Characterization of soft-bottom benthic habitats of the Aland islands, northern Baltic sea

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