtidal area. Macrobenthos are the biota that lives in the sediment and are retained on a sieve of 1mm. The sampling design for the monitoring is following the BACI-design (Before After Control Impact), with a control area with similar habitat characteristics outside the influence of the suppletion activity. There is sampled before the suppletion and in the following two years after suppletion. In this BACI-monitoring, the seasonal aspect is taken into account, by taking samples in spring (March) and autumn (September). In the subtidal area, three depth strata were determined to investigated the influence of the suppletion outside the suppletion area. Stratum a (between low water line and -2m TAW) is the area were the foreshore suppletion is executed. Stratum b and c are taken respectively the depth zones -3m to -4m and -5m to -6m TAW. The amount of sampling locations was determined by the client and determines 15 points for each sampling moment. That amount of samples was via a systematic random stratified strategy distributed over each stratum (5 in each strata). The samples were taken with a Van Veen grab (0.1m²). The samples were sieved alive on a 1mm sieve and then fixed with an 8% formaldehyde-seawater solution. The sieved material is stained with eosin. All biota were determined and counted to species level following a standardized taxonomic discrimination protocol. This to determine the determination level and if certain life stages (larvae, juveniles) need to be discriminated. The biomass is determined as wet weight. All macrobenthic samples were taken following the ISO16665:2005(E)) (“Water quality – Guidelines for quantitative sampling and sample processing of marine soft-bottom macrofauna”). Moreover, the analyses (identification, counts and biomass) were conform NBN EN ISO/IEC 17025 standard executed (cfr. BELAC nr. 315-TEST: date 28/04/2016, valid until 05/03/2020).

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