Do foraminifera mirror diversity and distribution patterns of macrobenthic fauna in an Arctic glacial fjord?

• We compared responses of Foraminifera and macrofauna to glacial impacts.
• Patterns of species distribution in two groups in a glacial fjord were correlated.
• Species richness and density of both groups declined towards glaciers.
• Foraminifera can be a useful indicator of other benthic groups variability.

This paper compares the distribution and diversity patterns of benthic foraminifera (all taxa and only calcareous forms) and macrozoobenthos in an Arctic glacial fjord. The samples were collected at 22 stations located in Hornsund (west Spitsbergen). The activity of tidal glaciers located in the inner basins causes steep environmental gradients of turbidity, organic matter supply, and sediment stability. Clear differences in density, diversity and species composition were documented for both foraminifera and macrofauna between the groups of stations located in three zones along a gradient of increasing tidal glacier impact. The assemblages of both benthic compartments in the glacial bay were dominated by small, opportunistic, infaunal species (i.e., Cassidulina reinforme for foraminifera and cirratulid polychaetes for macrofauna) which occurred throughout the fjord, but showed an increase in density and/or dominance when approaching the glaciers. A parallel decreasing pattern from the central basin to the inner glacial bay was noted with regard to species richness and faunal density of both groups. Macrofaunal evenness decreased close to glaciers, but this was not observed in the foraminiferal assemblages. The distribution patterns of calcareous foraminifera were correlated (p = 0.001) both with those of all foraminifera (agglutinated and calcareous taxa) and with macrofauna, with the Spearman's rank correlation between the respective Bray Curtis similarity matrices ranging from 0.94 to 0.99 (total foraminifera), and from 0.37 to 0.67 (macrofauna), respectively. Species richness, expressed as the number of species per sample, and diversity, expressed by the Shannon–Wienner index, of foraminifera and macrofauna were also significantly correlated (Pearson correlation r = 0.79, r2 = 0.62, p < 0.0001 for species richness, Spearman correlation rho = 0.96, p < 0.05 for diversity). Our study provides evidence that the patterns of calcareous foraminifera density, diversity and species composition in a glacial fjord can be effective, reliable indicators of variability of these characteristics in other benthic compartments.