Executive Summary Section 1. The Physical Environment Section 2. Arctic Ecosystems and Valuable Resources Section 3. The Transport and Fate of Oil in the Arctic Section 4. Oil Spill Response Strategies Section 5. Biodegradation Section 6. Ecotoxicology of Oil and Treated Oil in the Arctic Section 7. Population Effects Modeling Section 8. Ecosystem Recovery Section 9. Net Environmental Benefit Analysis for Oil Spill Response Options in the Arctic

SECTION 2. ARCTIC ECOSYSTEMS AND VALUABLE RESOURCES

Quick Links to Section 2 Content

Summary and Key Messages Introduction Knowledge Status Habitats of the Arctic Summary of Arctic food webs Pelagic realm Benthic realm Sea-Ice realm VECs of Arctic marine environments Future Research Considerations Priority recommendations to enhance NEBA applications in the Arctic Links to Further Information Authors References Photos 2-1, 2-2, 2-3 Arctic field study (Jack D Word)

Summary and Key Messages

In order to minimize the potential impacts of an oil spill, valuable ecosystem components (VECs) that potentially become impacted should be indentified. Each compartment where oil might end up contains its own set of VECs with their own sensitivity and resilience to oil. Apart from the identification of VECs, their distributional patterns by life stage within environmental compartments (ECs) both in time and space are of importance. Except for the multi-year ice environments or species that are fixed to demersal or shoreline environments, the organisms and their young undergo seasonal migratory patterns with many species occupying Arctic ECs on a temporary basis. While these distributional patterns for migratory species and resident species are becoming better known, their locations during an oil spill needs to be characterized so that the optimum spill response options with the least amount of environmental consequences to VECs can be identified. Arctic specific VECs tend to congregate at

interface habitats like the surface layers at or near the air/water interface (SML), ice edges and under ice environments, polinyas, sediment/water in demersal nearshore and offshore locations, shorelines, and convergence zones for different water masses. Key topics for further study would focus on the importance of these interface habitats for the diversity and long and short term functioning of Arctic ecosystems. Once the main VECs have been identified, research should establish the seasonal distribution patterns of the life stages and population levels of VECs within each EC, especially within the interface environments. Resilience of VECs determines to a large extent the long term population level effects that would occur after an oil spill. For identified VECs a proper and generic resilience metric should be developed so that relevant information on VECs can be applied in net environmental benefit analysis (NEBA) decision making.

Introduction

The objective of this section is to compile existing information on the dominant organisms that comprise the communities associated with the Arctic marine waters and to identify the valuable ecosystem components (VECs). For the purposes of this review, a valuable ecosystem component (VEC) is a species of the marine ecosystem that is identified as having scientific, social, cultural, or economic importance. VECs may be determined on the basis of any or all of these important concerns. The VECs defined here are based on five qualities that include their importance in supporting the Arctic marine food webs, as well as ecosystem services. In addition, consideration is given to those species that may act as indicators of potential effects of oil spill response measures on the different ecosystem compartments. • Taxa that are important to the function of Arctic food webs: Certain taxa play a critical role in maintaining and supporting the ecosystems and other trophic levels, as well as supporting the ecosystem resources and function. For example, many species in each of the ECs of the Arctic rely on copepods and Arctic cod as a primary food source. The removal or reduction of populations of copepods, krill or cod would have a significant impact on ecosystem function in the Arctic, as well as impacting upper trophic levels that may represent the ecosystem services for that realm (e.g. traditional fisheries for Bowhead whales are supported by copepod and krill food resources). • Taxa that are representative of pelagic, benthic, deep-sea, and sea-ice realms: Taxa and age classes important to marine food webs in each of the primary ecosystem compartments were included as potential VECs. • Taxa that are relatively abundant: While abundance is not a core characteristic of keystone species, the removal or significant reduction in population levels of species that are relatively abundant or have a greater number of food-web linkages are more likely to impact ecosystem function than species that are less common or form fewer food web linkages. • Taxa that may have cultural or commercial importance: Ecosystem services are incorporated in VEC determinations. This can include both economic values (e.g. commercial fisheries) and social values. Arctic communities are tightly linked to ecosystem services with goods and services extending beyond typical economic values of natural resources. Most of the goods and services for Arctic communities have cultural and social values and are dependent on other food web components. While some of the traditional ecosystem services are captured here, often they are locally defined and may include species not listed here. • Taxa that are well suited to impacts analysis: Species that are well suited to experimental approaches for evaluating the effects of OSR alternatives were included in this list of VECs. This includes species for which there are toxicity testing methods that can or have been used to

evaluate effects at the individual or population level. Species characteristics for toxicity evaluations include sensitivity, availability, and the ability to withstand laboratory handling and stress. Copepods and Arctic cod are common test models for the Arctic.

Recently, there have been several notable international efforts to consolidate data to provide a more pan-Arctic understanding of the biological communities of the Arctic. As part of the International Polar Year (IPY; 2007-2008), specimen collections and data sets from numerous research institutes and government agencies were collated, reviewed and entered into a centralized database. As part of the CENSUS, the Arctic Organism Database (ArcOD) has allowed for pan-Arctic reviews of species distributions throughout the Arctic. The IPY was also the incentive for a number of research programs to address data gaps. The RUSALCA program is an international effort to better understand the environment of the Beaufort, Chukchi, Bering Strait, and Siberian system. This has included studies on circulation, benthic substrates, benthic and demersal communities, fish, zooplankton and birds and mammals. Similar efforts have been conducted in the Atlantic Sector, in the High Canadian Arctic and the Eurasian Arctic. The current review includes the findings of recent pan-Arctic studies and reviews, recent research programs, and peer-reviewed literature.

Knowledge Status

Habitats of the Arctic The Arctic marine waters generally include those waters above the Arctic Circle; however, the southern boundaries of the Arctic are variously defined by physical, biological, and political boundaries. For the purposes of this review, the Arctic will be defined in a manner consistent with the Arctic Ocean Diversity program and the Arctic Register of Marine Species (ARMS) which is based on biologically relevant physical criteria (areas within the seasonally average 2 °C surface isotherm or the median maximum sea-

Figure 2-1. The Arctic Region and Major Water Bodies (Map created by Brad Cole http://geology.com/world/arctic-ocean-

Figure 2-2. Bathymetric Features of the Arctic Ocean (Base map is from IBCAO http://www.ngdc.noaa.gov/mgg/bathymetry/arctic/) ice extent; Sirenko et al. 2011). Based on this definition, the Arctic includes the Arctic Ocean and associated coastal seas and bays bounded by the North American and Eurasian continental landmasses, including the northern portions of the Bering Sea, the Bering Strait, the Norwegian Sea, the Labrador Sea, Disko Bay, the Lincoln Sea, and Hudson Bay (Figure 2-1). The Atlantic portion of the Arctic is sometimes referred to as the Atlantic sector and includes the waters surrounding Greenland and Iceland, as well as the Norwegian Sea and into the Barents Sea, those areas most heavily affected by the advancement of Atlantic waters. The Arctic Ocean is a central deep ocean divided into four abyssal plains by prominent ridges surrounded by shallower continental shelves. The only deep water connection to the world’s oceans is through Fram Strait to the Norwegian Deep and Atlantic Ocean (Figure 2-2). A secondary connection to the Atlantic is through the Baffin Bay and the Labrador Sea and the Bering Strait, linking the Arctic Ocean to the Pacific. The shelves comprise nearly 50% of the area in the Arctic and are a dominant feature of the East Siberian, Laptev, Kara, and Barents Seas; the shelves are relatively narrow in the Beaufort and Chukchi Seas. Sandy and soft-bottom substrate dominates the Arctic, with finer silts and clays found in the outer shelves and deep basins. Coarser sand and gravel are predominant substrate on the inner shelf and nearshore areas. Although less common, there are notable and important harder substrate boulder fields and rocky intertidal areas, particularly in the vicinity of northern Greenland, Svalbard, and other island groups in eastern Canada. The predominant environmental influences on aquatic food webs in the Arctic are sea ice and light. A substantial portion of the Arctic Ocean is covered in ice throughout the year, while the adjoining waters are seasonally covered in ice with varying open-water periods coinciding with periods of 24h bright

Chukchi Shelf East Siberian Shelf Beaufort Shelf

Figure 2-3. Sea Ice Extent (National Snow and Ice Data Center, Boulder, CO) daylight. Approximately 14 to 15 million km2 of the Arctic region are covered in ice during the winter months (Figure 2-3). In the summer, the northernmost portions of the Arctic remain ice-covered (approximately 4 to 7 million km2). The lack of sunlight during the Arctic winter in combination with ice- covered waters limits primary production in Arctic waters, resulting in a period of low secondary productivity. The periods of low production are punctuated by periods of extremely high production during breakup and periods of open water in spring and summer. The combination of open water and long, bright days creates intense periods of primary production, grazing by primary consumers, and predation in the higher trophic levels. Whereas the aquatic communities are limited during the winter, the diversity and abundance of species increases dramatically in the summer. Thus the nearshore and open water communities vary considerably during these seasonal periods. A secondary effect of the breakup and snow melt periods is a shift in temperature and salinity, particularly in the nearshore areas. The Arctic waters are stratified throughout the year; however, the freshwater input from extensive river systems in the Russian and Canadian Arctic result in coastal corridors of estuarine to freshwater conditions during breakup. Nearshore species assemblages change throughout the open water season in response to the transition in salinity and water temperature. In many respects the Arctic seas are shared waters and as such have similar components in their aquatic food webs. However, regional differences and geographic isolation have also created some notable differences in the food web components. As in other oceanic basins, the Arctic region includes nearshore, pelagic, and deep-sea food webs. In addition, the Arctic includes communities associated with the annual and multi-year ice. An understanding of food webs and the key species (valuable ecosystem components) within those food webs allows is an important component of the environmental consequences analysis. Return to Quick Links

Arctic Food Webs Marine communities of the Arctic can be divided into three compartments or realms: the pelagic, benthic and sea-ice. While each of these compartments have a closely associated assemblage of organisms, they are linked to each other with many overlapping species. Our understanding of food webs and trophic linkages within the food web are built upon several different types of data. Direct observations of feeding behavior and stomach contents analysis are the most common types of information used to determine prey items and linkages. However, the ability to collect this type of data in certain habitats is difficult, particularly in Arctic and deep water environments. More recent methods have been developed that evaluate stable isotope ratios in tissues and in lipids. In the Arctic, the ratio of N13 and N15 has been an effective method for evaluating trophic levels. The presence of long-chained C20:1(n-9) and C22:1(n-11) fatty acids and alcohols has also been used as an indication of whether Calanoid copepods are a component of the diet. In this section we briefly summarize the food webs for each of these different realms and identify VECs for the Arctic marine ecosystems (Figure 2-4). Following this section, the components of each of these different food webs is discussed in more detail.

Pelagic Communities The pelagic food web is controlled by light and ice cover, altering the growth conditions for phytoplankton and the ability of surface-oriented predators to access prey. In early spring, increasing light and ice melt result in the release of ice algae into the water column and a dramatic increase in phytoplankton growth (Falk-Peterson et al. 2005). Some of the highest rates of primary production occur in these marginal ice zones (MIZ). While phytoplankton blooms are initiated by an increase in light, the magnitude and duration of the blooms are controlled by the nutrient concentrations (Tremblay et al. 2012). Nutrients increase in surface waters during the low production of the polar night and allow for the high production (approximately 50% of the total annual production) in the MIZ. The duration of the phytoplankton blooms is limited by nutrient availability and the decrease in light availability during the fall results in only one significant bloom event in the Arctic Ocean. The increase in open water and phytoplankton blooms begins in the boreal waters and progresses northwards towards higher latitudes over the spring and summer (Falk-Peterson et al. 2005). The predominant groups of phytoplankton include prasinophytes, diatoms, haptophytes, green flagellates, dinoflagellates, and chrysophytes, with blue-green algae (cyanobacteria) in the southern regions (Hsiao 1978, Sakshaug 2004; Li et al. 2009, Fujiwara et al. 2014). The zooplankton community in the Arctic is dominated by copepods, particularly the Calanoid copepods Calanus glacialis and C. hyperboreus. Both species are endemic to Arctic waters, with all life stages found in the Arctic (Sakshaug 2004). Calanus finmarchicus is a subarctic species that is found in the Atlantic domain, but does not reproduce in Arctic waters (Falk-Petersen et al. 2007). The diatom – Calanus food chain is considered to be critical to the overall production in the Arctic. Calanus spp. take advantage of early ice-algae blooms, continue feeding through the planktonic diatom blooms, converting low energy sugars into a high energy lipid reserves (Niehoff 2007). They create lipid stores that are rich in longer-chained fatty acids and alcohols; a characteristic that allows them to over-winter in a non-feeding state. The combination of rich lipid reserves and their large size make C. glacialis and C. hyperboreus a key prey item for higher level consumers throughout the Arctic. While less lipid rich and smaller in size, C. finmarchicus is a valuable food resource in the Atlantic sector, particularly the Barents Sea. Other pan-Arctic copepods include Oithona similis and Metridia longa. The subarctic species Neocalanus spp.,

Nutrients and detritus Nutrients and Detritus in water column in Snow and Ice

Benthic Algae Phytoplankton Sympagic algae and Kelp (pennate diatoms) (centric diatoms)

Benthic Invertebrates Zooplankton Sympagic Meiofauna Clams Calanoid copepods Amphipods Euphausiids Sympagic Copepods Echinoderms Hyperiid Amphipods Polychaetes

Jellyfish Baleen Whales Bowhead Minke Whale

Walrus Demersal Fish Sympagic Amphipods Bearded Seal Small Fish Sculpin Gammarus wilkitzkii Grey Whale Arctic cod Eelpouts Onismus spp. Grey Polar Cod Capelin

Nutrients and Detritus in Sediment Large Fish Greenland Seabirds Atlantic Cod Ringed Seal Halibut Waterfowl Arctic Char

Seabirds Narwhal Gulls White Whale

Orca Whale Polar Bear Arctic Fox Glaucous gull Skua

Humans

Figure 2-4. Arctic Food Webs

Eucalanus bungii, Pseudocalanus spp. and M. pacifica are found in the Pacific domain (Sakshaug 2004; Griffiths and Thomson 2002). Euphausiids (krill) are a subarctic herbivorous species that is abundant in portions of the Atlantic domain (Thysanoessa inermis) and in the Bering Strait-Chukchi-Beaufort region (T. longicauda and T. raschii; Suydam and Moore 2004; Letessier et al. 2009). While not as common as in the Antarctic, euphausiids are a key prey resource for higher-level consumers, in particularly the Bowhead whale (Brinton 1962). Other pelagic invertebrates that act as secondary consumers include amphipods, squid, and jellyfish. Hyperiid amphipods are large, free-swimming amphipods that feed on both smaller zooplankton and Calanoid copepods (Auel et al. 2002). The species Themisto libellula is a pan-arctic species found associated with sea-ice and shelf waters, whereas the species T. abyssorum and Cyclocaris guilelmi are more closely associated with outer shelf and deep waters of the Arctic (Auel et al. 2002; Kraft 2012). Second to copepods, hyperiid amphipods are a common food item for fish, seals, and birds. The squid, Gonatus fabricii is abundant in the Arctic and subarctic waters of the North Atlantic, with the squid Berryteuthis magister more commonly found in the Pacific Siberian-Chukchi waters (Gardiner and Dick 2010; Roper and Young 1975). Squid are agressive predators and can move easily from the surface to deeper waters of the Arctic, being an important vertical integrator of marine food webs (Navarro et al. 2013). Arctic squid are an important prey item for narwhals (Monodon monoceros), White whales (Delphinapterus leucas), porpoise, and some seals. Jellyfish are common in Arctic waters and can occur in abundance, representing a important consumer of zooplankton (Gardiner and Dick 2010). Throughout the Arctic, Arctic cod (Boreogadus saida) and Polar cod (Arctogadus glacialis) represent a critical link between the zooplankton community and higher trophic levels (e.g. seals, toothed whales). Both species are truly pan-Arctic occurring in all marine waters of the Arctic and are widely distributed throughout the Arctic, occupying nearshore, pelagic, and sea-ice habitats, residing both at depth and near the surface waters, depending upon age and season (Breines et al. 2008; Madsen et al. 2009). Both B. saida and A. glacialis can be found in small numbers or in large, densely packed schools. The primary prey for the Arctic gadids is Calanoid copepods and hyperiid amphipods (Sufke et al. 1998; Lonne and Gulleksen 1989; Bradstreet and Cross 1982; Frost and Lowry 1984). Capelin (Mallotus villosus) are also an important secondary consumer throughout the Arctic, particularly in the Barents Sea where they are the primary link between C. finmarchicus and Atlantic cod (Gadus morhua; Blanchard et al. 2002; Hamre 1994; Mehl and Yaragina 1992; Titov et al. 2006). Capelin are energy dense fish that move throughout the more estuarine nearshore waters and the Arctic waters. Arctic and polar cod, capelin, and herring are important food resources for higher trophic levels including larger fish (e.g. Atlantic cod), marine mammals, and birds. Anadromous fish are primarily found in the sub-adult and adult stages in the nearshore brackish waters of the Arctic. Arctic char are circumpolar and can be numerous in waters of the Russian Arctic, where lower salinity waters extend across much of the shelf (Craig 1984; Mecklenburg et al. 2011; Sherman and Hempel 2008). Cisco (Coregonus spp.) and salmonids will also use the nearshore zone during periods of high river flow and ice melt. Anadromous fish feed on a variety of nearshore resources including benthic copepods and amphipods, herring and capelin (Dunton et al. 2012). They represent an important prey resource for marine mammals and humans while in their freshwater habitats. Pelagic fishes of the Arctic deep water regions are not as well understood as nearshore and shelf species. Studies that have focused on deep waters have found that Arctic cod are numerically important throughout the year, with some stratification by water properties and by age group (Geoffrey et al. 2013; Parker-Stettner et al. 2011). Other midwater and deep water fishes common in other oceanic basins have been observed in the Arctic, including Myctophids and Gonostomidae (Reist and Majewski

2013; Dolgov et al. 2009; Jorgensen et al. 2005). The diel vertical migration patterns observed in other systems may not occur throughout the year in the Arctic due to the polar day and night.

Benthic and Demersal Communities Benthic communities in the Arctic are influenced by substrate type, presence and interaction with seasonal or permanent ice, salinity and temperature. Intertidal and nearshore subtidal communities are often limited by direct contact with ice, seasonal freezing of soft substrates, and scouring and scraping behavior of melting ice. Additional limitations in community diversity and abundance in the nearshore environments are highly variable salinities in areas influenced by large river systems in the Beaufort, Barents, Kara, and Laptev seas. Soft substrates dominate the Arctic seas, with silts and clays occupying the deep water basins and the outer shelf; fine sands and silts are common across the shelf, while coarser sands and cobbles limited to isolated portions of the shelf and the nearshore zone. Benthic macrofauna in the Arctic, like most oceanic basins, are dominated by polychaetes, bivalve mollusks, crustaceans (e.g. amphipods and isopods), and echinoderms. In the nearshore and inner shelf communities, Arctic mollusks often define the benthic communities and are a key prey item for higher trophic levels (e.g. walrus, bearded seals). The salinity tolerant bivalve clam Portlandia arctica is a dominant species in nearshore zones and is able to rapidly repopulate areas of disturbance. The Greenland cockle, Serripes groenlandicus, is a common circumpolar bivalve found up to 100 m depth on a variety of substrates and is a main component of the diet for walrus and bearded seals. Macoma calcarea is also a common component in Siberian-Chukchi-Beaufort and Barents-Kara-Laptev shelf communities, as well as in the fjords of northern Canada and Baffin Island (Grebmeier and Cooper 2012; Denisenko 2007; Filatova and Zenevich 1957). Other dominant clams in the shelf include Astarte sp., Mya truncata, Tellina sp. and Yoldiella solidula. In deep water benthic habitats, bivalves are smaller and less common, with species that are common to other oceanic regions (Axinopsida, Nucula, and Nuculana. As with clams, amphipods play an amplified role in the benthic communities of the Arctic, relative to other oceanic regions. Arctic amphipods include both infaunal and epifaunal species. The most widely distributed species across the Arctic are Ampelisca eschrichti, Anonyx nugax, Arrhis phyllonyx, Gammarus setosus, and Byblis gaimardi (Piepenburg et al. 2011; Dunton et al. 2012). Of particular interest are the Lysianassid amphipods; a species rich group of epibenthic omnivorous amphipods that are key scavengers in the Arctic and deep sea waters. Many are especially adapted to scavenging with specialized mouthparts and extendable guts for food storage. In shallower waters, Lysianassid amphipods may have a more diverse diet. Lysianassid amphipods are domenate invetebrate macrofauna in certain environments. On tidal flats, Onisimus litoralis constitutes up to 95% of the macrofaunal density (Weslawski et al. 2000). Polychaetes are among the most abundant infaunal species of the shelf and deep water benthos throughout much of the Arctic (Bluhm et al. 2011). Species that represent the Arctic shelf are species observed in temperate habitats and include Maldane sarsi, Spiochaetopterus sp., Chone sp., Lumbrineris sp., Capitella capitata, and Eteona longa (MacDonald et al. 2010; Renaud et al. 2007). Echinoderms in the Arctic are the dominant epibenthic megafauna, with ophiuroid brittle stars occurring throughout the shelf. Dense aggregations of brittle stars can be found in areas of organic enrichment, such as polynyas (Piepenburg et al. 1997). The sea urchin, Strongylocentrotus droebachiensis is also found in Arctic waters and is an epibenthic omnivore, often grazing along the bottom of rocky or soft substrates. Decapod crustaceans are less common in the Arctic and are primarily represented by the shrimp Pandalus borealis and Pandalopsis dispar and the crab Chionoecetes spp. and the Red king crab (Paralithodes camtschaticus; Bluhm et al. 2009; Iken et al. 2010; Olav and Ivanovo 1978).

Epibenthic or demersal fish communities in the Arctic are dominated by sculpins (Cottids) and eelpouts (Zoarcids); taxa that are speciose, eurybathic, and pan-arctic (Mecklenberg et al. 2011). Arctic cod are also an important demersal fish found associated with the benthic zone at all depth ranges (Reist and Majewski 2013). The genera Myoxocephalus and Lycodes are genera that well represented in the Arctic (Mecklenburg et al. 2011). The Arctic flounder (Pleuronectes glacialis) and the Greenland halibut (Reinhardtius hippoglossoides) are also important epibenthic predators. Demersal fish generally feed on benthic infauna, as well as small or juvenile fish. Common predators include seals, birds, and some larger fish. As such demersal fish act as a link between benthic infauna and epifauna and higher trophic levels (Dunton et al. 2012).

Sea-ice Communities Sympagic communities include those organisms that live in close association with sea-ice. In some cases, species are obligate to the sea ice, but many are representatives of the pelagic or benthic community that have a portion or all of their life cycle in the ice (Melnikov 1997). There appear to be differences between the seasonal ice communities and those that inhabit the permanent ice. However, to a great extent the species assemblage appears to be similar with differences in abundance and biomass. Brine channels that form in the ice-water interface create a protected environment for an algal community dominated by pennate diatoms (Melnikov 1997; Sakshaug et al. 2010). Harpacticoid and cyclopoid copepods are the primary consumers of the ice-algae moving within the brine channels as well as along the ice bottom (Kramer 2010). The sympagic amphipods (Gammarus wilkitzkii, Onismus spp. and Apherusa glacialis) represent a critical link between the sympagic algal and copepod communities and higher trophic levels (Hop et al. 2000; Melnikov 1997; Arndt and Swadling 2006). The herbivorous amphipod, A. glacialis, is a primary food source for the Little auk, Alle alle. Both G. wilkitzkii and Onismus spp. are motile predators that feed on the sympagic copepods and are important prey items for fish (e.g. cod) and sea birds. The amphipod G. wilkitzkii has a life span of up to six years and generally prefers multi-year ice (Arndt and Swadling 2006). Sea ice provides a productive substrate and protective shelter. As such there are a number of pelagic or benthic species that spend a portion of their life in close association with sea ice. Pelagic copepods will perform diel migrations to feed at the ice-water interface, particularly during the ice melt when the ice algae and early season phytoplankton blooms can account for more than 50% of the copepods lipid reserves (Melnikov 1997; Arndt and Swadling 2006). One and two-year-old Arctic and polar cod find shelter in the shelves and fissures of the sea-ice, feeding on sympagic amphipods and pelagic copepods (Lonne and Guilliksen 1989; Gradinger and Bluhm 2005). Adult fish are seldom observed in close association with the sea ice (Hop et al. 2000). Ice amphipods and cod are subject to strong predation by top carnivores including seals and sea birds.

Mammals and Birds Arctic mammals include species associated with the sea ice and pelagic species. Ice seals include Ringed seals (Phoca hispeda) that feed primarily on cod and hyperiid and sea-ice amphipods when young, Bearded seals (Erignatus barbatus) that feed on clams, and Hooded (Cystophora cristata) and Harp (P. groenlandica) seals that feed on cod, capelin, squid and pelagic amphipods (Bradstreet and Cross 1982; NAMMCO 2005a). Walrus are found in the Bering-Chukchi, the Laptev Sea, and in the Barents- Greenland-High Canadian Seas (NAMMCO 2005b). Walrus feed primarily on clams of the inner continental shelves (Outridge et al. 2003; Bluhm and Gradinger 2008). Whales of the Arctic include both baleen and toothed whales. Bowhead whales (Balaena mysticetus) feed on copepods and euphausiids in the open Pacific and Atlantic waters (Rice 1998; NAMMCO 2005c). The White, narwhal, and Orca

(Orcinas orca) whales are the dominant toothed whales of the Arctic. White whales and narwhals feed primarily on cod and capelin. Arctic seabirds are dependent on Arctic marine resources for all or most of their energy requirements while they are in the region. Most seabirds are migratory arriving as spring blooms and breakup begins. Arctic birds that forage in the open pelagic are mostly alcids, gulls, skuas, and terns (Huettmann et al. 2011). Other taxa tied to marine food webs are sea ducks, most notably eider ducks.

Communities of Special Significance Polynyas, estuarine lagoons, and rocky substrate habitats represent important but less common habitats in the Arctic. The species that occur in these areas are not necessarily unique in Arctic or boreal waters, but they are found either in great abundance or in an assemblage of species that are well adapted to that habitat. Polynyas are openings or leads in the sea-ice that form due to currents or water temperatures generally in nearshore areas. They are a seasonal feature that allows light to penetrate into the water column and allows for direct access of the water surface in the absence of ice. Narwhals remain in close association with pack ice and congregate in great abundance in polynyas using this time for most of their annual feeding. Pelagic copepods and fish also congregate in these areas. Sediments associated with polynyas are highly organically enriched during the polar winter, and the abundance and biomass of the more motile components of the benthic community respond with increased abundance and biomass; strong evidence for pelagic-benthic coupling. Estuarine lagoons also represent another productive ecosystem, receiving organic input from terrigenous sources (e.g. riverine systems). Estuarine benthos (including amphipods, polychaetes, benthic copepods, clams, and snails) in lagoons are protected from ice or ice scour, enabling them to take advantage of organically enriched sediments. In response to the protected habitat and enriched benthic communities, epibenthic fish use the lagoons as feeding and nursery grounds. Anadromous fish, particularly char, cisco, and salmonids will move along the brackish nearshore zone as young adult and adult fish, taking advantage of the availability of food resources. As salinities increase in the lagoons, pelagic invertebrates and small fish will move into the protection and production of the lagoons. Finally, the productive lagoons are an important feeding ground for sea birds, in particular Eider ducks. Rocky substrate is less common in the Arctic, predominantly occurring in the Atlantic region of the Arctic. The communities associated with rocky intertidal and subtidal habitats are generally similar to those that occur in the northern Atlantic, with brown macroalgae (e.g. Fucus and Laminariales), barnacles, serpulid worms, mussels, and motile scavengers such as amphipods. Hard substrate in the deep sea occurs along the ridges, however, there is currently little data associated with the fauna on the Arctic ridges.

Pelagic Realm The pelagic environment includes those waters associated with the nearshore zone, the continental shelf and the deep water basins of the Arctic. The distribution of pelagic fish and invertebrates is defined largely by salinity, temperature, and light. In the extensive shelf waters of North America and the Russian Arctic there are two distinctly different bodies of water, the nearshore brackish waters and the Arctic Surface Water (ASW) or Atlantic Water (AW; Craig 1984). The occurrence of a shore-parallel band of turbid, warmer (5-10°C) brackish (10 - 25‰) water is a characteristic feature of the Arctic coastlines (Craig 1984). The ASW includes all open waters, extending a depth of approximately 100 m. The ASW is typically colder (-1° to 10° C) and more saline (28‰ – 34‰) than the nearshore waters.

Underlying the ASW is the Arctic Intermediate Water (AIW), layers of denser and colder waters that extend from approximately 75 to 450 m (lower). The shallower portions of the AIW tend to have temperatures <2°C and salinities ranging from 34.7 to 34.9‰. The deeper portions of AIW have temperatures that are 0-3°C and salinities greater than 34.9‰. During certain portions of the year, the deeper water may be slightly warmer than the shallower waters, with pelagic species using the deeper water as refuge from colder waters. AW on the other hand, pushes northward into the Arctic during the spring and summer months. Temperatures in the Eurasian Arctic increase as AW pushes northward in the spring and summer months. This push of AW is an important transport mechanism for larval dispersal and for boreal species to enter the Arctic. The Arctic Deep Water (ADW) occupy the abyssal basins of the Arctic, with stable environmental conditions with temperatures ranging from -2°C to -10°C and a salinity of 34.9‰.

Phytoplankton The phytoplankton population and primary production in Arctic waters are controlled primarily by light and nutrient availability. Ice cover limits light availability in the water column throughout the winter season. Phytoplankton blooms develop as the ice opens, with propagation of the algal bloom following along a latitudinal gradient from the southern Barents Sea in March – April to August – September in the Fram Strait and Arctic Ocean (Figure 2-5). Figure 2-5. Timing of Plankton Blooms in Once the ice recedes, there is a gradual increase the Arctic Oceans. in phytoplankton abundance (Falk-Peterson et al. From Falk-Petersen et al. 2005 2007). While light controls the timing and seasonality of primary production in the Arctic, the bloom duration and seasonal production are controlled by nutrient availability (Tremblay et al. 2012). Nutrient limitations in the Arctic are exacerbated by a persistent stratified water column, caused by salinity and temperature differences resulting from riverine input and melting pack ice. The nearly permanent stratification limits replenishment of nutrients from deeper, nutrient rich waters (Hsiao 1978). Chlorophyll-a estimates indicate that phytoplankton abundance is highest in the nearshore band, gradually decreasing with distance from shore. Unlike population cycles in more temperate waters, conditions in the Arctic do not allow for a second phytoplankton bloom during the late summer. Although nutrients in the water column slowly recover with periodic upwelling events, solar radiation begins to decline rapidly following the equinox. With the combination of short periods of light and nutrient limitations, primary production in the high Arctic is among the lowest in the world. The highest primary production is found in areas with energetic mixing with deep waters (Figure 2-6; Bering Strait, Fram Strait and the Atlantic sector). Nearshore and shelf areas having variable production depending upon the extent of stratification and import of nutrients from terrestrial sources (Tremblay et al. 2012; Carmack et al. 2006). Phytoplankton in the Arctic includes prasinophytes, diatoms, haptophytes, green flagellates, dinoflagellates, and chrysophytes, with blue-green algae (cyanobacteria) in the southern regions (Hsiao 1978, Sakshaug 2004; Li et al. 2009, Fujiwara et al. 2014). Recent field investigations have documented the distribution and potentially changing functional roles of picoplankton (<2µm) and nanoplankton (2- 20 µm) due to changes in sea ice coverage in the Arctic Ocean (e.g. Coupel et al. 2012). The Sea of

Figure 2-6. Annual Primary Production in Arctic (gC/m2/year) [Source: Carmack et al. 2006] Okhotsk and western Barents Sea are the most speciose regions, with the deep Arctic Ocean having the fewest species (Melnikov 1997; Sakshaug 2004). Diatoms and flagellates are most abundant, followed by lower densities of dinoflagellates and chrysophytes. Centric diatoms are the most common planktonic diatoms, with Chaetoceros spp. and Thalassiosira spp. associated with spring blooms. Pennate diatoms are less common in the phytoplankton, but are dominant in the ice-algal community. The microplankton Phaeocystis is also common throughout the sub-Arctic coastal basins and can form blooms of several billion cells per m3 (Sakshaug 2004) Flagellates were more predominant at offshore stations in colder, less turbid water and lower nutrient concentrations (Hsiao 1978). Horner (1984) found that in the western Beaufort both diatoms and flagellates were found in the open waters, with distribution controlled on a vertical rather than horizontal scale. Li et al. (2009) found that the nearshore phytoplankton community shifted from larger nanoplankton towards picoplankton and bacterioplankton with salinity and distance. The picoplankton community was dominated by the unique pan-Arctic, cold-adapted Micromonas. Sea-ice algae represent an important component of primary production, particularly in regions with permanent ice. The ice algae community is discussed more fully in later sections. However, it is important to understand that the spring blooms of ice algae precede the phytoplankton community and provide a critical food source for zooplankton.

Zooplankton Copepods and euphausiids represent the most important zooplankton group in terms of energy transfer to upper trophic levels (i.e. Arctic cod, birds, baleen whales). Among the large copepods (1-5 mm adult size), the Calanus species Calanus hyperboreus and C. glacialis are dominant throughout the Arctic region. The subarctic species Calanus finmarchicus and Oithona atlantica are also common in Atlantic Water and adjacent coastal waters (Sakshaug 2004). While not considered to be an Arctic species, C. finmarchicus, it is widely distributed across the Arctic by the northern Atlantic current that moves

northward along the Norwegian coast through Fram Strait and into the Barents Sea and onto the Arctic Ocean (Falk-Petersen et al. 2007). Other pan-arctic copepods include O. similis and Metridia longa. In Pacific waters Neocalanus spp., Eucalanus bungii, Pseudocalanus spp. and M. pacifica are also common in the Pacific Water (Sakshaug 2004; Griffiths and Thomson 2002). Smaller copepods dominate the brackish shelf waters Russian Arctic including Limnocalanus macrurus and Drepanopus bungei (Peters et al. 2004). Herbivorous krill are also an important component of the pelagic food web throughout the Arctic. The euphausiids Thysanoessa raschii and T. inermis are common in the Pacific and Atlantic arctic, with T. rachii also numerically important in the middle and Coastal Bering shelf. In the subarctic Atlantic, T. longicauda can be common; whereas T. longipes and Euphausia pacifica are more common in the Pacific Waters. Both T. longipes and E. pacifica are important prey items associated with bowhead whales in the western Beaufort Sea (Brinton 1962). The diatom – Calanus food chain is considered to be critical to the overall production in the Arctic (Falk- Petersen et al. 2007). Calanoid copepods comprise 50% to 80% of the mesozooplankton biomass in the Arctic. Calanus spp. take advantage of early ice-algae blooms and feed through planktonic diatom blooms, converting low energy sugars into a high energy lipid reserves. Calanoid copepods create lipids that are rich in longer-chained fatty acids and alcohols; a characteristic not shared by other smaller copepod species (Peters et al. 2004). The combination of rich lipid reserves and their large size make Calanus spp. a key prey item for a number of higher level consumers, in particular Arctic cod. While the three dominant calanoid copepods co-occur, they differ in their life histories. Calanus hyperboreus is the most polar species and is most common in the deep sea areas of the Arctic, including the Arctic Ocean, Fram Strait, and the Greenland Sea. It is a large copepod (4.5-7 mm) that can overwinter at depths of 500 m to 2000 m (Falk-Peterson et al. 2007). C. hyperboreus has a 2-yr life span during periods of high productivity which can extend to 3 to 5 years during periods of extensive ice cover. Calanus hyperboreus reproduce in deep waters in the winter/spring prior to the phytoplankton blooms (Niehoff 2007) with the naupliar forms developing just under the ice surface, feeding on sympagic (ice-associated) algae. Egg releases in early March appear to provide a lipid-rich food source prior to significant primary production (Darnis et al. 2012). Calanus glacialis is a smaller copepod (3-4.6 mm) that is found primarily on shelf waters of the Arctic. C. glacialis has a life span of 1-3 years, spawning throughout the Arctic prior to the yearly spring bloom. Most larvae reach the C1 copepod stage (early adult form) by ice break up allowing the nauplii to feed on ice algae in the relative protection of the pack ice (Falk-Petersen et al. 2007; Niehoff 2007). The C1 copepods are then able to take advantage of the phytoplankton blooms in early summer. It descends to deep areas on the shelf (200-300 m) to enter diapause and over winter (Falk-Petersen et al. 2007). Calanus finmarchicus is the smallest of the three Calanus species (2-3.2 mm) and has less lipid-rich reserves. While nauplii and copepodites may be advected into the Arctic Ocean and other northerly waters, C. finmarchicus does not appear to reproduce in Arctic waters (Niehoff 2007) but relies more heavily on reliable ice-algal blooms for reproduction. As with other calanoid copepods, C. finmarchicus release eggs prior to the phytoplankton blooms, which develop during the Arctic summer prior to over wintering at depths of 500 to 2,000 m (Falk-Petersen et al. 2007). In late-spring/early summer, reproduction rates for other copepods and euphausiids increase following blooms of phytoplankton, microzooplankton, and small copepods (Pseudocalanus spp.). Omnivorous zooplankton, such as Metridia longa feed on both living plankton, as well as the organic carbon spikes following blooms. Reproduction in such species appears to be more independent of the plankton blooms.

Neuston Neuston refers to a community of microbial, plant (phytoneuston) and animal (zooneuston) species that live at the water’s surface. Surface communities include obligate species that are in the surface layer throughout their life cycle, as well as facultative species that occupy the surface only during larval stages. Arctic neuston have a number of adaptations that allow them to live in the harsh surface environment, including oil droplets to shield them from ultra violet (UV) exposure and keep them at the surface, and diel migrations that help them compensate for the temperature extremes (Zaitsev 1971). While large temperature fluctuations and extreme UV exposure limit species diversity, marine phytoneuston abundance per unit volume may be a thousand times higher than the underlying bulk water populations (Zaitsev 1971; Word et al. 1986). Marine phytoneustonic communities are dominated by small diatoms and flagellates. As with abundance, the production per unit volume can be many times that of the underlying water. The zooneustonic community in Arctic waters include chaetognathans, copepods, euphausiids, hyperiids, and in smaller numbers of rotifers, pontellids, cladocerans, decapods, and fish larvae and eggs (Zaitsev 1971). Microbial populations, including bacterioneuston, may be 10,000 times denser than bacterioplankton populations (Hardy 1982; Sieberth 1971). The neuston community is somewhat self-contained, with zooneuston feeding on phytoneuston. Neuston is an important component of the pelagic food web, with zooplankton, fish, birds, and marine mammals feeding at the surface, particularly along convergence zones where the surface populations are highest (Zaitsev 1971). Bowhead whales, as well as other baleen whales, have been observed skim- feeding at the surface (Koski and Miller 2002).

Other Pelagic Invertebrates 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. libellula tissues, 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).

Fish For the purposes of this review, fish in the Arctic can be divided into four general groups, the pelagic shallow and midwater species, anadromous species, and demersal fishes. The bottom fish include nearshore, shelf, and deep water species. Pelagic fish are the least diverse group representing 13% of the 242 recorded Arctic species (Bluhm et al. 2011; Mecklenberg et al. 2011). There are 31 species considered to be anadromous. The remaining species are marine demersal fish.

Pelagic Fish Throughout the Arctic, gadoids (cod) represent a critical link between the zooplankton community and higher trophic levels (e.g. seals, White whales). Arctic cod (Boreogadus saida) and Polar cod (Arctogadus glacialis) are truly pan-arctic species occurring in all marine waters of the Arctic. Cod are widely distributed throughout the Arctic, occupying nearshore, pelagic, and sea-ice habitats, residing both at depth and near the surface waters, depending upon age and season. Both B. saida and A. glacialis can be found in small numbers or in large, densely packed schools. In the scientific literature there is confusion on the common names “Arctic cod” and “Polar cod” at times referring to either B. saida or A. glacialis. While these species are similar in appearance and life history, gene sequencing has shown that they are genetically distinct (Breines et al. 2008; Madsen et al. 2009). Both B. saida and A. glacialis have a diet dominated by pelagic or sympagic components (Sufke et al. 1998; Lonne and Gulleksen 1989; Bradstreet and Cross 1982). Stomach contents of B. saida cod sampled in the pelagic ranges of the Beaufort Sea, northern Canadian waters, and the Barents Sea were dominated by calanoid copepods and gammarid amphipods. Other prey items included hyperiid amphipods, mysids, and shrimps (Frost and Lowry 1984; Lonne and Gulliksen 1989). A similar pelagic diet was observed for A. glacialis in the Northeast Water Polynya near Greenland (Sufke et al. 1998). In the nearshore zone, the diet is dominated by copepods, gammarid amphipods, and young-of-the-year Arctic cod. Both B. saida and A. glacialis spawn under the ice in the winter months; however recent observations indicate that there are regional differences in the hatching season of B. saida (Figure 2-7). Bouchard and Fortier (2011) noted that cod hatching started as early as January and extended to July in areas with significant freshwater input (Laptev/East Siberian Seas, Hudson Bay, and Beaufort Sea). In contrast, hatching was restricted to April-July in regions with little freshwater input (Canadian Archipelago, North Baffin Bay, and Northeast Water). The authors found that the different hatching periods resulted with different length and weight classes co-occurring throughout the Arctic. Cod larvae generally occupy a depth of 10 – 30 m, settling to the bottom in September (Craig 1984; Graham and Hop 1995). As noted above, the distribution of B. saida and A. glacialis includes nearly all marine waters of the Arctic depending upon the age class and the season. Arctic cod have been found to be a dominant component of both the pelagic and demersal communities at all depths; cod have been collected from the mixed water mass (<200 m), at the sharp halocline (200-300 m), and in the deeper Atlantic water mass (>300 to 1000 m; Reist and Majewski 2013; Norcross et al. 2012). One and two year old fish also occupy fissures and gaps in the ice pack, feeding on the sympagic fauna. In the summer months, adult cod are dispersed in habitats ranging from coastal brackish waters to the demersal and pelagic zones of the shallow shelves, including the ice-water interface (Craig 1984; Lonne and Gulliksen 1989; Gradinger and Bluhm 2004). In autumn, as nearshore salinities increase, large shoals of cod are observed in

shallow (<10 m) waters (Hop et al. 1997; Welch et al. 1993), presumably following shoreward fronts of plankton. Acoustic surveys conducted as part of the BREA program as well as others conducted in the US Beaufort have found large shoals of Arctic cod in the water column and near the bottom along the entire shelf of the Beaufort Sea (Geoffrey et al. 2013; Parker-Stettner 2011). There was a clear segregation between the young-of-the-year (YOY) and age 1+ fish in the summer months. Age 1+ fish were found to aggregate in the deeper waters of the shelf and slope at depths ranging from 200 to >1000 m while large shoals of YOY Arctic cod were found nearer to the surface (20 to 100 m) in nearshore waters extending into waters over the outer shelf and slope (Figure 2-8). The near bottom aggregations of

100 m YOY 200 m

300 m

400 m Age 1+

Figure 2-8. Arctic cod (Boreogadus saida) vertical distribution during the ice- free season along the Mackenzie Slope 2012 (from Geoffrey et al. 2013). Arctic cod at depths of 200 to 400 m appear to span the Canadian Beaufort shelf into the fall and winter months (Geoffrey et al. 2013; Benoit et al. 2008). Acoustic surveys during the winter months have found massive aggregations of adult cod at depths of 140 to 230 m under the pack ice in the Canadian Beaufort waters (Benoit et al. 2008) and at depths of 300 to 1,300 m near the North Pole (Geoffrey 2013). In winter months, adult cod appear to remain in schools at the deep inverse thermocline (160- 230 m, -1 to 0°C) throughout the Polar night to avoid seal predation; whereas smaller cod (<25 g) periodically migrate into the isothermal cold intermediate layer (90-150 m) to feed on Calanoid copepods and then return to the deeper layer (Benoit et al. 2010). An exception to the Arctic cod dominated pelagic food web is in the Barents Sea and White Sea. The Barents Sea is located between the Arctic and boreal oceanic systems and is influenced by the variations in the Atlantic current and the Polar front. In the southern portions of the Barents Sea, where the Atlantic water is more predominant, capelin (Mallotus villosus) is the primary link between pelagic crustaceans (e.g. copepods and amphipods) and higher trophic levels (Blanchard et al. 2002; Hamre 1994; Mehl and Yaragina 1992; Titov et al. 2006). The importance of capelin to the Barents Sea ecosystem was demonstrated when capelin stocks decreased markedly in the 1980s, resulting in decreases in stocks of the commercially important Atlantic cod (Gadus morhua) and ringed seals. Subsequent studies have demonstrated linkages between the location of the polar front, the population of capelin and subsequent changes in the population of Atlantic cod (Titov et al. 2006). Capelin are also an important forage fish in the northern boreal waters of Greenland, the Sea of Okhotsk and the Bering Strait. Unlike Arctic cod, Atlantic cod are more demersal in nature, generally feeding near the bottom. The diet of Atlantic cod is remarkably varied, with Mehl and Yaragina (1992) reporting with over 180 prey

species. While capable of feeding on a variety of invertebrate and vertebrate prey, capelins appear to be the primary energy source. Pacific herring (Clupea harengus pallasi) are another nearshore forage fish that represents an important link between zooplankton and higher level consumers, particularly anadromous fishes of the Bering- Chukchi-Laptev and Lofoten-Barents Sea systems (Mehl and Yaragina 1992; Hamre 1994). Herring feed primarily in the water column on copepods, euphausiids, and mysids. Herring spawn en masse and their eggs and larvae are a vital food source for nearshore migrating anadromous fish in the Arctic such as salmonids, cisco, and char. In the Arctic they are generally found in the nearshore waters and avoid the colder, Arctic water (Craig 1984). While numerically less important than the Arctic cod, capelin and herring are important forage species for upper trophic level consumers.

Anadromous Fish Anadromous fish include those species with a life history that includes both freshwater and marine habitats. In the Arctic, utilization of marine waters is typically limited to the brackish waters found in nearshore corridor immediately following breakup. Anadromous fishes in the Arctic include Arctic char (Salvelinus alpinus), least and Arctic cisco (Coregonus sardinella and C. autumnalis), broad and humpback whitefish (C. pidschian and C. nasus), Inconnu (Stenodus leucichthys), and several species of salmonids (Craig 1984; Mecklenburg et al. 2011). These species spawn in fresh water and typically do not enter coastal waters until months, or often years, after hatch. Thus, the most sensitive life stages for anadromous fish are spent in the Arctic rivers and lakes. Use of marine waters is limited to feeding and migration. Coregonids are the most common anadromous fish in the Laptev-Kara-East Siberian waters, with Arctic cisco more commonly found in the marine waters than Least cisco (Sherman and Hempel 2008; Craig 1984). Arctic char range widely from their stream of origin and might be found in more open water during high flow years (Jarvela and Thorsteinson 1999; Johnson 1980). When occupying the nearshore brackish water, anadromous fish feed nearly exclusively on epibenthic fauna (e.g. polychaetes, mysids, and amphipods; Dunton et al. 2012). In turn, anadromous fish become an important food source for seals as well as subsistence fishers. A number of salmonid species are found in river systems throughout the Arctic; however, their use of marine waters is limited. Atlantic salmon are the most common form found in the Lapotov-Barents Sea and Hudson Bay river systems (Sherman and Hempel 2008). Pink and chum salmon (O. gorbuscha) are the most abundant species of Pacific salmon documented in the Arctic, with populations in Russian (Yana and Lena Rivers), Canadian (Mackenzie River), Alaskan, and Norwegian waters (Sherman and Hempel 2008; Mecklenburg et al. 2002). With the exception of some juvenile use of the brackish nearshore waters, adults are the most common life stage found in marine waters.

Demersal Fish Demersal fishes are those that are found in close association with the bottom. Sculpins (Cottidae) and eelpouts (Zoarcidae) are the most speciose fish taxa in the Arctic, comprising over 50% of the species in polar waters (Mecklenberg et al. 2011). Both taxa are well adapted to living in the dominant substrates found in the Arctic (sand, silt, and mud), as well as rocky bottoms, with most species spending the majority of their life cycle in close association with the bottoms. Adults often deposit eggs directly on benthic substrates or on bottom oriented vegetation. Larval and early juvenile forms may remain on the bottom near the adults or move into the water column or into vegetation before descending to the bottom as young fish. Common and pan-Arctic sculpin species include the Arctic Staghorn sculpin (Gymnocanthus tricuspis), the large Short-horned sculpin (Myoxocephalus scorpius: 90 cm length), and Spatulate sculpin (Icelus spatula; Mecklenberg et al. 2011). Two genera account for most Arctic eelpouts, Gymnelus and Lycodes. Sculpin and eelpout diets vary, but many sculpin and eelpouts feed on

benthic infauna and epifauna, including polychaetes, benthic amphipods, small mollusks, and epibenthic crustaceans, with larger species feeding on fish, including cods, flounders, and smelts (Dunton et al. 2012). Anti-freeze proteins have been found in several species of Myoxocephalus sculpins, showing their adaptation to Arctic waters (Fletcher et al. 1982). Flatfishes or flounders live on the bottom, usually in shallow marine waters, and burrow into the surface sediment to rest and wait for prey. They eat worms, mollusks, echinoderms, crustaceans, other benthic invertebrates, and fishes. Arctic flounder (Pleuronectes glacialis) are a pan-Arctic species that prefer coastal and nearshore waters (Mecklenberg et al. 2011).

Deep-Sea Fish The deep-sea fishes are perhaps the poorest known group in the Arctic. Recently there have been several targeted efforts to sample the deep basins in the Arctic (Reist and Majewski 2013; Dolgov et al. 2009; Jorgensen et al. 2005). In the deep Canadian Beaufort, Arctic cod were the dominant species in the water column and associated with the demersal community (Reist and Majewski 2013). Other species found in midwater trawls included species found in other deep ocean basins, including Myctophids (lanternfish) and Gonostomids (bristlemouths). The myctophids, Benthosoma glaciale and Protomyctophium arcticum, spawn above the Polar front (Dolgov et al. 2009) and were found in deep water trawls (Riest and Majewski 2013). Other species have been recently collected from the Kara Sea, including Myctophum punctulum (Dolgov et al. 2009; Weinrroither et al. 2010). The wide-spread gonostomid, Cyclothone microdon, has been observed in trawls in Baffin Bay (Riest and Majewski 2013; Mecklenburg et al. 2011). Based on observations of myctophids and bristlemouths throughout the world, their diet is dominated by pelagic crustacean, migrating to the surface from depth to feed. It is not known if the diel vertical migrations occur in the Arctic. Deepwater demersal fish taxa are generally similar to those found in other oceanic basins and include Zoarcids (eelpouts) and Macrourids (grenadiers). The globally distributed macrourids, Coryphaenoides rupestris and Macrourus berglax have been found in the Baffin Bay (Jorgensen et al. 2005). The Glacial eelpout (Lycodes glacialis) is one of the most dominant demersal fishes in the Arctic basins. This large eelpout (~70 cm) moves along the bottom stirring up the bottom sediments to feed on small benthic crustaceans and mollusks; L. glacialis also feeds on other fishes and cephalopods (Mecklenberg and Mecklenburg 2011). This is a truly deep water species, spending its entire life cycle at depths >1,000m. The Greenland halibut (Reinhardtius hippoglossoides) is a right-eyed flounder typically associated with deep waters of the Arctic (200 – 1600 m), as well as deep waters of the Atlantic and Pacific Oceans. The Greenland halibut is epibenthic, and feeds on epibenthic crustaceans, demersal fish, and other invertebrates. Deepwater rays found in the southern Arctic waters in Alaska and Baffin Bay include Rajella spp. and Amblyraja radiata (Dolgov et al. 2009; Mecklenburg et al. 2002).

Marine Mammals Marine mammals are both permanent and seasonal members of the Arctic and include baleen and toothed whales, seals, walrus, and Polar bear. The following section focuses on those mammals closely linked to the marine food webs.

Bowhead Whale (Balaena mysticetus) Bowhead whales are circumpolar, residing in the high latitudes from late April to October. In the spring months, bowheads migrate northward as the sea ice breaks up. Five stocks have been identified, including the Spitsbergen, Baffin Bay-Davis Strait, Hudson Bay-Fox Basin, Sea of Okhotsk, and Bering- Chukchi-Beaufort stocks (Rugh et al. 2003). The latter stock overwinters in the Bering Sea. In the spring,

the Bowheads move north and east, past Point Barrow into the western Beaufort Sea (Lowry et al. 2004). The majority of whales move into the Canadian Beaufort Sea for the summer months; however, some Bowhead whales will either remain in the eastern Alaskan Beaufort or move into the Arctic Ocean. While Bowhead whales appear to favor continental slope waters in the spring and summer, they appear to favor the inner shelf waters (<200 m depth) of the western Beaufort in September and October (Moore et al. 2000). As the ice cover increases in late fall, the whales migrate into the Bering Sea for the winter months. Bowhead whales are considered to be second order consumers (Hoekstra et al. 2002), with a diet dominated by euphausiids and calanoid copepods (Bluhm and Gradinger 2008). Stomach content analyses indicate that, while benthic crustaceans and fish occur, their consumption is either occasional or incidental (Frost and Lowry 1984; Lowry et al. 2004). In the Bering-Chukchi-Beaufort system, there appears to be some seasonality in the diet which is dominated by euphausiids in spring and by copepods in the summer and autumn months. This distribution of diet is likely to be a result of opportunity, rather than selection. Dominant species in stomach contents included the euphausiids Thysanoessa raschii and the copepods C. hyperboreus and C. glacialis (Frost and Lowry 1984; Lowry et al. 2004).

White Whale (Delphinapterus Leucas) The White whale, or Beluga, is a circumpolar species inhabiting cold waters of the Arctic and subarctic waters (Rice 1998; NAMMCO 2005a). During the winter months, White whales retreat to subarctic regions with loose pack ice and winter polynyas (Barber et al. 2001). During the summer months, White whales live in coastal waters, estuaries, shelf breaks and deep basins. In the Alaskan Arctic, White whales move into the Beaufort Sea in May, moving east into the Canadian Beaufort or north to the Arctic Ocean for much of the summer (Loseto et al. 2006). In the fall as the Arctic cod congregate in the nearshore waters, White whales cross along the Alaskan mid-shelf in late August and September (Suydam and Moore 2004). The Eastern Chukchi White whale typically remains in the more open waters (>200 m depth) throughout the year, whereas the Eastern Beaufort Sea White whales move closer to shore when in the eastern Beaufort Sea (Suydam et al. 2001). White whales are considered to be third order consumers (Hoekstra et al. 2002), with a diet dominated by Arctic cod (B. saida and A. glacialis), and to a lesser extent whitefish (Coregonidae) in the Russian and Greenland Arctic. A variety of other prey items have been observed in stomach contents, including capelin, herring, smelt, sculpins, cephalopods and benthic invertebrates (Bluhm and Gradinger 2008). Nitrogen and carbon isotope signatures indicate that they also feed on copepods and euphausiids, particularly in the spring and fall (Hoekstra et al. 2002; Frost and Lowry 1984). Known predators of White whales include Orca whales, Polar bears, and humans (NAMMCO 2005a).

Narwhal (Monodon monoceros) Narwhal occur in the deep and offshore waters of the Canadian High Arctic, the Barents and Kara Seas, eastern Laptev Sea and the waters surrounding Greenland (Sherman and Hempel 2008). Narwhal appear to have high site fidelity, remaining in close association with the ice in winter. Winter feeding grounds appear to be more important than summer feeding areas, with remarkable aggregations of narwhals found in polynyas. In winter, a large number of whales can share the limited open water areas; near Greenland, between 17,000 and 19,000 narwhals were found to occupy 2% of the surveyed area (approximately 73 whales per km2 of open water (Laidre, personal communication). Narwhals feed mostly in deep water and possibly at or near the bottom. Dives of up to nearly 1,500 m and 25 minutes are documented (Laidre et al. 2003), and there are some seasonal differences in the depth and intensity of diving (Laidre et al. 2002, Laidre et al. 2003). Arctic cod (B. saida and A. glacialis) and the squid Gonatus fabricii dominate the narwhal diet, with lesser amounts of Greenland halibut and other deep-

sea fish (Laidre and Heide-Jørgensen 2005a; Bluhm and Gradinger 2008). Predators include Orca, Polar bears and humans (Hay and Mansfield 1989).

Ice Seals Ice seals of the Arctic include Ringed seals, Ribbon Seals, Spotted Seal, and Bearded Arctic seals. Ringed seals (Phoca hispida) are the most common and widely distributed ice seal in the Arctic (Reeves 1998). Ringed seals are relatively small seals (1.5 m) that are generally found on permanent ice or large floes, maintaining breathing holes allowing it to use ice habitats when other seals cannot (NAMMCO 2005b). Major foods eaten are Arctic cod, nektonic crustaceans (hyperiid amphipods and euphausiids), capelin, sculpin, and sea-ice and benthic crustaceans (Bluhm and Gradinger 2008). The balance of the diet varies seasonally. Ringed seals are a primary prey item for Polar bear, Arctic fox and Glaucous gulls (NAMMCO 2005b). The Bearded seal (Erignathus barbatus) is a solitary seal with a circumpolar distribution. It is most abundant where it can reach the sea bottom to feed. The bearded seal is generally found in the pack ice where openings are common since it cannot maintain a breathing hole. In the Beaufort and Chukchi system, E. barbatus consumed crab, shrimp, and clams (Lowry et al. 1980). In the Kara and Barents Seas, and Sea of Okhotsk bearded seals fed primarily on Arctic cod (B. saida) as well as shrimp (Sclerocrangon boreas) and mollusks (Finley and Evans 1983). In the areas of NW Greenland and the Canadian High Arctic, bearded seals had a varied diet including fish, crustaceans, gastropods, cephalopods and polychaetes (Finley and Evans 1983). Other seals that are found in the Arctic include Ribbon seals (Phoca fasciata), Harp seals (P. groenlandica), and Spotted seals (P. largha). Both the Ribbon and Spotted seals feed primarily on Arctic cod, capelin, as well as demersal fish and large benthic crustaceans. Harp seals feed primarily on Arctic cod and shoaling fishes, such as herring and capelin (Bluhm and Gradinger 2008).

Walrus (Odobenus rosmarus) Three subspecies of walrus occur in the Arctic: the Pacific walrus (O. rosmarus divergins) in the Bering- Chukchi), the Laptev walrus (O. rosmarus laptevi) in the Laptev Sea, and the Atlantic walrus (O. rosmarus rosmarus) in the Barents-Kara, Greenland, and High Canadian Arctic waters (NAMMCO 2005c). Walrus are extremely gregarious, often hauled out on land or ice floes, with several thousand individuals in a herd. Walrus feed in shallow waters (10-50 m), foraging through bottom sediments with their stiff beard bristles. Their primary diet appears to be dominated by bivalve clams, however, stomach contents analysis also indicates that other benthos are also important, including snails, echinoderms, and crabs (Outridge et al. 2003; Bluhm and Gradinger 2008). Dominant clam species found in stomachs included Mya truncata, Serripes groenlandica, and Macoma sp. Due to their size, tusks, and their gregarious behavior walrus predators are limited to Polar bear, Orca, and humans (NAMMCO 2005c).

Orca Whales (Orcinus orca) Orcas occur in the Arctic during open water periods. Orcas move northward from the Bering Sea or the North Atlantic. Distribution likely varies, with movements tracking those of favored prey species or pulses in prey abundance of availability (such as seal pups or fish runs). In the Arctic, Orcas rarely move close along or into the pack ice (Reeves et al. 2002). The frequency and abundance of Orcas in the Arctic appears to increase during years with decreased ice coverage. Orcas are a top predator and feed on a variety of large vertebrate prey including anadromous and pelagic fish, ringed seals, and whales. Orcas are considered a significant threat to Bowhead whales (COSEWIC 2009C).

Polar Bear (Ursus maritimus) Polar bears are linked to the marine habitat through diet and daily or seasonal migration. Although they reside on the ice during the winter, polar bears are accomplished swimmers and inhabit the open waters along the ice edge; they migrate toward land once the ice melts. Polar bears are linked to the marine pelagic food web, feeding primarily on ringed seals, although they will also feed opportunistically on other marine mammals (Thiemann et al. 2007).

Birds Arctic seabirds are dependent on marine resources from the Arctic for all or most of their energy requirements while they are in the region. Most seabirds are migratory arriving as spring blooms and breakup begins. Arctic birds that forage in the open pelagic are mostly alcids, gulls, skuas, and terns (Huettmann et al. 2011). Other taxa tied to marine food webs are sea ducks, most notably eider ducks.

Black-legged kittiwakes (Rissa tridactyla) Black-legged kittiwakes are one of the most numerous seabirds with a circumpolar distribution. Arriving in southern portions of the Arctic in February and moving northerly through April. Kittiwakes feed in ice floes as well as in open water, skimming the water surface or feeding from the surface. Based on stomach contents analysis from kittiwakes in Lancaster Sound, the summer diet is dominated by Arctic cod (93% to 98%; Bradstreet 1976). Dahl et al. (2003) indicate that kittiwakes in the vicinity of Svalbard feed primarily on capelin, Arctic cod, and hyperiid amphipods. A similar diet was observed in Barents Sea. Isotope analysis in the High Canadian Arctic indicated that amphipods may play an important role to fish over the course of the year (Hobson 1993).

Black Guillemots (Cepphus grille) Black guillemots are a common bird in open water and amongst the ice floes. Black guillemots are generalists. Stomach contents analysis in Lancaster Sound showed that amphipods, copepods, and Arctic cod were all important components in guillemot diets. Amphipods and copepods appeared to be a more dominant component of the diet when the guillemots fed along the ice edge in later spring to early summer (Bradstreet 1980), with fish being an important component of the diet throughout the year (Hobson 1993).

Thick billed Murres (Uria lomvia) Thick-billed murres or Brunnichs guillemots are members of the auk family (Alcids). Thick-billed murres over-winter in boreal regions where there are open waters. In summer, U. lomvia congregate and breed in the Chukchi Sea, the Siberian coast, eastern Canadian Arctic, Greenland and northern Norway. Murres are agile diving birds that consume both fish and crustaceans, with Arctic cod comprising the majority of the diet in both coastal and offshore ice edges (Bradstreet 1980; Hobson 1993). Summer diet was more variable feeding on pelagic amphipods when cod are unavailable. Murre chicks’ diet is dominated by Arctic cod and sculpin.

Northern Fulmar (Fulmarus glacialis) Northern fulmars are long-lived (32 years) migratory birds, moving northwards to the Arctic between May and July. Fulmars are pelagic birds, preferring shelf habitats, particularly shelf breaks or over the continental slope, though they are seldom further than 100 km from shore (Dewey 2009). As with many other sea birds, the fulmar diet is dominated by Arctic cod, copepods and pelagic amphipods. Fulmars also prey on the squid, Gonatus fabricii. Seasonal analysis showed that amphipods and copepods were

dominant in the diet of adult and nesting fulmars. Arctic cod are the primary diet once chicks have hatched and during rearing. After that time, amphipods (Hyperia sp., Gammarus sp, Themsto sp.) and copepods once again dominated the diet.

Common Eider (Somateria mollissima) The Common eider is a large diving duck common in the Arctic, particularly in the High Canadian and Atlantic sectors. Common eiders feed primarily on benthic prey including mollusks (Buccinum glacialis, Hiatella arctica), barnacles (Balanus balanus), decapods (e.g. Hyas araneus), and amphipods (Gamarellus homari; Dahl et al. 2003). Eiders are an upper level consumer in kelp forest (Fredriksen 2003) and estuarine lagoons (Dunton et al. 2012). Isotope analysis confirms that eiders feed at the lower trophic levels (Hobson 1993). Unlike other Arctic species, lipids analysis and stomach contents analysis show that copepods are not an important prey item for eiders. Return to Quick Links Little Auk/Dovekie (Alle alle) Dovekies are a small marine diving bird that is circumpolar in distribution (Day et al. 1988). This small auk overwinters in boreal waters, such as the North Sea and Norwegian Sea. In early spring they migrate northwards to feed on the sympagic copepods and amphipods (Dahl et al. 2003). The Little auk feeds on the herbivorous sea-ice amphipod, Apherusa glacialis (Kramer 2010). Dovekies also rely heavily on Calanus copepods, relying on the lipid rich C. glacialis and C. hyperborealis to successfully raise their chicks (Falk-Petersen 2007). Breeding colonies can be quite large with 30 million birds observed in northwestern Greenland.

Glaucous gull (Larus glaucescens) Glaucous gulls are pan-Arctic and are a primary avian predator in the Arctic that feed on a wide variety of fish, mollusks, crustaceans, eggs, chicks, and adult seabirds, as well as carrion. They will often prey on young and adult birds, as well as the catch from other birds. Arctic fox are important predators of gulls and skua, as well as other nesting birds, preying on eggs and chicks.

Arctic jaeger (Stercorarius parasiticus) Arctic jaegers are a top avian predator during the summer months, migrating annually to overwinter in the Antarctic. Jaeger primarily on fish, though they will also feed on insects and berries. While they can catch their own food, they will often steal fish from other birds. They will also prey on the nests of waterfowl, eating the eggs and young, as well as small mammals (e.g. lemmings).

Benthic Realm Benthic communities are strongly influenced by the substrate-type and sediment grain size. Benthic substrates in the Arctic are dominated by fine-grained sands, silts, and clays on the shelves and fine clays and silts in the oceanic basins (Bluhm et al. 2010). Sediment in the expansive shelves of the Barents, Kara, and Laptev Seas are typically dominated by fine grained sediments (Stein et al. 2004, Semiletov et al. 2011; Cochrane et al. 2009), with areas of sandy substrate occurring in the nearshore areas. Similarly the narrowing shelves of the Bering and Chukchi seas are fine in nature, with some sandy areas occurring in the Bering Strait. In the central reaches of Russian, Greenlandic, and Baffin Island fjords, sediments are dominated by very fine, unconsolidated clays and silts (Aitken and Fournier 1993, Stein et al. 2004). Sands and gravelly substrate is more common in the nearshore zone and in erosional areas. Hard substrate is localized and includes subtidal boulder fields as well as nearshore rocky outcrops. Notable examples are the boulder fields in the Beaufort Sea, portions of the Barents Sea, and the rocky shoreline in northern Greenland and Svalbard.

Intertidal Communities Intertidal benthic communities in the Arctic are generally thought to be less diverse than those found in lower latitudes due to ice scour and UV exposure. The disturbance from ice comes from direct contact of foot or anchor ice and scouring during breakup. Such disturbance results in a continually changing benthic community dominated by fast-settling, opportunistic meiofauna (Barnes 1999). Estimates suggest that Arctic intertidal macrofaunal communities typically have no more than 100 species, with some areas nearly devoid of intertidal macrofauna (animals larger than 0.5 mm). In contrast intertidal boreal communities in Alaska and Norway may have over 200 to over 300 species (Weslawski et al. 2011). Most intertidal species are circumpolar; however, their regional distribution can be highly variable. For example, areas of the Beaufort and Siberian coasts are devoid of intertidal macro- organisms as beaches are predominately gravelly with little stability and fast ice in the winter months (Weslawski et al. 2011). Conversely, estuarine lagoons along the Beaufort are relative benthic hotspots, with well-developed benthic infaunal communities that are protected from fast ice and coastal erosion (Dunton et al. 2012). Rocky intertidal and shallow subtidal communities are an important component in certain portions of the Arctic, particularly the Atlantic sector (Figure 2-9). Benthic communities in these areas are more akin to those of north Atlantic rocky intertidal and shallow subtidal habitats. For example, in the steep rocky substrate in Svalbard (Kuklinski and Barnes 2008) the most common species include the macroalgae Fucus spp., sessile (i.e., non-mobile) barnacles (Balanus balanoides), and motile gastropods (Littorina saxatilis) and amphipods (Gammarus setosus and G. oceanicus). Associated subtidal communities are dominated by the barnacle Balanus balanus, brittle stars (Ophiopholis sp.), motile amphipods (Calliopidae sp.), isopods (Munna sp. and Janira maculosa), sipunculid polychaete worms, and snails (Alvania sp.).

Figure 2-9. Locations with Shoreline Dominated by Hard Substrate (Red outline; from Lantuit et al. 2012)

In the western Arctic, hard-substrate communities are uncommon in intertidal and subtidal waters. However, there are isolated communities associated with patches of boulders and cobble. Dunton et al. (1982) characterized an Arctic kelp community associated with subtidal (<10m) boulder patches in the Alaskan Beaufort Sea. Exposed boulders and cobble provided an attachment point for Laminarian kelp (Saccharina latissima, L. solidungula, Alaria esculenta). The community associated with the kelp beds were characterized as being similar to those found in northern Atlantic waters. Large sponges and cnidarians were common, as were the chitons and mussels; barnacles (B. balanus), snails, and sipunculid polychaete worms were also common. The crab Hyas coarctatus was the dominant crustacean, along with mysids, amphipods, and hermit crabs (Pagurus trigonocheirus). The benthic communities of the coastal nearshore zone (<50 m) can be variable depending upon the salinity regime and substrate. Infaunal biomass is variable across the Arctic, ranging from 41 gC/m2 in the Beaufort Sea to over 250 gC/m2 in the Baffin Island, Lancaster Sound area (Thompson 1982). The nearshore zone in the Beaufort Sea has relatively low biomass and highly dynamic communities due to the gravelly nature of the shallow subtidal substrate. In gravelly or cobble substrate meiofauna and

barnacles dominate. In sand and sandy silts, the sediment fauna is dominated by small polychaetes (Scoloplos armiger, Spio filicornis, and Chaetozone setosa) and oligochaetes. Feder and Schamel (1976) found that species diversity, abundance and biomass increased with distance from shore, which was attributed to ice and wave action affecting stability. Nearshore coastal areas of Lancaster Sound, the high Canadian Arctic, and Greenland, infaunal communities have higher biomass, with bivalve dominated communities including Astarte borealis, A. motagui, Serripes groenlandicus, Mya truncata, Cistenides granulata, and Macoma calcarea (Thompson 1986). Similar species complexes that also included the bivalves Portlandia arctica, and Nuculana sp. are found along the Russian Arctic (Gebruk 2004). Estuarine flats and lagoons can have abundant and well developed benthic communities. Lagoon areas are often protected from fast ice and wave action, are enriched by terrestrial sources of organic matter, and have warmer water temperatures. However they may also have highly variable salinities that can limit species diversity. In lagoons along the Beaufort Sea and in the Kara Sea, infaunal diversity was noticeably lower in estuarine lagoons than the neighboring marine waters. However, abundance and biomass were equivalent or greater. As in temperate waters, the lagoons act as a rich habitat for phytoplankton, harpacticoid copepods, calanoid copepods, polychaetes (Nephtys sp., Prionospio sp., Spio sp., Terebellides sp., and Travisia sp.), Pandalus shrimp, mysids, clams (Astarte sp., Yoldia sp., Macoma sp., Portlandia sp.), a variety of amphipods (Anonyx sp., Gammarus spp.), and isopods, anadromous fishes (Arctic and Least cisco, Arctic char, salmonids) and birds (Dunton et al. 2012; Gebruk 2004). Many of the species found in the lagoon communities are similar to those found in boreal and temperate waters.

Shelf and Deepwater Communities As indicated above, the majority of the benthic habitat in the Arctic basins is fine grained sand, silt, and clay. In general, soft bottom infaunal and epifaunal communities in the Arctic are similar to those of other oceanic basin, being dominated by polychaetes, amphipods, mollusks, and echinoderms. Abundance, biomass, and species diversity in Arctic shelf communities is considered to be similar to the lower range for boreal and temperate basins. Community abundance, biomass, and diversity are variable throughout the Arctic, and are controlled by factors such as substrate type and availability of organic carbon appear to be the primary drivers for abundance and biomass (Thompson et al. 1982; Grebmeier and Cooper 2012; Piepenburg et al. 2011). In the Barents Sea, Cochrane et al. (2009) found that ice cover was inversely proportional to organic carbon and abundance. A number of studies have noted the importance of pelagic-benthic coupling in determining the benthic assemblage (Grebmeier and Cooper 2012; Carmack et al. 2006; Carmack and Wassmann 2006). Pelagic sources of organic carbon in the Arctic includes both water-column and sea-ice production. In the high Arctic, the ice algae are the primary source of carbon for the benthic communities. However, productivity in these regions is limited due to the reduced daylight and ice cover and this appears to limit abundance and biomass in the associated benthic communities. Species assemblages have also been shown to vary across the shelf from east to west, with the southern Greenland, Norwegian, and Barents Seas affected by the species in the North Atlantic. Similarly, the Siberian-Chukchi-Beaufort system is affected by Pacific species associated with the Bering Sea and Strait (Grebmeier and Cooper 2012). Beyond the shelf, species diversity, abundance and biomass decreases markedly with depth. Unlike other oceanic basins, there was no increase in diversity and biomass at the mid-depths, rather all three benthic measures decrease steadily with depth (Table 2-2; Bluhm et al. 2011). Many of the species that comprise the deep water communities are eurybenthic and are found on the outer continental shelves. Similarly, many of the dominant deep water species are similar to those of the boreal and temperate deep water communities. When considering deep water benthos, it is important to bear in mind that

data at depth in the Arctic is limited. Sampling methods commonly deployed in other ocean basins cannot be deployed in the Arctic.

Table 2-2. Abundance and Biomass for Arctic Deep-Sea Benthos (Bluhm et al. 2011). Depth Range (m) Abundance (ind. per m2) Biomass (mg C per m2) 500-1,000 2,295 436 1000-2,000 840 157 2,000 – 3,000 791 116 3,000 – 4,000 271 19 >4,000 104 10 The general taxa groups that dominate the benthic macro- and megafauna in the Arctic are similar to those of other oceanic basins, namely polychaetes, amphipods, isopods, mollusks, and echinoderms. Other epibenthic crustaceans such as crab and shrimp are also found in the Arctic but are not as common throughout the region. While polychaetes are the most abundant of the major taxa throughout the shelf, Arctic clams are perhaps a more important component in the Arctic food webs, relative to other regions, with a number of larger and important predators (e.g. walrus, bearded seal). The following section discusses each of these taxa groups.

Mollusca Bivalve mollusks are an important component of Arctic shelf communities, serving as a primary prey item for walrus and bearded seals, among other higher vertebrates. Benthic communities of the inner shelf are often defined by the dominant bivalve species. Bivalves (clams and mussels) can comprise up to 15% of the infauna in slope and plain sediments, but often dominate the biomass. In substantial portions of the East Siberian Sea-Chukchi-Beaufort and Barents-Kara-Laptev shelves, bivalves were the dominant taxa (Grebmeier and Cooper 2012; Denisenko 2007; Filatova and Zenevich 1957). The Greenland cockle, Serripes groenlandicus, is a common circumpolar bivalve found up to 100 m depth on a variety of substrates. A fairly large (up to 112 m) and long-lived clam (up to 39 years) it is a main component of the diet for walrus and Bearded seals. Macoma calcarea are also a common component in the shallower portions of the Siberian-Chukchi- Beaufort and Barents-Kara-Laptev seas (<50 m depth), as well as the fjords of northern Canada and Baffin Island. Areas with organic enrichment had higher Macoma abundance (Grebmeier and Cooper 2012; Filatova 1957). Other dominant clams in the shelf include Astarte sp., Portlandia, Mya truncata, Telina sp. and Yoldialla solidula. Deep-sea species are generally smaller and less abundant. Common deep sea species include the taxa Axinopsidae, Nucula, and Nuculanacia while other species are unique to the deep sea (e.g. Bathymodiolus spp. and Abra spp.; Gage and Tyler 1991). Clams are generally suspension or deposit feeders that are well adapted to processing particulate organic matter (POM) in the deep sea. The digestive tract in many deep-sea species is elongated with intra and extracellular digestive enzymes that allows for efficient digestion of recalcitrant forms of carbon. In addition, deep-sea clams have modified palps that sort particles before sending them to the mouth (Allen 1979). Some deep-sea species are carnivorous, with modified siphons that allow for predation on copepods and ostracods.

Polychaetes Polychaetes dominate the infaunal community on the slope, rise and abyssal plain. MacDonald et al. (2010) found dominant families in the Arctic including Cirratulidae and Paraonidae (Aricidea sp). Other species considered to have pan-oceanic distributions based are Capitella capitata, Lumbrineris minuta,

Maldanid, Oweniid, and Chaetozone complexes. There are a number of different feeding strategies used by polychaetes, including filter feeders, surface deposit feeders, subsurface-burrowing feeders, and carnivores. On the shelf and in fjords, the species assemblages change with feeding strategies. Renaud et al. (2007) found that the inner fjords and nearshore areas were typically dominated by few species and species that were highly motile or surface deposit feeders (e.g. Lumbrineris sp., Chaetozone sp.). In the mid- to outer fjords, the polychaete community was more diverse with an increase in subsurface deposit feeders. There is a strong indication for pelagic-benthic coupling in the Arctic with the distribution of benthic fauna strongly associated with patterns in the associated water column, particularly near polynyas where regionally high production in the water column is reflected in the benthic community (Piepenburg et al. 2005).

Amphipods Amphipods are common members of the benthic community, including both infaunal and epibenthic species. Amphipods are broadly distributed throughout the world’s shelf and deep sea basins. The most widely distributed species across the Arctic are Ampelisca eschrichti, Anonyx nugax, Arrhis phyllonyx, Pontoporeia femorata, Gammarus setosus, and Byblis gaimardi (Piepenburg et al. 2011; Dunton et al. 2012). Petrova and Dzhurinskiy (2012) found that Ampeliscidae were more common in the inner shelf areas, while Pontoporeiidae were more common in Bering Strait. In the Gulf of Finland, a similar trend was observed with Pontoporeiidae more abundant at the mouth of the Gulf and Ampelisca more common near the head of the Gulf. Amphipods are primarily deposit feeders or active scavengers, either free-burrowing or living in tubes. Infaunal amphipods are commonly used in toxicological evaluations of whole sediment, with established methods for testing whole sediments or spiked water samples. Lysianassid amphipods are a species rich group of epibenthic omnivorous amphipods that are key scavengers in the Arctic and deep sea waters. Many are especially adapted to scavenging with specialized mouthparts, extendable guts for food storage, and a highly motile foraging behavior. Premke (2003) has reported on food-fall scavenging activities of the Lysianassid amphipod Eurythenes gryllus in deep Arctic waters of the Norwegian Deep. However, in shallower waters, Lysianassid amphipods may have a more diverse diet. Lysianassid amphipods dominate invertebrate macrofauna in certain environments. On tidal flats, Onismus litoralis constitutes up to 95% of the macrofaunal density (Weslawski et al. 2000). Many species of Lysianassid amphipods are barotolerant. E. gryllus may be easily retrieved and decompressed from deep water with no apparent deleterious effects, as long as temperature is kept below 4 °C (Sainte-Marie 1992). Their geographic distribution and depth range is also considered to be extensive, being found throughout the world to depths up to 2,500 m above the bottom (Krapp et al. 2008, Sainte-Marie 1992, Premke 2003). Anonyx nugax is also a common benthic amphipod in the Arctic found associated with the sea ice and with abyssal communties as deep as 1700 m.

Decapod Crustaceans In general, decapod crustaceans are less common in the Arctic. There are however, several notable exceptions, particularly in the boreal-Arctic waters of the Bering Sea-Chukchi and the Barents-Greenland Seas. Crab and shrimp are the primary decapods in the Arctic. These include the shrimp, Pandalus borealis and the deep water prawns Pandalopsis dispar. In the eastern Arctic, the densest concentrations are found in the central region of the Barents Sea, Hopen Deep, Thor Iversen Bank and near the western Murman coast at depths from 200 to 350 meters. The caridean shrimp, Nematocarcinus ensifer is found from the North Sea into the Arctic. Epibenthic shrimp are primarily detritivores; however the diet is augmented with slow-moving prey such as gastropods, ostracods, and

hydrozoan polyps (Cartes 1993). In general, larval and juvenile demersal shrimp appear to occur deeper than adults, migrating to the shallower end of their distribution as they grow older. Demersal shrimp are an important food source for demersal fish, in particular Alepocepalus and Macrouridae. There is a substantial fishery for P. borealis in the Russian Arctic. The crab, Chionoecetes spp., is native to waters in Alaska, the east coast of Canada and west of Greenland, and is an invasive species in the Barents Sea. Main items in the Chionoecetes spp. diet in the southeastern Barents Sea are polychaetes, mollusks, crustaceans and echinoderms. Chionoecetes spp.in the Barents Sea were recorded in waters from 39 to 387 m depth, predominantly on muddy or sandy and muddy grounds, at temperatures from –1.6° C to 5.9° C and salinity from 34.5 to 35.1 ‰ in the near-bottom layer. In the Bering Strait and Chukchi Sea, Chionoecetes spp. has shown increased abundance (Bluhm et al. 2009; Iken et al. 2010). The Red king crab (Paralithodes camtschaticus) occurs in portions of the Barents Sea and was deliberately introduced to the Barents Sea at several locations during the 1960s and 1970s from the northern part of the Pacific (Olav and Ivanovo 1978). It has continuously spread to new areas and is now distributed from the Kluge Island to east, the Goose Bank to north, and west to Lofoten and Kvænangen to west along the Norwegian coast. The expansion of the area inhabited by red-king crabs occurred during years when water temperature in Atlantic currents was higher than normal (Pinchukov and Karsakov 2009). Several studies have revealed that the crab besides being an important fishing resource, also significantly impact the bottom ecosystem in areas of high densities of crabs (Sundet and Berenboim 2008). In the Russian waters of the Barents Sea, red-king crabs occur in areas from shallow waters to the depths below 335 m. In spring, April-May, they form spawning aggregations of individuals of both sexes, whereas in August-September, red-king crabs form separate aggregations where males aggregate in concentrations within the temperature range 4-6° С and females within 5-7° С. Red-king crabs are benthic predators (Gerasimova and Kachanov 1997; Manushin 2008), but in areas with intensive fishing, they predominantly feed on fish offal (Pinchukov and Pavlov 2002; Anisimova and Manushin 2003). The main red-king crab predators in the Barents Sea are cod and skates (Matyshkin 2003). Galatheid crabs (Munida spp) are widely distributed on bathyal bottoms in most deep ocean regions (Cartes et al. 2004). Munida tenuimana is common in the north Atlantic along the middle and lower slope from depths of 300 to 1900 m (Cartes 1993). The diet of the galatheid crabs includes polychaetes, crustaceans, and fish remains. Galatheid crabs are also found in the hydrothermal vent communities, living within the large tube worms (Martin and Haney 2005).

Echinoderms As in other oceanic basins, Ophiuroid brittle stars are among the most common megafauna occurring in Arctic shelf habitats. Dominant species include Ophiocten sericeum, Ophiura sarsi, Ophiura robusta, Ophiopleura borealis, and Ophiacantha bidentata (Piepenburg et al. 1997; Gebruk 2004; Thomson 1982 Anisimova 1989). In the Laptev Sea, populations of O. sericeum and O. sarsi were abundant (as high as 36 ind/m2) but highly variable with nearby areas devoid of brittle stars (Piepenburg et al. 1997; Sirenko et al. 2010). Similar trends were observed in shelf habitats in Greenland and Barents Sea and the outer shelf in the Siberian Sea (Bluhm et al. 2009). Most ophiuroids are motile epifaunal grazers using their flexible arms to feed on detritus, suspended organic material, small epifauna, and infaunal organisms. Ophiuroids have the ability to aggregate in areas of organic carbon deposition and have been associated in the Arctic with polynyas and marginal ice zones, where ice algae and associated detritus are deposited at higher rates (Photo 2-4). Predators

of ophiuroids include shrimp, crabs, and epibenthic feeding fish such as Zoarcidae and small Macrouridae. Other important echinoderms found on the shelf are the sea urchin, Strongylocentrotus droebachiensis, and holothoroids (sea cucumbers). Urchins can move over the seabed rapidly to form dense aggregations when responding to food, such as patches of “phytodetritus”. Urchins are a prey source for crab Return to Quick Links and larger predatory fish species.

At deeper sites, holothoroids become a dominant component of the demersal invertebrate community. Holothoroids, or sea cucumbers, are ubiquitous on the abyssal plain and relatively Photo 2-4. Dense aggregations abundant. Sea cucumbers are detritivores, ingesting sediment of Sea Stars and digesting the incorporated organic material.

Sea-Ice Realm The sea-ice realm is defined by a complex of permanent or multi-year ice that can reach thicknesses in excess of 5 m and seasonal, first-year ice that is generally <1 to 2 m in thickness (Melnikov 1997). The structure of sea-ice varies with the depth and age of the pack ice. At the ice-water interface, the sea-ice surface is uneven and porous, with brine channels that extend upwards nearly 1 m into the ice pack. Brine channels are created as the water freezes and salts are excluded from the structure of the ice. In first-year ice, brine channel density can be 50 to 300 channels per m2 and average 0.4 cm diameter (Arndt et al. 2009). The ice temperature and interstitial water salinity increases with increasing distance from the ice-water interface. Temperatures in the bottom meter of ice are relatively stable, remaining between 0 and -2°C and salinities ranging from brackish to marine (4 to 40‰; Petrich and Eiken 2010). In the middle depths of the ice pack, ice density increases, brine channels become smaller, and interstitial water salinity increases (>100 ppt). Temperatures in the mid to upper ice pack are more variable and can range from -35°C to >5°C. In older multi-year ice, the upper layers of ice are comprised of fresh water ice, with more fully developed structure and no brine channels. With the exception of some microbial and bacterial species, the majority of the flora and fauna associated with the sea ice are found on or in the bottom ~20 cm of ice. Sympagic organisms are those species that live in and on sea ice and include autochthonous species (those that spend their entire life history in the ice) and allochthonous species (those that migrate to the sea ice from the benthic or pelagic realm to spend a portion of their life cycle associated with the sea ice. The sympagic community includes ice algae, ciliates, nematodes, rotatorians, acoel turbellarians, cyclopoid and harpactacoid copepods, amphipods, and polychaetes (Melnikov 1997). These species in turn support larger pelagic and avian predators that are closely associated with the ice (e.g. Arctic and polar cod). The species composition and distribution of sympagic fauna can exhibit large spatial and inter annual variations due to the origin and history of the ice, the water depth, the physical and biological characteristics of the underlying water. Despite variation, the dominant components of the sea-ice community are similar throughout the Arctic, and include the ice algae, cyclopoid and harpacticoid copepods, sea-ice amphipods, and polar or Arctic cod. The following section will focus on these species, with reference to the associated upper trophic levels.

Ice Algae Ice algae form the base of the sea-ice food web. Although primary production by sea ice algae is generally low compared to phytoplankton, they comprise the primary source of fixed carbon to higher

trophic levels in ice covered waters (Arndt and Swadling 2006). Gradinger et al. (2010) noted that in portions of the Arctic Ocean, sea ice primary production accounts for 50% of the total annual production. In addition, the sea-ice blooms in the spring coincide with the ice melt, representing an important early source of nutrition for zooplankton (Bluhm et al. 2011). Ice algae primary production is controlled by available light and nutrients. During the Polar night, production is limited by light availability. However, increases in light during April and May initiates algal blooms. As with phytoplankton production, nutrient limitation becomes a controlling force during these blooms. The sea algal ice communities are diverse and variable throughout the Arctic, with hundreds of reported sympagic species (Sakshaug et al. 2009). While centric diatoms are a dominant form in the phytoplankton community, ice algae are dominated by pennate diatoms (Melnikov 1997; Sakshaug et al. 2010). Of 21 species observed in sea ice near Barrow, Alaska, only one centric diatom (Thalassiosira sp) was found in the sea ice. Common diatoms found in sea ice include Nitzchia spp, Navicula spp, Pinnularia, Pleurosigma, Gomphonema, and Surirella. Sea ice algae often exists as single cells within brine channels, with pennate diatoms being well suited to living in the limited space of brine channels. Along the bottom of the ice, sea ice algae may also form dense mats or long strand communities (Melosira arctica). Melnikov (1997) found long strands of the diatom Melosira arctica under multiyear ice that supports faunal communities. Ice algae also form communities in melt-ponds of the pack-ice surface. The melt-pond communities occur in the summer and autumn in brackish to marine waters that are created by melting snow and ice and marine water that penetrate upwards through channels in the ice. Melt pond communities are dominated by unicellular green algae and flagellates that are commonly found in Arctic freshwater basins at altitudes from sea level to 3000 m (Melnikov 1997). The communities shift to diatom- dominated communities as salinity in the melt ponds increases (von Quillfelt et al. 2009).

Sympagic Copepods The sympagic mesofaunal community is dominated by harpacticoid and cyclopoid copepods (Kramer 2010). These smaller copepods are generally considered to be epibenthic in nature, with feeding habits and morphology that makes them well suited to living in and under the sea-ice. Harpacticoid and cyclopoid copepods can occur in populations as high as tens of thousands per m2 in pack ice and are several orders of magnitude greater in abundance than the surrounding water column (Kramer 2010). The highest population densities generally coincide with the highest algal densities and the more moderate temperatures and salinities, within the bottom 20 cm of the ice pack (Gradinger et al. 1999; Bluhm et al. 2010). As with ice algae, sympagic copepods biomass and abundance is highly variable depending upon the ice age and location. The copepod genera Harpacticus, Halectinosoma, Tisebe and Cyclopina appear to have a circumpolar distribution (Arndt and Swadling 2006). However, the relative proportion of the dominant taxa varies with the type of ice, the region, and with season. For example, the copepod H. superfluxus and other Harpacticus species appear the be nearly absent from the interstices of perennial ice in the Arctic ocean and the northern Barents and Greenland Seas (Melnikov 1997) and are scarce underneath old ice. In contrast, in the seasonal fast ice of Frobisher Bay Canada, H. superfluxus populations can reach >380 individuals per sq. m. Another harpacticoid species, Halectinosoma sp. is typically found in multi-year ice in particular near Svalbard and northern Greenland. Both species can be found in areas where young ice and multi-year ice mix (Kern and Carey 1983). In Frobisher Bay, Grainger (1991) found two dominant copepods, Tisbe furcata and Cyclospina schneideri move to the ice in the winter months at a time when the algal production in the ice exceeds that of the sea bottom or water column. The timing of the ice-ward migration for the two species differed, with

Tisbe migrating gradually from February to April at which time, a new generation was produced. The migration of Cyclopina consisted of only young copepods moving to the ice in early winter and remaining there until April, emerging as mature adults. Despite phytoplankton blooms in the water column in early June, the two ice copepods descend to the bottom to take advantage of the organic material dropping from the melting ice and the water column (Grainger 1991). The feeding habits of harpacticoid copepods is considered to be herbivorous with little selective feeding (Grainger and Hsiao 1990; Kramer 2011), though many species will supplement their diatom-based diet with detritus during periods of low productivity (Arndt and Swadling 2006). Tisbe spp. has also been found with fish larvae and copepod eggs and copepodites (Grainger et al. 1985). Cyclopoids appear to be more omnivorous, with gut contents and lipid biomarkers showing a diet of diatoms, copepod eggs, and detritus. Cyclopoid copepods are known to use sea ice for reproduction and development. A large portion of the Cyclopina population is comprised of ovigerous females and up to three cohorts (Arndt and Swadling 2006, Kern and Carey 1983) with a generation cycle of 31 days. While the full life history of harpacticoid copepods is less well known, Arndt and Swadling (2006) infer that the ice is used for reproduction and growth, given that the eggs, nauplii and copepodite stages, as well as gravid females are found in the ice. Furthermore, harpacticoid copepods can have >10 broods per year and a generation cycle of 20 days (Tisbe furcata).

Ice Amphipods The sympagic macroinvertebrate community is dominated by ice amphipods, in particular the pan-Arctic species Gammarus wilkitzkii, Apherusa glacialis, Onismus nanseni and O. glacialis (Hop et al. 2000; Melnikov 1997; Arndt and Swadling 2006). These autochthonous amphipods reside primarily in sea ice, occupying the three dimensional structure under the ice, as well as somewhat limited use of the brine channels and structure created by the algal mats and strands. Amphipod abundance is highly variable across the Arctic. While all five of the dominant species are found in areas impacted with the perennial Arctic ice, Onismus spp. is more commonly associated with young, seasonal ice (Arndt and Swadling 2006). The amphipod G. wilkitzkii is more abundant in multiyear ice, but will move from drifting multi- year ice to first year ice. Allochthonous amphipods that are pelagic or benthic in origin are also found under the pack ice, generally taking advantage of the high spring production associated with the sympagic communities (Melnikov 1997). Planktonic amphipods may include Parathemisto spp. which can be common at the ice-water interface and may occur in swarms of several hundred individuals per m2 (Dalpadao et al. 2001). However, most allochthonous species are benthic in origin, occurring in the land fast ice, or seasonal ice forming over shallow coastal areas. Species may include Anonyx nugax, Anonyx sarsi, and G. setosus which may occur in abundance of tens per m2 (Arndt and Swadling 2006) Apherusa glacialis is an herbivorous amphipod and an important grazer of ice algae (Arndt et al. 2005). This species concentrates along ice edges and beneath more translucent new ice, where the onset of primary production takes place (Hop et al. 2000). The diet may shift towards detritus when algae become less abundant in winter. In areas with high amphipod abundance, the ice algae biomass may decrease at a rate of 30% to 60% of the standing stock per day (Arndt and Swadling 2006). Phytodetritus is a major food item for Onismus spp.; however, O nanseni is a species repeatedly collected by baited traps, scavenging on carcasses and live prey including sympagic harpacticoid and cyclopoid copepods. Gammarus wilkitzkii is primarily a predator, catching copepods, chaetognaths and other live prey, as well as amorphous organic debris, diatoms and microflagellates. Other Lysianassid amphipods that move from pelagic or benthic communities to the pack ice are typically generalists

feeding on ice algae, detritus, copepods, and fish eggs. (Arndt and Swadling 2006) These species can occur in large swarms and in turn become an important food source for Arctic and Polar cod. Sympagic amphipods have perennial life cycles and are thought to spawn once a year. Apherusa glacialis can reach 2 years in age but has a high fecundity (>500 eggs develop for 6 months in a female’s brood pouch). Offspring are released between March and August, presumably to take advantage of the spring growth of ice algae (Arndt and Swadling 2006). The life span for Onisimus spp. is 2.5 to 3.5 years (Hop et al. 2000). The reproductive cycles for the two species are offset, with O. glacialis spawning a few months earlier than O. nanseni. Both species have one brood per year and produce approximately 100 eggs over the female’s life span. G. wilkitzkii is the longest lived ice amphipod, having a 5 to 6 year life span. This species matures after two years and has one brood per year, releasing 90 to 250 eggs per year. Eggs are deposited into the females marsupium during winter and release them in April and May when primary production peaks in ice-filled waters. However, they can be flexible as the amphipods (such as G. wilkitzkii) are generalists and can release young April to September.

Pelagic Copepods The pelagic calanoid copepods common in the Arctic are commonly found under the pack ice, particularly during the spring bloom (Melnikov 1997; Arndt and Swadling 2006). While they do not appear to colonize the ice, the eggs and nauplii may be advected to the ice sheet. Calanus glacialis, C. hyperboreus, Pseudocalanus acuspes, Metridia longa, and Oithona similis perform diel vertical migrations to the ice surface at dusk (Fortier et al. 2001, 2002) to feed at the ice-water boundary. Biomass estimates for pelagic copepods are highly variable and are typically highest during the spring bloom, particularly during the ice melt (Arndt and Swadling 2006). There are some indications that during this time of both ice algae and phytoplankton blooms, calanoid copepod build up a significant portion of their lipid reserves. The ice-water interface can be an important nursery ground for Calanoid eggs and nauplii, providing food and shelter. Other omnivorous copepods, such as M. longa come to the sea-ice to feed on Calanus eggs and the small ice crustacean, as well as sympagic diatoms.

Sympagic Fish Both B. saida and A. glacialis spend a portion of their life history in close association with the sea-ice, utilizing cavities and ledges on the underside of the pack ice, as well as the edges of melting ice floes (Lonne and Guilliksen 1989; Gradinger and Bluhm 2005). The larval and juvenile life stages are commonly found individually or in small groups, with adults are seldom found in close association with the ice. In multiyear and first year ice, Lonne and Guilliksen (1989) found both one and two-year old fish living in and under the pack ice. No fish older than 2-year-olds were observed. The diet of Arctic cod in multiyear ice is comprised of a mixture of sympagic amphipods as well as pelagic copepods (Lonne and Gulliksen 1989; Melnikov 1997). In first-year ice, Lonne and Gulliksen (1989) found the Arctic cod diet dominated by calanoid copepods, however, this was likely due to the distribution and abundance of food items. Arctic cod have been observed feeding on sympagic amphipods in first year ice in other regions of the Arctic. Younger cod tended to favor harpacticoid and cyclopoid copepods, shifting to the larger prey with age (Bradstreet 1979). The amphipod, G. wilkitzkii, was seldom found in Arctic cod stomach contents. This is likely due to the large size and spiny morphology of the G. wilkitzkii.

Mammals

Ice amphipods and the more energy rich polar cod are subject to strong predation by top carnivores. The sympagic macrofauna is a major link in the transfer of energy from sympagic primary producers to the ice-associated sea birds and marine mammals. Ice seals are perennial predators under the ice. The seal diet is variable and is based on food availability. Based on stomach contents and fecal analysis from seals in the high Canadian Arctic, Arctic cod comprised the majority of the adult ringed seal (P. hispeda) diet, with small proportions (approximately 8%) of amphipods and larger pelagic copepods (Bradstreet and Cross 1982). Immature seals had a diet that was numerically dominated by ice amphipods, with approximately 3% cod. However, the cod comprised 62% of the biomass in the stomach contents. Both A. glacialis and B. saida were present in the stomach contents of young seals. When Arctic cod are less common, a variety of crustacean species dominate the stomach contents, including ice-amphipods, mysids and other under-ice fauna (Melnikov 1997). Other seals living amongst the ice include the leporine or bearded seal (E. barbatus), the harp seal (P. groenlandica), and hooded seal (C. cristata). Erignatus barbatus is primarily a benthic feeder primarily on mollusks, crustaceans, and demersal fish including B. saida and A. glacialis Return to Quick Links(Melnikov 1997; Finley and Evans 1983). Four taxa dominate the hooded and harp seal diets in Greenland: Arctic cod, capelin, the squid Gonatus fabricii and the pelagic amphipod, Parathemisto sp. (Haug et al. 2004). Based on the stomach contents and satellite tracking data, the feeding habits of these two species is more pelagic in nature and not necessarily associated with the communities under the ice.

Birds Sea birds are a primary consumer of sympagic fauna while their access is limited to areas with open water along ice edges. Important avian predators include northern fulmars, black legged kittiwakes (Rissa tridactyla), guillemots (Uria lombia and Ceppus grille), murres, thick-billed murres, Little auks (Alle alle), and gulls. Kittiwakes, Black guillemots (C. grille) and Brunnichs guillemots (U. lombia) and murres feed mainly on polar cod. Other guillemots feed on fammasur in the Canadian Arctic and Themisto spp when the water is ice free. In the Barents Sea, Little auks forage in multiyear ice mainly on A. glacialis (makes up 80% of their diet). In the Canadian and Norwegian Arctic, the diet of Little auks is primarily C. glacialis (Falk- Petersen et al. 2007).

VECs of Arctic Marine Environments The key VECS for four Arctic realms are presented in Table 2-1. In many cases, the species overlap between different realms. For example Calanoid copepods, Arctic cod, and amphipods play a key role throughout Arctic food webs. Additionally, interface habitats that contribute to the functioning and diversity of the Arctic should be further studied. These habitats include: surface microlayer, ice edges and ice margins, under-ice flora and fauna, water mass convergence zones, demersal communities and shorelines.

Seasonal Distribution Patterns of Arctic Marine Populations Determining areas of seasonal population aggregations of VECs is important to inform NEBA decision making. However, these efforts require information on life-history and presence/absence data for each VEC. Such analyses have been done for certain portions of the Arctic including the US and Canadian Beaufort. An example of such an effort is the Beaufort Regional Environmental Assessment (BREA) program in the eastern Beaufort. Seasonal movements of VEC species have been overlain with

traditional hunting grounds and other data to create VEC vulnerability profiles that indicate specific locations and time periods where the population may be sensitive to certain OSRs (Trudel 2013). As an example, data has been summarized for White whales (D. leucas) as they enter the eastern Beaufort in early June, with adults and young congregating at the mouth of the Mackenzie River delta (Figure 2-10). During July, population densities are highest close to the mouth of the river, in areas used by indigenous fisheries. In September and October, all whales leave the area. Based on the vulnerability analysis, the White whales would be most vulnerable close to the mouth of the river during July. This approach has been used in different portions of the Arctic; a pan-Arctic compilation of such data would be useful to OSR strategizing.

Table 2-1. Valuable Ecosystem Components of Arctic Communities Associated Communities Valuable Ecosystem Components Pelagic Benthic Sea-Ice Deepwater Phytoplankton ● ● Sympagic copepods Gammarus wilkitzkii ● Apherusa glacialis ● Onismus spp. ● Calanoid copepods Calanus hyperboreus ● ● ● Calanus glacialis ● ● Calanus finmarchicus ● ● Euphausiids Thysanoessa spp ● ● Hyperiid amphipods Themisto libellula ● ● Cephalopods Gonatus fabricii ● ℗ ● Pelagic Fish Arctic cod - Boreogadus saida ● ℗ ● Polar cod - Arctogadus glacialis ● ℗ ● Capelin - Mallotus villosus ● ℗ Myctophids ● ● Gonostomids ● ● Clams Serripes groenlandica ℗ ● Macoma sp. ● Benthic and Epibenthic Amphipods Ampelisca sp. ● Anonyx nugax ● ● Eurythenes gryllus ● ● Decapod crustaceans Shrimp - Pandalus borealis • • Crab - Chionoecetes spp. • Echinoderm Urchin - Strongylocentrotus droebachiensis • Epibenthic Fish Sculpin – Myoxocephalus spp. ℗ ● Eelpout – Lycodes spp. ℗ ● ● Greenland halibut - Reinhardtius sp. ℗ ● ● Mammals Ringed seal – Phoca hispeda ● ● Walrus - Odobenus rosmarus ● Narwhal – Monodon monoceros ● ● ● White whale – Delphinapterus leucas ● ● Bowhead whale – Balaena mysticetus ● Polar bear – Ursus maritimus ℗ ● Seabirds ● ● ● Integral component of the community ℗ Prey item or predator, but not an integral component of the community

Figure 2-10. Distribution of adult and young White whales (D. leucas) in the eastern Beaufort Sea. [Shaded areas represent whale densities of 1 ind (blue), 5 (green), and 50 (red); Source: Trudel 2013] Future Research Considerations

There has been a dramatic increase in data available on various aspects of marine Arctic communities over the last decade, particularly on the pan-Arctic distribution of species and trophic interactions. New studies include investigations of the trophic links within different systems (e.g. the central role of Arctic and Polar cod and Calanoid copepods in the pelagic food webs). The review of Arctic ecosystems and VECs described by the authors in this section led to suggestions of further research which can reduce remaining uncertainties. The more generic recommendations for further research compiled from this review are summarized below while recommendations that are important for improving Arctic NEBA are listed separately. 1. Continue studies on Arctic faunal groups. Some Arctic populations are now well understood in terms of natural history and toxicological profiles; however, groups of species require further examination regarding trophic roles, distributions, abundances, and ecotoxicological profiles based on annual and Interannual patterns. a. Knowledge of the interrelationships of Arctic species in areas of high productivity could benefit from further attention, especially with respect to migration and emigration through river systems, lagoons, and polynyas.

b. The distributions and abundances of benthic and bathypelagic communities of the Arctic are not well known. Boulder patch and other isolated areas of hard substrate as well as lagoon systems have proven to be important areas of increased production in the Arctic, but have received little attention. While there have been some studies evaluating the deep sea communities particularly in the Norwegian Deep, eastern Beaufort, and parts of Baffin Bay, there are substantial portions of the Arctic deep water that have not been assessed. This is a difficult area to characterize; however, recent studies in the High Canadian Arctic (Geoffroy et al. 2011, 2013, 2014; Reist and Majewski 2013) indicate that during certain portions of the year, Arctic cod can be found in large numbers in deeper waters of the Arctic. There are indications that VECs known to occupy the deep sea habitats in other oceanic basins are present in the Arctic (e.g. myctophids, deep-sea corals), however, these communities are not likely to be disrupted by near-term oil and gas activities. Deep water assessments would become important if there were a deep water release from a drilling platform. 2. Continue pan-Arctic data collation. Data from holistic efforts, such as BREA and RUSALCA could be collated and put into a GIS platform. VEC species or regions for which there is not sufficient data may require additional data collection efforts. These types of efforts generally occur as new areas are open for exploration or development. 3. Evaluate ecosystem services. Ecosystem services are the conditions and processes through which natural ecosystems and the species that comprise them sustain and fulfill human needs (Daily 1997). Marine ecosystem services include functions that support human life, such as the production of ecosystem goods (e.g. seafood) and cleansing and sequestering wastes (e.g. uptake of excess nutrients by phytoplankton). The marine ecosystem confers intangible aesthetic and cultural benefits (Kaufman and Dayton 1997; Peterson and Lubchenco 1997) to residents of the Arctic.

Priority Recommendations to Enhance NEBA Applications in the Arctic There are only a handful of studies useful to understanding the trophic interactions of emerging habitats of concern (e.g. interface habitats and deep-sea basins of the Arctic). The recommendations presented below indicate where increased knowledge of Arctic ECs and VECs would result in reducing existing uncertainties in NEBA assessments. No prioritization has been made to the list; for some of the recommendations, surrogate data may be already available. 1. Expand knowledge of Arctic ECs. Assessment of Arctic ECs should be expanded to include the communities populating interface habitats. These habitats include: sea surface microlayer, ice edges and margins, under-ice flora and fauna, water mass convergence zones, demersal communities, and shorelines. These specialized habitats and resident or transient species may contribute significantly to the overall functioning, diversity, and resilience of the Arctic. While the effects caused by individual OSR actions to key VECs living in the open water pelagic environment has been examined, repercussions of oil exposure to aggregating communities within convergent interface habitats is less well understood. a. The surface microlayer (SML). The surface microlayer refers to the uppermost surface layer(s) of the ocean. The depth of the layer(s) is defined differently by physical oceanographers, chemists and biologists based on their conceptual model developed to address their different fields of interest. Physical oceanographers and atmospheric scientists view the layer as the interface between the air and water while chemical oceanographers describe the layer based on the behavior of hydrophilic and hydrophobic

moieties of chemical compounds. Biological oceanographers define these layers based on where organisms and life stages reside or interact with the sea surface. Certain communities of plants, invertebrates and vertebrates spend all of their life history at the sea surface and these are typically referred to as neuston. The SML also acts as a nursery ground for many larval fish and invertebrate species, including larval species settling onto intertidal surfaces. This group of surface oriented species represents a community of organisms that is most closely associated with surfaced oil as the oil sheen spreads over the water’s surface. Whether the oil sheen is only a few microns or centimeters thick the organisms that contact this layer are exposed to the highest oil concentrations with the potential of activating multiple modes of toxic action. In some cases larger marine organisms can skim feed on the concentrated masses of food and contaminants (certain fish, birds, and mammals) while others swim through the layer(s) to breath. An understanding of the role of the neuston in the pelagic and intertidal food webs is needed to better characterize the impacts of surfaced, untreated oil and potential recovery rate of this vital micro-compartment. Exposure to oil at the upper sea surface layer may result in additional toxic stress via different modes of toxic action, including fouling and respiratory stress from evaporating volatile compounds. a. Ice edges and margins, polynyas and other interface communities. Polynyas have been identified as areas of enriched abundance and production during the Arctic winter. Pelagic- benthic coupling is also showing that the increased pelagic activity is mirrored in the benthic community. These different communities are typically an aggregation of species already known to be important in other portions of the Arctic. Identifying and further studying the importance of these areas is of importance for the selection of OSR alternatives. 2. Emphasize functional role of faunal groups. The list of VEC species to be included in NEBA analyses is not static for all areas of the Arctic. Emphasis will be placed on functional roles while addressing regional differences. New information regarding trophic food webs, population abundances and distribution patterns as well as toxicological profiles of VECs should be continuously expanded and updated (e.g. for ophiuroids, hard corals, jellyfish and neuston). Population size estimates of VECs that occupy interface habitats compared to bulk pelagic waters is needed to determine the relative impact of the various OSR options. 3. Increase understanding of resiliency and potential for recovery of Arctic species and populations. An evaluation of the resiliency of potentially impacted populations of VEC species within Arctic ECs is critical in determining the ultimate biological consequences of each oil spill response considered during emergency oil spill response planning. Generic metrics for resilience should be developed and scored for keystone VECs. Refer to Sections 7, 8 and 9 for further concept development (Population Effects Modeling, Ecosystem Recovery, and NEBA for Oil Spill Response Options in the Arctic, respectively).

Further Information Return to Quick Links

Authors William Gardiner and Dr. Jack Q Word (ENVIRON), Ida Breathe Øverjordet (SINTEF), Dr. Oleg Titov and Andrei Zhilin (PINRO), Dr. Thierry Baussant (IRIS)

References [Link to Chapter 2 references in Access database]