Characterization of soft-bottom benthic habitats of the Aland Islands,northern Baltic Sea

Abstract

Sediment surface and profile imaging (SPI) was used in combination withgrab sampling of sediment (sediment type, organic content, benthic infauna)and hydrography (temperature, oxygen saturation of bottom water) to analyzeand describe the soft-bottom benthic habitats of the Aland archipelago (60°00' to 60° 30' N, 19° 30' to 20° 30' E) in the northern Baltic Sea. TheSPI analysis covered 42 stations (5 to 263 m depth), from inner shelteredbays to open coastal waters, with varying sediment types (soft mud with highorganic content to sandy substrates with low organic content; loss onignition: 0.5 to 12.4%). Clustering of the sampled stations (sedimentproperties) yielded 3 distinct categories of sedimentary habitats: (1) innerarchipelago areas and bays with high organic content of the sediment andreduced oxygen saturation in the bottom water, (2) archipelago waters withintermediate values of all analyzed parameters, and (3) open coastalsediments with low organic content and high oxygen saturation (2 deepoffshore stations formed an additional group based primarily on depth).Visual analysis of the images provided information on several additionalabiotic and biotic characteristics of the sediment, and significantcorrelations were found mainly between oxygen saturation, organic content,sediment type, shear strength (penetration of gear), surface relief and thedepth of the redox potential discontinuity layer in the sediment. Thesediment properties were also reflected in the zoobenthos. The correlationsbetween parameters measured are discussed in relation to applicability of theSPI method, monitoring demands, and basic understanding of the sediment-animal relationships.