Abstract
Anthropogenic activities such as sand extraction, fisheries, shipping, the construction of pipelines or windmill farms, dredging and dumping of dredged material, have been shown to result in varying effects on the marine ecosystem (Köller et al. 2006, Wilhelmsson et al. 2006, Barrio Froján et al. 2008, La Porta et al. 2009, Ware et al. 2009). Numerous monitoring programs have been set up to evaluate the extent and nature of these effects. However, the effects of anthropogenic activities on the benthic life are often difficult to detect against a background of small and large scale natural variability resulting from differences in environmental variables, especially in the highly dynamic sandbank-dominated habitats in the Belgian Part of the North Sea (BPNS).
The distribution of the macrobenthos in the BPNS is well studied, and four major species assemblages were defined (Van Hoey et al. 2004, Degraer et al. 2008). Each of these assemblages is determined by a number of indicator species and by typical density and diversity measures. The distributional patterns of the macrobenthic assemblages are mainly linked to sediment type (cf. average grain size and mud content). Based on that relation, a habitat suitability map for the four assemblages could be established for the BNPS (Degraer et al. 2009).
On the other hand, distributional patterns of the epibenthos and demersal fish in the BPNS are not yet thoroughly presented. In the framework of an ecosystem approach, knowledge on epibenthos and demersal fish communities, in addition to macrobenthos data, is imperative, and will allow for sound ecosystem-based management. Furthermore, knowledge on the natural variability of these communities will underpin a sound interpretation of the detection of any ecological change in the area.
A monitoring strategy based on medium-term data acquisition at fixed locations is used to define demersal fish and epibenthos communities and to evaluate their natural spatial and temporal variability in the BPNS. In total, 80 locations spread over the BPNS were sampled with an 8 m shrimp trawl during 1 to 9 (spring and autumn) campaigns between 2004 and 2009. Five tracks are located in sand extraction areas, five in dredge dumping sites and two in windmill areas, and could thus be defined as impact locations, while 68 tracks are regarded as reference locations. A number of environmental variables were used in the analysis of the spatial distribution of the encountered species.