On the structure of the neritic suprabenthic communities from the Portuguese continental margin

Abstract

Thls work presents the investigations made on the n e r ~t ~c suprabenthlc communities of the Portuguese margln (continental shelf and upper slope) exposed to seasonal upwelllng These communitles were sampled dunng the AVEIRO-94 crulse at 5 sites located along an E-W bathymetnc transect from 21 to 299 m depth using a suprabenthlc sled with s u p e ~p o s e d nets In the 0 to 100 cm water layer the total denslties ranged from 700 2 to 13591 7 lnd lOOm During daytime the motile fauna was m a ~n l y concentrated within the 0 to 50 cm water layer (76 2 to 97 2 % of the total abundance) The night-time sample at the shallower site showed a more even d~stnbution of the fauna in the nearbottom water layers (nocturnal migratory behaviour of some motile species) The Shannon diversity (H') values ranged from 1 8 4 to 3 54 for the shelf sites and increased at the upper slope site (4 15) Mysids and amphipods were generally dominant except for at the middle part of the shelf where the latter was replaced by euphausuds The suprabenth~c fauna off Aveiro was compared with slmilar data from the same bathymetnc samphng levels off Arcachon (Bay of Biscay) Multivanate analysis showed that differences in faunal composition between the 2 geographic areas were smaller than depth-related vanahons within geographic areas The results were discussed in relation to other suprabenth~c communities from the northeastern Atlantic KEY WORDS Suprabenthos .