Marine Amphipoda and environmental occurrence around Iceland

The distribution and diversity of amphipod crustaceans of Icelandic waters, in water depths between 18-3700 m, was examined and how it relates to environmental parameters and depth. Data on amphipod occurrence and abundance were collated from the historical literature (Ingolf Expedition, 1895-96), as well as recent expeditions (1998-2018) such as BioIce (Benthic invertebrates of Icelandic waters) and IceAge (Icelandic marine Animals: Genetics and Ecology, www.iceage-project.org) resulting in 355 amphipod species amongst 71,108 individuals from 532 localities. Samples were taken by a number of trawled sampling devices, including different types of dredges and sledges, as well as Remotely Operated Vehicle (ROV). A 1 ° hexagonal grid was constructed in to map the distribution of the amphipod species alongside twelve environmental factors retrieved from the Bio-Oracle 2.1 database. Due to strong autocorrelation of some of these factors, the analysis was limited to a set of eight variables: depth, pH, phytobiomass, velocity, dissolved oxygen, dissolved iron, salinity, and seabed temperature. Based on these faunistic and environmental data, four biogeographical clusters could be identified: a coastal cluster, a species cluster along the borders of the Greenland-Iceland-Faroe Ridge (GIFR), which separates the deep-sea basins north and south of Iceland, a cluster that is limited to the deep sea to the north of the GIFR, and one that is restricted to the deep-sea south of the GIFR. Diversity as measured by Hill numbers differed considerably between these clusters, with the diversity of the shallow cluster (Coastal and GIFR) to be higher compared to the two deep-sea cluster (Deep North and Deep South). Analysing diversity across a depth gradient, diversity showed a hump-shaped curve with diversity peaking at upper slope (500 m) depth. Depth, salinity and temperature of the seabed were identified as the main parameters to shape the distribution of amphipods around Iceland. Perceived diversity and distribution patterns were discussed with regard to the influence of historical (e.g. oceanography, climatic conditions) and contemporary environmental factors.