Benthic habitat quality assessment of an oxygen stressed fjord by surface and sediment profile images

In May and October 1994 the benthic habitats in Havstensfjord (26 km2), a seasonally oxygen stressed stratified fjord, were classified by taking sediment surface and sediment profile images (SPI) at 90 stations, randomized into nine strata. Qualitative grab samples for faunal inspection were taken at about of the stations in both May and October to help to identify objects in the images. The images give information on sediment characteristics (texture, oxic/anoxic conditions, lamination) which often can be related to functional properties of the macrofauna (burrows, tubes, feeding voids, reworked sediment) or to observations on benthic epifauna. In combination, such variables mirror the quality of the benthic habitat. Analysis of sediment profile images was done with multivariate methods [Benthic Habitat Quality (BHQ) index] and univariate statistical methods to describe differences between areas and depths. Variance analysis of BHQ indices indicated a significant interaction between area and depth. In both the northeast and northwest strata the oxygen stress had induced a habitat degradation at depths deeper than 25 m compared to shallower northwest and northeast strata and all south depth strata. No significant difference in mean BHQ index was found between May and October. We discuss the potential application of the SPI technique for efficient monitoring oxygen stressed marine coastal areas.