A human driver of change in the southern Baltic coastal sedimentary system: monitoring effects of dredging spoil dumping on benthic communities

Construction of coastal infrastructure, e.g. seaward port facilities, frequently calls for sediment removal (dredging). Deposition of the dredging spoil at designated offshore sites (dumping grounds) disturbs the dumping ground sedimentary system, including the biota. Assessment of environmental effects of dumping requires monitoring of the system’s responses to the disturbance severity and persistence. In 2011-2017, we followed changes in sediment characteristics and descriptors of benthic (meio- and macrofaunal) assemblages (abundance, biomass, composition) in a shallow southern Baltic coastal area serving as a dumping site for dredging waste from a new harbour under construction at the coast. At the initial phase of the disturbance, the benthos responded rapidly (abundance and biomass reduction, altered composition), and equally rapidly recovered when dumping was temporarily suspended. After the dumping operations were resumed, the responses intensified, although apparent colonizers (benthic copepods in the meiobenthos and juvenile molluscs in the macrobenthos) tended to appear intermittently in the disturbed areas. The benthos remained impoverished in the altered habitat after dumping was terminated, reflecting the severity of habitat change.