Depth correlated benthic faunal quantity and infaunal burrow structures onthe slopes of a marine depression

In the northern part of the Kattegat, western Sweden, a series of marine de pressions remain since the last glaciation. One of these, the well-oxygenat ed Alkor Deep, is about 3 km long and 800 m wide and with a depth of 138 m. Random depth-stratified sampling was made along four transects on the slop es including benthic macrofauna (0.1 m(2) grab samples) and sediment profil e imaging. A significant positive correlation was found between depth and t he faunal variables abundance and biomass. Deposit feeders such as Maldane sarsi, Heterormastus filiformis and Abra alba were among the dominants and may have been supported by down-slope advected organic material. In many im ages, pockets and extensive burrows were seen in the sediment that appeared to be constructed by the crustaceans Calocaris macandreae and Maera loveni . The ecological significance of their irrigation of the sediment is discus sed. Due to the faunal activity deep down in the sediments of the slopes, t he mean apparent redox potential discontinuity (RPD) was found as deep as b etween 8.0 and 11.3 cm depth, and RPD was significantly positively correlat ed with water depth. On the slopes there appears to be a balance between th e input of organic material and the capacity of the benthic organisms to as similate that carbon. (C) 2000 Academic Press.