Abundance, composition, and development of zooplankton in the Subarctic Iceland Sea in 2006, 2007, and 2008

A large-scale study of zooplankton from surface waters and depth-stratified sampling at selected sites in the Iceland Sea was conducted during the years 2006–2008. The abundance of mesozooplankton was low during winter, when animals were mostly confined to the colder (∼0°C) and deeper (∼200–1000 m) layers, and peaked during late summer (∼11–18 g dry weight m−2, ∼300 000–400 000 ind. m−2), when animals resided mainly above the 50–100-m depth range. Diversity was greatest near the shelf edges and least in the central Iceland Sea. Around 32% of mesozooplankton variability was explained by six variables [longitude, year 2008, temperature, bottom depth, chlorophyll a (Chl a), and salinity]. Three main mesozooplankton communities were identified: (i) an Atlantic community in the east, with Calanus finmarchicus and Pseudocalanus spp. most abundant, (ii) an Arctic community at high latitudes, with large numbers of C. hyperboreus and C. glacialis, and (iii) a community with coastal affinities at lower latitudes, with large numbers of Temora longicornis and Acartia spp. Longitude and Chl a explained ∼43% of macrozooplankton variability (euphausiids and amphipods). Results show that the region is a meeting place of Arctic and Atlantic species, with the copepods C. finmarchicus and C. hyperboreus, the amphipod Themisto abyssorum, and the euphausiid Thysanoessa longicaudata the key players.