Diel and habitat-dependent resource utilisation by deep-sea fishes at the Great Meteor seamount: niche overlap and support for the sound scattering layer interception hypothesis

Interspecific relationships of 4 dominant fish species of the Great Meteor seamount fish community (subtropical NE Atlantic, 30degreesN, 28.5degreesW), Macroramphosus spp. Lacepede 1803, Capros aper (L. 1758), Antigonia capros Lowe 1843 and Zenopsis conchifer (Lowe 1852) were analysed with respect to diet composition, habitat-dependent resource utilisation and niche overlap. For all 4 species, planktonic and micronektonic prey prevailed. In terms of the Relative Importance index (RI), the benthic share was 18.25 % RI for Macroramphosus spp., 19 % RI for C. aper and 20.38 % RI for A. capros. Prey of Z. conchifer consisted of 48.57 % RI mesopelagic and pelagic fishes and of 47.7 % RI bentho-pelagic fishes. For all fishes, a permutation test revealed significant selection of prey in plateau margins of the seamount. Unweighted and novel-weighted overlap indices combining prey composition, habitat use and prey utilisation within habitats revealed high overlap between the boarfishes A. capros and C. aper and smaller overlap between other pairs. The results are in support of the sound scattering layer interception hypothesis (Isaacs & Schwartzlose 1965), which implies: (1) primarily pelagic food utilisation for bentho-pelagic fishes; (2) increased habitat-dependent utilisation rates at locations of interception with the sound-scattering layer; (3) diel changes in utilisation rates due to availability of prey; (4) sufficient resource partitioning among species in order to avoid competitive exclusion.