Fig. 2

Shannon-Wiener index (H′) and Simpson index (D) of biodiversity for all cruises, based on the list of species defined as quantitatively relevant. The graphs show the deviation from the mean (H′ = 2.12, D = 0.19). For congruence of the indices means, the right y-axis was inverted and the means for both indices were matched to each other. The solid (grey and black) lines depict the linear trends of both indices. No data are available for the years 1998, 2000 and 2007