Submarine hard-bottom substrates in the western Baltic Sea – human impact versus natural development

Schwarzer, K., Bohling, B., Heinrich, C., 2014. Submarine hard-bottom substrates in the western Baltic Sea–human impact versus natural development. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium(Durban, South Africa),Journal of Coastal Research, Special Issue No. 70, pp. 145–150, ISSN 0749-0208. Large areas of the seafloor in the western Baltic Sea are covered by lag deposits of Pleistocene origin, consisting of gravel, stones and boulders. From about 1800–1974, commercial extraction of stones and boulders from these shallow submarine areas was carried out. These activities have fundamentally changed the sediment distribution patterns and ecological conditions of the seafloor. Based on comparisons between old analogue and modern digital sidescan sonar images and direct abrasion measurements on the seafloor by scuba divers, the development of this hard-bottom substrate was studied on a decadal to seasonal scale. We show that due to abrasion processes the amount of boulders has been increased over a 22 year period. Thus, natural regeneration of hard-bottom substrate and improvement of the ecological status of the shallow marine environment is possible. This needs to be considered in order to reestablish a “good ecological status” as demanded by administrative guidelines like the EU Water Framework Directive and the Marine Strategy Framework Directive.