THE BENTHIC COMMUNITIES OF THE SNORRE FIELD IN THE NORTHERN NORTH-SEA(61-DEGREES-30' N 2-DEGREES-10' E) .1. THE DISTRIBUTION AND STRUCTUREOF COMMUNITIES IN UNDISTURBED SEDIMENTS

The fauna of the Snorre oil field is diverse and varies along a 40 m d epth gradient across the area. Abundance and species richness increase with increasing depth but diversity is highest in the centre of the g radient. The communities present differ widely from those of the adjac ent but shallower Statfjord, Gullfaks and Tordis Fields and from the m ajor communities found throughout much of the northern North Sea, a fa ct attributable to the greater depth, finer sediments, higher sediment organic levels and position on the western slope of the Norwegian Tre nch. They have greater affinities with the communities in the Troll Fi eld, 85 km SE on silt/clay sediments in the floor of the trench and th e Heidrun Field, situated approximately 390 km N at similar depths and in an area of similar sedimentary composition. However the Snorre com munities have a much higher number of suspension feeding and surface d eposit feeding organisms than either of these other areas. This might be caused by higher current speeds in the Snorre area which could crea te favourable conditions for suspensivores. Such water movements might bring occasional incursions of intermediate Norwegian Sea water into the area. Indeed the Snorre fauna appears to bear some relationships t o the intermediate depth faunas of the Norwegian Sea, and is clearly d ifferent from most of the better described northern North Sea faunas.