The pelagic invertebrate community includes a wide variety of other species, including amphipods, mysids, shrimp, squid, jellyfish, pteropods, chaetognaths, and ichthyoplankton.  There are only two Arctic species of pelagic shrimp and they do not appear to be a common component of the nekton (Hopcroft et al. 2008).  This section will focus on certain elements of the pelagic invertebrate community that are important food web components.

Krill

Unlike the Antarctic, euphausiids are not abundant in Arctic waters.  However they can be difficult to accurately assess in ice-covered waters as they seek shelter in the pockets and fissures in the ice (Percy and Fife 1985).  Euphausiids are not considered to be a truly Arctic species, rather they are advected from the Bering Sea Water inflow (Suydam and Moore 2004) or from the Atlantic (Letessier et al. 2009).    The euphausiids Thysanoessa raschii and T. inermis were important prey items associated with bowhead whales in the western Beaufort Sea (Brinton 1962).  Euphausiids are found from the surface to the deep midwater pelagic areas, in depths greater than 500 m. 

Amphipods

Free-swimming amphipods are a key component of the Arctic food web, representing a link between zooplankton and higher level consumers such as fish, marine mammals, and birds.  Hyperiid and Lysianassid amphipods are among the common taxa found in Arctic waters and are a dominant component of the zooplankton abundance and biomass (Auel et al. 2002).  The hyperiid amphipod, Themisto libellula is a pan-Arctic species that can occur in high numbers in the ice free waters of the Arctic.  Based on the high amounts of C20:1 (n-9) and C22:1 (n-11) fatty acids and alcohols found in T. libellulatissues, their diet was domianted by Calanoid copepods.  Further analysis indicated a close association with ice-algal production.  This confirms field sampling data showing Themisto sp. associated wtih sympagic communities.

Themisto abyssorum is more closely associated with deepwater communties.  Themisto abyssorum is  considered to be a boreal species and is found in close association with the Atlantic Water that moves northward through Fram Strait.  Abundance generally decreases from east to west, dropping from >200 ind/m² over the contiental slope north of Spitsbergen to <40 ind/m² in the central Arctic (Auel et al. 2002).  It does not show a similar lipid signature seen in T. libellula, indicating that copepods are not a dominnant component of the diet.  Rather, the deepwater species is more likely an omnivore and scavenger.

Cyclocaris guilelmi, is also an epipelagic species, occurring in the deep-waters of the Arctic.  As wtih T. abyssorum, C. guilelmi appears to be Atlantic in origin but is found throughout the Arctic ocean.  Kraft (2012) found C. guilelmi to be a dominant component found in deepwater traps in Fram Strait.  The population appeared to be stable with peaks from August to February.

Cephalopods

Cephalopods are a predator of and a key prey item for many of the VECs in the Arctic.  Squid move vertically through the water column, integrating marine resources throughout the pelagic environment.  The squid Gonatus fabricii is the most commonly reported species in the Arctic, with numerous records in the Atlantic sector, the Barents Sea and the high Canadian Arctic (Gardiner and Dick 2010). Berrytheuthis magister is the predominant squid species found in the Pacific domain.  Squid exhibit all manners of vertical distribution: near-surface dwellers (to 50 m), vertical migrators that either move into the surface waters at night or just move higher in the water column, and near-bottom dwellers.  In addition, some species exhibit ontogenetic descent moving progressively deeper as they age (Roper and Young 1975).  Cephalopods are voracious predators feeding on crustaceans, fish, other squids, and zooplankton.  Based on isotope analysis, squid are occupying different trophic levels in different regions (Navarro et al. 2013) indicating that squid are able to shift their diet based on availability.  The isotope ratios for Arctic squid indicated a trophic level of 3 to 5.  Squid are an important component of marine mammal and sea bird diets, including narwhals, White whales, walrus, murres and fulmars (Gardiner and Dick 2010).

Jellyfish

Gelatinous zooplankton are poorly understood in the Arctic, largely due to the difficulty of capturing them with traditional sampling methods.  However, they are considered to be a substantial sink for primary and secondary production (Purcell et al. 2009).  In the Beaufort Sea, the scyphomedusa, Chrysaora melanaster is among the most common gelatinous zooplankton in shelf waters 25 to 75 m in depth (Purcell et al. 2009).  In shallower waters, there was a more diverse community dominated by the delicate medusa Bolinopsis infundibulum, other small cnidarians, and ctenophore species occurred immediately underneath the sea ice (Purcell et al. 2009; Raskoff et al. 2010b).  Other common species include Sminthea arctica in the midwater depths, and Atolla tenella which was found in high abundance in the deep Canadian Basin (Raskoff et al. 2010b). 

Large populations of gelatinous zooplankton have been observed throughout the Arctic, particularly in at convergences, fronts, and polynyas (Ashjian et al. 1997).  In such areas, medusa and ctenophores can have a substantial grazing impact.  In the eastern Canadian high Arctic, the ctenophore Mertensia ovum was estimated to consume up to 9% per day of the C. hyperboreus population and 3-4% of the C. glacialis population.   Other prey items included hyperiid amphipods, pteropods, and smaller copepods.  Other food resources for gelatinous zooplankton include detritus and algal cells and in some cases small or juvenile fish (e.g. larval capelin and herring; Raskoff et al. 2010b).

Unlike the Antarctic, euphausiids are not abundant in Arctic waters.  However they can be difficult to accurately assess in ice-covered waters as they seek shelter in the pockets and fissures in the ice (Percy and Fife 1985).  Euphausiids are not considered to be a truly Arctic species, rather they are advected from the Bering Sea Water inflow (Suydam and Moore 2004) or from the Atlantic (Letessier et al. 2009).    The euphausiids Thysanoessa raschii and T. inermis were important prey items associated with bowhead whales in the western Beaufort Sea (Brinton 1962).  Euphausiids are found from the surface to the deep midwater pelagic areas, in depths greater than 500 m. 

Free-swimming amphipods are a key component of the Arctic food web, representing a link between zooplankton and higher level consumers such as fish, marine mammals, and birds.  Hyperiid and Lysianassid amphipods are among the common taxa found in Arctic waters and are a dominant component of the zooplankton abundance and biomass (Auel et al. 2002).  The hyperiid amphipod, Themisto libellula is a pan-Arctic species that can occur in high numbers in the ice free waters of the Arctic.  Based on the high amounts of C20:1 (n-9) and C22:1 (n-11) fatty acids and alcohols found in T. libellulatissues, their diet was domianted by Calanoid copepods.  Further analysis indicated a close association with ice-algal production.  This confirms field sampling data showing Themisto sp. associated wtih sympagic communities.

Themisto abyssorum is more closely associated with deepwater communties.  Themisto abyssorum is  considered to be a boreal species and is found in close association with the Atlantic Water that moves northward through Fram Strait.  Abundance generally decreases from east to west, dropping from >200 ind/m² over the contiental slope north of Spitsbergen to <40 ind/m² in the central Arctic (Auel et al. 2002).  It does not show a similar lipid signature seen in T. libellula, indicating that copepods are not a dominnant component of the diet.  Rather, the deepwater species is more likely an omnivore and scavenger.

Cyclocaris guilelmi, is also an epipelagic species, occurring in the deep-waters of the Arctic.  As wtih T. abyssorum, C. guilelmi appears to be Atlantic in origin but is found throughout the Arctic ocean.  Kraft (2012) found C. guilelmi to be a dominant component found in deepwater traps in Fram Strait.  The population appeared to be stable with peaks from August to February.

Cephalopods are a predator of and a key prey item for many of the VECs in the Arctic.  Squid move vertically through the water column, integrating marine resources throughout the pelagic environment.  The squid Gonatus fabricii is the most commonly reported species in the Arctic, with numerous records in the Atlantic sector, the Barents Sea and the high Canadian Arctic (Gardiner and Dick 2010). Berrytheuthis magister is the predominant squid species found in the Pacific domain.  Squid exhibit all manners of vertical distribution: near-surface dwellers (to 50 m), vertical migrators that either move into the surface waters at night or just move higher in the water column, and near-bottom dwellers.  In addition, some species exhibit ontogenetic descent moving progressively deeper as they age (Roper and Young 1975).  Cephalopods are voracious predators feeding on crustaceans, fish, other squids, and zooplankton.  Based on isotope analysis, squid are occupying different trophic levels in different regions (Navarro et al. 2013) indicating that squid are able to shift their diet based on availability.  The isotope ratios for Arctic squid indicated a trophic level of 3 to 5.  Squid are an important component of marine mammal and sea bird diets, including narwhals, White whales, walrus, murres and fulmars (Gardiner and Dick 2010).

Gelatinous zooplankton are poorly understood in the Arctic, largely due to the difficulty of capturing them with traditional sampling methods.  However, they are considered to be a substantial sink for primary and secondary production (Purcell et al. 2009).  In the Beaufort Sea, the scyphomedusa, Chrysaora melanaster is among the most common gelatinous zooplankton in shelf waters 25 to 75 m in depth (Purcell et al. 2009).  In shallower waters, there was a more diverse community dominated by the delicate medusa Bolinopsis infundibulum, other small cnidarians, and ctenophore species occurred immediately underneath the sea ice (Purcell et al. 2009; Raskoff et al. 2010b).  Other common species include Sminthea arctica in the midwater depths, and Atolla tenella which was found in high abundance in the deep Canadian Basin (Raskoff et al. 2010b). 

Large populations of gelatinous zooplankton have been observed throughout the Arctic, particularly in at convergences, fronts, and polynyas (Ashjian et al. 1997).  In such areas, medusa and ctenophores can have a substantial grazing impact.  In the eastern Canadian high Arctic, the ctenophore Mertensia ovum was estimated to consume up to 9% per day of the C. hyperboreus population and 3-4% of the C. glacialis population.   Other prey items included hyperiid amphipods, pteropods, and smaller copepods.  Other food resources for gelatinous zooplankton include detritus and algal cells and in some cases small or juvenile fish (e.g. larval capelin and herring; Raskoff et al. 2010b).