Abstract: Arctic Ocean sea ice coverage reached a record minimum of 3.41 million km2 in 2012. Zooplankton samples collected from 22 stations during summer 2012 were analyzed to determine the composition and geographic distribution of various Arctic Ocean communities, and to identify relationships to environmental conditions. Three geographically distinct communities were identified. The southern Chukchi Sea (CS) community was dominated by barnacle larvae (total abundance 56.6%–79.8%), followed by copepods (18.0%–42.2%). The central and northern CS community was dominated by copepods (62.3%–96.8%) followed by barnacle larvae (0%–30.9%). The deep-sea community was dominated by copepods (71.6%–89.8%) and characterized by extremely low abundance. The zooplankton community at Station M06, located at the edge of the CS slope, could not be classified into one of the three communities. Abundance was similar to CS communities but composition was similar to deep-sea communities. Calanus glacialis, Pseudocalanus sp., Oikopleura vanhoffeni, and barnacle larvae were dominant in the two shallow water communities. There were more dominant species in the deep-sea community, mostly large copepods including Calanus glacialis, Calanus hyperboreus, and Metridia longa. Surface temperature and salinity were the most important environmental factors determining the geographical distribution of communities. There was no significant change in community patterns and geographic distribution compared to 2003 results (when sea ice coverage was higher), but total abundance of zooplankton in the CS increased up to 2-fold and total abundance decreased in the deep-sea community with an increase in the percentage of large copepods.

Key words: Chukchi Sea, zooplankton, community pattern, community structure, dominant species, copepods, barnacle larva