H. Fock ® F. Uiblein ® F. Ko¨ ster ® H. von Westernhagen Biodiversity and species–environment relationships of the demersal fish assemblage at the Great Meteor Seamount (subtropical NE Atlantic), sampled by different trawls Received: 11 October 2001 /Accepted: 28 January 2002 / Published online: 12 April 2002 Ó Springer-Verlag 2002 Abstract Quantitative data collected with different bot- tom trawls at the Great Meteor Seamount (subtropical NE Atlantic, 30°N; 28.5°W) in 1967, 1970 and 1998 are compared. Bootstrap estimates of total catch per unit effort increased from 6.96 and 10.8 ind. m –1 h –1 in 1967 and 1970, respectively, to 583.98 ind. m –1 h –1 in 1998. Gear effects and an effect of gear over time accounted for 47.1% and 20% of species variability. Further sig- nificant factors were time of day and habitat, while season was not significant. A total of 43 species was collected. Including supplementary species information, agrandtotalof46specieswasfoundassociatedwiththe Great Meteor Seamount. Diversity was higher in 1967 and 1970 (Shannon’s diversity: H¢=2.5 and 1.6) than in 1998 (H¢=0.9). Species–environment relationships are discussed in terms of a sound-scattering layer–intercep- tion hypothesis, i.e. utilisation of prey from a diurnally moving sound-scattering layer for the bentho-pelagic community. This is probably augmented by concentra- tion effects in a circular current around the seamount (Taylor-column). Long-term changes are discussed with respect to a decrease in biodiversity due to considerable increases in Macroramphosus scolopax and Capros aper. In 1998, the increase of abundance of Trachurus pictu- ratus and the respective decreases for genuine benthic species were likely to have been caused by a change of gear. Introduction TheGreatMeteorSeamount(GMR;30°N;28.5°W)isa large, isolated, flat-topped seamount in the central eastern Atlantic (Pratt 1963). It covers an area of 1,465 km 2 , with a minimum depth of 275 m (Fig. 1A). All data on the GMR gathered prior to 1945 were lost (Pratt1963).Sincethen,firstecologicalinvestigationson GMR were carried out in 1967 and continued in 1970 (e.g. Hesthagen 1970; Kotthaus 1972; Weikert 1972; Nellen 1973; Weigmann 1974). Demersal fishes were investigated quantitatively by Ehrich (1977) and quali- tativelybyMaul(1976).Pelagicstockswereinvestigated by Kotthaus (1972). Recently, data on primary pro- duction and hydrography have further supplemented existing knowledge (Mourino et al. 2001). The status of fisheries at GMR is unknown; however, it has at least been subject to exploratory fishing (e.g. Shcherbachev et al. 1985). GMR is assigned to the biogeochemical province of the Subtropical Eastern Gyre (Sathyendranath et al. 1995). In this oligotrophic province, primary production estimates are comparably low, ranging from 88 and 140gCm –2 year –1 (afterYentsch1990;Plattetal.1995; Sathyendranathetal.1995).Theadjacentdomaintothe north, the North Atlantic Drift, has a higher annual production of approximately 170–240 g C m –2 year –1 . For the North Atlantic Tropical Gyre to the south, production is slightly lower (approx. 80–120 g C m –2 year –1 ). The seasonal cycle is weak, and the water col- umn is almost permanently stratified (Jickells et al. 1996). Chlorophyll distributions are characterised by a winter maximum and summer minima (Campbell and Aarup 1992; Mourino et al. 2001). Despite impoverished nutritional conditions in the ambient oceanic regions, seamounts often maintain high Marine Biology (2002) 141: 185–199 DOI 10.1007/s00227-002-0804-y Communicated by O. Kinne, Oldendorf/Luhe H. Fock (&) ® H. von Westernhagen Alfred-Wegener-Institut fu¨r Polar- und Meeresforschung, Am Handelshafen 12, 27515 Bremerhaven, Germany E-mail: hfock@awi-bremerhaven.de Tel.: +49-471-48311382 Fax: +49-471-48311425 F. Uiblein Institut fu¨r Zoologie der Universita¨t Salzburg, Hellbrunnstr. 34, 5020 Salzburg, Austria F. Ko¨ster Institut fu¨r Meereskunde der Universita¨t Kiel, Du¨sternbrooker Weg 20, 24105 Kiel, Germany