Arctic Biodiversity Assessment

486 Arctic Biodiversity Assessment

Perennial as well as seasonal sea ice make up an important habitat for Arctic marine ecosystems, where polynyas and leads make room for diverse species assemblages of birds and marine mammals. Walruses in a lead in the summer sea ice in Baffin Bay. Photo: Cherry Alexander, B&C Alexander. 487

Chapter 14 Marine Ecosystems

Lead Author Christine Michel

Contributing Authors Bodil Bluhm, Violet Ford, Vincent Gallucci, Anthony J. Gaston, Francisco J. L. Gordillo, Rolf Gradinger, Russ Hopcroft, Nina Jensen, Kaisu Mustonen, Tero Mustonen, Andrea Niemi, Torkel G. Nielsen and Hein Rune Skjoldal

Contents Summary ��488 All Eskimos (Siberian Yupik) emphasize their connection 14.1. Introduction ��488 » with the sea – boys have dreams of becoming hunters. 14.2. General characteristics of the marine Arctic ��488 The sea gives birth to our whole life … 14.3. Key forcings and structuring elements of Arctic marine Tatyana Achirgina in Novikova (2008). ecosystem biodiversity ��492 14.3.1. Water masses ��492 14.3.2. Seasonality ��493 14.3.3. Temperature ��494 14.3.4. Continental shelves ��495 14.3.5. Sea Ice ��497 14.4. Stressors and threats to Arctic marine ecosystem biodiversity ��499 14.4.1. Climate-related changes ��499 14.4.2. Exploitation of marine resources ��500 14.4.2.1. Hydrocarbons ��500 14.4.2.2. Vessel activity ��501 14.4.2.3. Commercial harvest ��503 14.4.3. Ocean acidification ��505 14.4.4. Range extensions and invasive species ��506 14.5. Status and trends in Arctic marine ecosystem biodiversity ��506 14.5.1. Historical and current status of Arctic marine ecosystem biodiversity ��506 14.5.2. Observations with respect to climate-associated changes ��508 14.5.3. Observations with respect to marine resources exploitation � 510 14.5.4. Observations with respect to range extensions ��511 14.5.5. Case studies ��513 14.5.5.1. Ecosystem regime shifts in the Bering Sea ��513 14.5.5.2. Complex ecological interactions in the Barents Sea � 514 14.5.5.3. Changes in the structure and function of the W Greenland pelagic ecosystem ��515 14.6. Conclusions and recommendations ��517 14.6.1. Vulnerabilities, adaptation and looking forward ��517 14.6.2. Knowledge gaps and challenges ��518 14.6.3. Key points and recommended actions ��518 Acknowledgements ��519 References ��519 488 Arctic Biodiversity Assessment

SUMMARY Arctic sea ice ecosystems support biodiversity at various scales ranging from unique microbial communities Arctic marine ecosystems host a vast array of over 2,000 to apex predator species such as the polar bear Ursus species of algae, tens of thousands of microbes and maritimus and walrus Odobaenus rosmarus whose ecology is over 5,000 animal species, including unique apex spe- closely associated with the sea ice environment. cies such as the polar bear Ursus maritimus and narwhal Monodon monoceros, commercially valuable fish species, Indirectly, the Arctic Ocean plays a key role in shaping large populations of migratory birds and marine mam- the global biodiversity of marine and terrestrial eco- mals, and some of the largest colonies of seabirds on the systems as it plays an essential role in the Earth climate planet. Current estimates also suggest that many species system. The Arctic Ocean also influences marine eco- are yet to be discovered. systems of the Atlantic Ocean directly, as waters and sea ice exiting the Arctic Ocean affect the physical, chemi- The marine Arctic is characterized by a wide range cal and biological characteristics of the North Atlantic. of and large variability in environmental conditions. Conversely, the Arctic Ocean receives waters from the The Arctic Ocean has the most extensive shelves of all Pacific and Atlantic Oceans, and therefore Arctic marine oceans, covering about 50% of its total area. It compris- ecosystems are influenced by global changes that influ- es diverse ecosystems such as unique millennia-old ice ence biodiversity in these oceans. shelves, multi-year sea ice, cold seeps and hot vents, and their associated communities. The Arctic is subject to rapid environmental changes. The current increase in global temperature is most rapid The Arctic is undergoing major and rapid environmental in the Arctic, with a predicted summer temperature in- changes including accelerated warming, decrease in sea crease of up to 5 °C over this century (IPCC 2007), and ice cover, increase in river runoff and precipitation, and surface water temperature anomalies as high as 5 °C re- permafrost and glacier melt. These changes together corded in 2007 (Steele et al. 2008). Arctic sea ice, a key with new opportunities for economic development cre- defining characteristic of the Arctic Ocean, is declining ate multiple stressors and pressures on Arctic marine faster than forecasted by model simulations (Fig. 1.5 in ecosystems. Meltofte et al., Chapter 1), with the potential for a summer ice-free Arctic within the next few decades (Stroeve Throughout the Arctic, ecosystem changes are already et al. 2007, Wang & Overland 2009). The effects of being observed. Changes in the distribution and abun- these and other environmental changes (e.g. changes in dance of key species, range extensions and cascading freshwater input, shoreline erosion) on Arctic marine effects on species interactions are taking place, influ- ecosystems are already documented (e.g. Wassmann et encing Arctic marine food web architecture. Unique al. 2010, Weslawski et al. 2011). These changes, together habitats such as ice shelves and multi-year ice are rapidly with increased economic interest and development in the shrinking. Arctic, put pressure on the biodiversity of Arctic marine ecosystems and on the species that inhabit them. With continued warming and sea ice decline, measures should be put in place to monitor areas of particular biological significance and uniqueness in support of 14.2. GENERAL CHARACTERISTICS OF preservation and protection measures. Moreover, the complexity and regional character of Arctic ecosystem THE MARINE ARCTIC responses to environmental changes calls for the establishment of long-term marine ecosystem observatories The Arctic Ocean is the smallest of the world’s oceans across the Arctic, in support of sustainable management (total area c. 10 million km2) and consists of a deep cen- and conservation actions. tral basin, the Arctic Basin, surrounded by continental shelves (Fig. 14.1). The Arctic Basin is further divided by the Lomonosov Ridge (maximum sill depth: 1,870 m; 14.1. INTRODUCTION Jakobsson et al. 2008) into the Eurasian and Amerasian Basins. Maximum depths (c. 5,260 m) are found near Arctic marine ecosystems are important constituents of the Gakkel Ridge, an extension of the North Atlantic global biodiversity. Arctic marine ecosystems are habi- Mid-Ocean Ridge system that divides the Eurasian Basin tats to a vast array of over 5,000 animal species and over along a line from northern Greenland to the East Sibe- 2,000 species of algae and tens of thousands of microbes rian shelf (Jakobsson et al. 2004). The Arctic Ocean has (see Josefson & Mokievsky, Chapter 8, Daniëls et al., the most extensive shelves of any ocean, covering about Chapter 9 and Lovejoy, Chapter 11). The marine Arctic 50% of its total area. The circumpolar marine Arctic also provides habitat for large populations of marine comprises the Barents Sea, Kara Sea, Laptev Sea, East mammals and birds (see Reid et al., Chapter 3 and Gant- Siberian Sea, Chukchi Sea, Beaufort Sea, Canadian Arc- er & Gaston, Chapter 4), some of which form colonies tic Archipelago and Greenland Sea. The Barents, Kara, that are among the largest seabird colonies on the planet. Laptev, East Siberian and Chukchi shelves are shallow The unique characteristics of Arctic marine ecosystems and broad (400-800 km) while the shelves from Alaska also contribute directly to global diversity. For example, to Greenland are narrow (< 200 km). Chapter 14 • Marine Ecosystems 489

180° Bathymetric and topographic tints

160°E (Meters above and below 160° Mean Sea Level) Yukon River 3 210 km per year 14 140° 0°

Kolyma 132 km3 per year 1,000 800 Mackenzie River Chukchi 120° 700 120° 264 km3 per year Borderland 600 Canada Others 500 Basin 117 km3 per year 400 300 Others

endeleev Ridge 200 3 Lena

M 209 km per year 10 525 km3 per year 0° 100 100° Alpha 50 Rigde Rigde 0 igde Yenisei R -10 618 km3 per year -25 omonosov L el kk a -50 G 80 -100

° 80° Ob -200 3 80 426 km per year °N -500 Pechora -1,000 130 km3 per year -1,500 -2,000

60° ° 60 -2,500 70 °N S. Dvina -3,000 110 km3 per year -4,000 -5,000

40 ° ° 40

20° 20°

0°

Figure 14.1. Bathymetric map of the Arctic Ocean showing general circulation and the importance of riverine inflow. (Adapted from Carmack 2000 and Jakobsson et al. 2004, 2008).

Several classifications exist for the marine Arctic, includ- size in the North Pacific (Hunt et al. 2008). As another ing eco-regions (Spalding et al. 2007) and Large Marine example, the North Water polynya region in Baffin Bay Ecosystems (LMEs) which are described as large regions supports the largest single-species aggregation of marine (200,000 km2) with distinct bathymetry, hydrography, birds anywhere on earth, namely the vast colony of little productivity and trophically-dependent populations auks Alle alle at Crimson Cliffs at Thule, N Greenland (Sherman et al. 1993). Seventeen (of 64) LMEs have been (see also Ganter & Gaston, Chapter 4). defined in the Arctic (Sherman & Hempel 2008), some of which corresponding to traditional Arctic seas/shelves The very nature of the marine environment makes it while others represent sectors of Arctic or sub-Arctic difficult to establish ecosystem boundaries, as water seas (e.g. eastern and western Bering Sea). Numerous masses are modified and displaced seasonally and shift at smaller domains within these large ecosystems have interannual to interdecadal or longer time scales, causing unique physical and biological characteristics making repositioning of fronts and associated ecological features. them ‘hotspots’ for marine productivity and biodiversity In this context, we do not define ecosystem boundaries supporting large populations of marine birds and mam- or delineate Arctic marine ecosystems as part of this mals. One example is the Pribilof Islands in the Bering chapter. We will refer to Arctic and sub-Arctic Seas/ Sea, which are renowned as an important breeding area shelf regions and, as required, direct more attention to for pinnipeds and seabirds. Despite historical depletion of ecosystem features of ecological significance such as pol- northern fur seals Callorhinus ursinus, the Pribilof Islands ynyas and marginal ice zones (MIZs). In order to provide domain supports the highest biomass of pinnipeds and a pan-Arctic perspective, we first offer a brief overview marine birds of any island or island group of comparable of characteristic features of the circumpolar Arctic seas. 490 Arctic Biodiversity Assessment

Some of the key physical forcings and structuring ele- sediment characteristics (Abramova & Tuschling 2005, ments for the biodiversity of Arctic marine ecosystems Steffens et al. 2006). are then described, followed by an overview of current and emerging dominant stressors and observations to The East Siberian Sea is the largest, broadest and shal- date with respect to impacts on ecosystem biodiversity. lowest of the Siberian shelves. The East Siberian Sea comprises two regions that are hydrographically distinct. The Kara and Laptev Seas are profoundly influenced by To the west, surface waters are influenced by direct large amounts of freshwater runoff from Siberian rivers. river input from the Lena River and relatively fresh The Kara Sea receives more than one third of the freshwater from the Laptev; to the east, surface waters are water runoff (mainly from the Ob and Yenisei Rivers) influenced by Pacific inflows and surface waters from delivered to the Arctic Ocean, contributing to the low the Arctic Basin (Pivovarov et al. 2006). The frontal salinity surface layer of the Arctic Ocean (see Fig. 14.3). zone between the two regions can vary interannually The Kara Sea is typically cold (< 0 °C) throughout the by as much as 10 degrees of longitude (Semiletov et al. year and ice-covered for most of the year. It exhibits 2005). The East Siberian Sea represents a distributional strong temporal and spatial variations in salinity due barrier for a wide variety of biota (e.g. Mironov & Dil- to fluctuations in river runoff, as well as ice formation man 2010), but is also the most poorly described of the and melt (Kulakov et al. 2006, Pivovarov et al. 2006). Russian shelves. Interannual variability in sea ice cover is associated with wind forcing (Divine et al. 2005). Differences in species The Barents and Chukchi Seas are inflow shelves (sensu richness, abundance, biomass and zonation patterns of Carmack et al. 2006) and are profoundly influenced by phytoplankton, zooplankton and benthic communities the interaction between Arctic and sub-Arctic (Atlantic are related to the salinity gradient associated with the and Pacific, respectively) waters, as well as by processes Ob and Yenisei outflows and differ between the two associated with the presence of the Marginal Ice Zone river systems (Deubel et al. 2003, Hirche et al. 2006). (MIZ) (Darby et al. 2006). The Barents Sea covers c. 1.4 million km2 extending eastwards from the Norwe- The Laptev Sea is strongly influenced by the Lena River. gian Sea to Novaya Zemlya and northwards from the The main hydrographic features include a surface mixed coasts of Norway and Russia into the Arctic Ocean and layer of c. 5-10 m in summer (Pivovarov et al. 2006), is the deepest of the Arctic shelf seas (average depth variable circulation patterns that are mainly forced by 230 m). The complex hydrography and circulation pat- winds, and an overall slow cyclonic surface layer mo- terns in the Barents Sea strongly influence its biological tion in summer (Pavlov 2001). The Laptev shelf exports production. Warm saline Atlantic waters are carried more ice to the Arctic Ocean than any other shelf, feed- by the Norwegian Atlantic Current into the Barents ing the transpolar drift with sediment-laden ice (Rigor Sea. Inshore of the Atlantic waters is the relatively fresh & Colony 1997, Eicken et al. 2000). As in the Kara Sea, Norwegian Coastal Current, whereas in the northern distribution patterns of planktonic and benthic commu- part of the Barents Sea, cold low salinity Arctic waters nities are linked to salinity gradients associated with the flow in a northeast-southwest direction, separated from river outflow, in addition to water depth, ice cover and Atlantic waters by the Polar Front (Fig. 14.2; Drinkwa-

Figure 14.2. Surface circulation of the Norwegian and Barents Seas. The red arrows represent the warm, saline Atlantic waters; the white the cold, fresher Arctic waters and 68° N the yellow the low salinity coastal waters. (Source: Drink- water 2011; see also Fig. 8.9 in Josefson & Mokievsky, Chapter 8).

64° N

60° N

0° E 10° E 20° E 30° E 40° E 50° E Chapter 14 • Marine Ecosystems 491 ter 2011, also see Loeng & Drinkwater 2007). In the over 500 km wide in some areas, whereas the western permanently ice-free, Atlantic-water-influenced south- Bering Sea Ecosystem LME has a relatively narrow shelf. western Barents Sea (i.e. where surface temperatures Ocean circulation in the Bering Sea is well described by > 0 °C), the onset of thermal stratification in spring Stabeno et al. (1999). The general cyclonic circulation initiates the development of the phytoplankton bloom. In entails the Kamchatka Current flowing southward and contrast, the northern Barents Sea, which is influenced forming the western boundary current, and the Ber- by Arctic waters, has a highly variable seasonal ice cover ing Slope Current flowing northward and forming the (both in duration and extent), and the phytoplankton eastern boundary current. Circulation in the Bering Sea bloom is typically associated with the retreat of the MIZ is strongly influenced by the Alaskan Stream entering (e.g. Sakshaug 2004). Production is significantly higher the Bering Sea through Aleutian passes. The inflow into and shows less interannual variability in the Atlantic the Bering Sea is balanced by outflow through Kam- compared with the Arctic sector of the Barents Sea (e.g. chatka Strait, so that circulation in the Bering Sea Basin Sakshaug et al. 2009, Reigstad et al. 2011). In the former, can be described as a continuation of the North Pacific annual primary production ranges between 110 and sub-Arctic gyre. Transport into the Bering Sea can vary 130 g C per m2 per year, whereas it is estimated to be by a factor of two or more, at time scales of weeks to around 55-65 g C per m2 per year in the latter (Reigstad years. Sea ice extends over the shelves in winter. In sum- et al. 2011). The Barents Sea supports highly productive mer, sea ice retreats into the Chukchi and Beaufort Seas. fisheries, one of the largest seabird concentrations in Large-scale variability is strongly influenced by atmos- the world (Anker-Nilssen et al. 2000; see also Ganter pheric patterns which, combined with sea ice conditions, & Gaston, Chapter 4) and is host to 27 migratory or influence primary productivity and fish and benthic resident marine mammal species (ICES, 2009, Reid et assemblages (Hunt et al. 2011). The southeastern Bering al., Chapter 3). Recent efforts in characterizing seabed Sea supports high numbers of demersal and pelagic fish nature and habitat also contribute invaluable knowledge and shellfish, and productive commercial fisheries. As on benthic habitat and diversity (e.g. Dolan et al. 2009; an example, Alaska pollock Gadus chalcogrammus stocks see also Josefson & Mokievsky, Chapter 8). The Barents alone yield 0.8-1.5 million metric tons a year, and are Sea is one of better understood marine ecosystems of the the most commercially valuable in total numbers, fol- Arctic (e.g. Wassmann 2011). lowed by salmon Oncorhynchus spp. Sockeye salmon O. nerka production fluctuates widely, yielding on average The Chukchi Sea receives a high inflow of Pacific waters, about 20 million fish annually (see Section 14.4.2). entering through Bering Strait. This inflow of relatively fresh, cold and nutrient-rich waters constitutes a key The Canadian Arctic Archipelago is a complex array of structuring element of marine ecosystems in this broad islands and channels, stretching from Banks Island in the (c. 400 km) and shallow (average depth of approximately west to Baffin and Ellesmere Islands in the east. The Ca- 50 m) sea. There is high interannual variability in the nadian Arctic Archipelago is a transit region for waters seasonal ice cover in the Chukchi, and highly produc- from the Arctic Ocean flowing into the Labrador Sea tive polynyas are found along the coast. Fuelled by the and the North Atlantic (McLaughlin et al. 2006 and ref- nutrient-rich inflow of Bering shelf/Anadyr water, the erences therein). These waters, mainly of Pacific origin, production in hotspots of the southern Chukchi Sea are modified by physical (e.g. mixing, freezing and sea ranks amongst the highest in the world’s oceans (e.g. ice melt) and biochemical processes during their transit. Grebmeier et al. 2006a). The Canadian Arctic Archipelago is covered by ice year- round in places, with a mix of locally-produced first- The Beaufort Sea receives water from the Alaskan year ice and multi-year pack ice from the Arctic Ocean. Coastal Current to the west, while to the east, the Ca- A number of small polynyas are also present, many of nadian Beaufort Sea is strongly influenced by freshwater, which occur together with tidally-enhanced mixing in as well as dissolved and particulate material input from the narrow channels of the archipelago (Hannah et al. the Mackenzie River. Waters of Pacific origin entering 2009). Major seabird colonies and summering areas for through Bering Strait form halocline waters on the Beau- migrant whales are concentrated in Lancaster Sound, fort shelf. Landfast sea ice, pack ice and the presence of Barrow Strait and adjacent waters. Little is known of a flaw lead polynya are typical of winter conditions in most of the Canadian Arctic Archipelago outside of the the Beaufort Sea. In summer, wind-driven upwelling Northwest Passage (from Banks Island to Baffin Bay). enhances productivity in zones of hydrodynamic singu- larities at the shelf break (Williams & Carmack 2008). The Greenland shelves are intrinsically linked to the Compared with the highly productive and strongly Pacif- network of fjords and glaciers along the Greenland ic-influenced Chukchi Sea shelf, biomass and numbers of coastline. The E Greenland shelf is influenced by the Pacific-origin species sharply decrease towards the east southward flow of polar waters carrying pack ice from (Dunton et al. 2005). the Arctic Ocean, the East Greenland Current. The W Greenland shelf is influenced by a northbound branch The Bering Sea comprises the continental shelves of of the West Greenland Current penetrating as far as Alaska and Kamchatka, also defined as separate LMEs Smith Sound (Melling et al. 2001). These ocean currents (Sherman et al. 1993), and the deep central basin be- strongly influence oceanographic conditions and pro- tween them. The eastern Bering Sea Ecosystem LME is ductivity of the Greenland shelves, as do glacier retreat 492 Arctic Biodiversity Assessment and melt impact (Heide-Jørgensen et al. 2007). The W in the Arctic Ocean. In the Barents, Norwegian and Greenland shelf is a productive shelf with important fish- Greenland Seas, species associated with warm Atlantic eries, especially for northern shrimp Pandalus borealis and waters such as deep-water shrimp, Atlantic herring Clu- Greenland halibut (or turbot) Reinhardtius hippoglossoides. pea harengus, NE Atlantic cod Gadus morhua and capelin These fisheries are essential for the economy of Green- Mallotus villosus thrive and sustain productive commercial land (Buch et al. 2004). fisheries (NMFCA 2010). The warm Atlantic Waters carry plankton species and planktonic larvae of benthic species into the Kara and Laptev Seas and into the 14.3. KEY FORCINGS AND Canadian Basin within the intermediate Atlantic layer (e.g. Sirenko 2009). In the Chukchi Sea, the distribution STRUCTURING ELEMENTS OF and diversity of zooplankton species is strongly linked ARCTIC MARINE ECOSYSTEM to water mass distribution, with different assemblages BIODIVERSITY associated with nearshore, Pacific-origin, and oceanic waters (Hopcroft et al. 2010). Pacific benthic species are Seasonal extremes in photoperiod, river runoff and ice mainly found in the Chukchi, Beaufort and the north- conditions all constitute key forcings to Arctic marine ern part of the East Siberian Seas in areas influenced by ecosystem functioning and biodiversity. In addition, Pacific waters entering the Arctic Ocean through Bering the structure, functioning and biodiversity of Arctic Strait (Dunton 1992, Sirenko 2009). The presence of si- marine ecosystems is fundamentally linked to the main licious sponge communities reported north of the Queen hydrographic features of the Arctic Ocean, namely the Elizabeth Islands in the Canadian Arctic Archipelago connection to the Pacific and Atlantic Ocean, strong (Van Wagoner et al. 1989) points to the past and present stratification and critical influence of the large continen- occurrence of Pacific-origin waters in this region. tal shelves and riverine input. Atlantic zooplankton species dominate the Arctic Ocean 14.3.1. Water masses as contemporary Pacific zooplankton species advected into the Arctic can spawn on Pacific-influenced Arctic The Arctic Ocean is connected to the Pacific and shelves (e.g. Chukchi Sea; Hopcroft et al. 2010), but do Atlantic Oceans with which it exchanges water and not successfully reproduce in the Arctic Ocean (e.g. Nel- associated physical, chemical and biological properties. son et al. 2009). Therefore, while these pelagic Pacific Relatively warm and saline (c. 34.8‰) Atlantic waters species advected into the Arctic Ocean contribute to enter the Arctic Ocean through Fram Strait and influ- the functioning of Arctic marine food webs, they only ence the biodiversity of species and ecosystems as they contribute temporarily to the biodiversity of species. In circulate cyclonically, following the bathymetry of the the benthos, Pacific-origin species permanently contrib- Arctic Ocean (see Carmack & Wassmann 2006) (Fig. ute to Arctic biodiversity in regions close to the Pacific 14.1). Pacific waters enter the Arctic Ocean through the gateway. There is no apparent zoogeographic barrier be- shallow (50 m) and narrow Bering Strait. Pacific waters tween the Canadian and Eurasian basins for zooplankton are less saline and dense than Atlantic waters and, as a (Kosobokova et al. 2011) or benthos (Bluhm et al. 2011) result, form a distinct layer on top of the Atlantic layer. except for these sub-polar expatriates. Vertical changes Pacific waters (mainly in the Anadyr Current) are also in zooplankton species diversity have been linked to the nutrient-rich, with especially high silicic acid concentra- vertical distribution of different water masses in the tions (up to 50 uM; Codispoti et al. 2005), a nutrient Eurasian and Canadian Basins with maximum zooplank- required by diatoms for the formation of their cell walls. ton species diversity in the Atlantic layer (between 300 Access to this nutrient-rich water fosters the develop- and 2,000 m) (Kosobokova & Hopcroft 2010). Overall, ment of productive diatom blooms in parts of the Arctic there appears to be a low degree of endemism on the (e.g. Tremblay et al. 2011) supporting highly productive Arctic shelves and a dominance of boreal-Arctic Atlantic food webs. species in the marine Arctic due to the constant inflow of waters from the boreal zoogeographic region (Sirenko The knowledge that currents and water mass distribu- 2009). tion influence physical conditions and the distribution of marine organisms is reflected in traditional ecological Adding to the stratification originating from the pres- knowledge. ence of Atlantic and Pacific waters, the large amount of freshwater from rivers and sea ice melt contributes to The currents are the marine animals’ access to [food]. Inuit the formation of a low salinity surface layer, the polar » also need the currents, and we are always watching the mixed layer, characterizing the Arctic Ocean (Fig. 14.3). currents for hunting. Seals come and go with the currents. There This strong stratification also plays an important role in would be no whales if there were no currents. shaping Arctic marine ecosystem biodiversity through (McDonald et al. 1997). its influence on the availability of light and nutrients for primary producers and its effects on the composition of plankton communities. This is because different func- There is inherent biodiversity associated with the pres- tional groups and species of primary producers thrive ence and circulation of Atlantic and Pacific water masses under different conditions associated with stratified/ Chapter 14 • Marine Ecosystems 493

Atlantic halocline IcePolar mixed layer Residence time ~10 years

Paci c 0 water Paci c halocline 200 Residence time ~10 years Atlantic 400 water Residence time Atlantic water Residence time 600 ~30 years ~25 years 800 Norwegian Sea and 1,000 Canada Basin Arctic deep water Eurasian Basin Greenland bottom water Eurasian Basin deep water Sea deep Depth (m) 2,000 A Residence time bottom water Residence time water ~300 years 3,000 Residence time ~75 years ~290 years 4,000 B Canada Makarov Amundsen Nansen Basin Basin Basin Basin Bering Fram Strait Alpha Ridge Lomonsov Ridge Nansen Gakkel Ridge Strait A 75° 80° 85° 90° 85° 80° B

Figure 14.3. Schematics of different water masses in the Arctic Ocean, emphasizing vertical stratification (source: AMAP 1998). well-mixed waters (Cullen et al. 2002). Diatoms, which The ecological diversity of microbial assemblages that have high nutritional requirements, thrive in environ- form the base of Arctic marine food webs (e.g. Lovejoy ments where nutrients are periodically replenished et al. 2011, Poulin et al. 2011) is essential in order to through mixing and upwelling. In contrast, small cells maintain diverse trophic pathways within Arctic ma- have high surface/volume ratios and are better adapted rine ecosystems. As a general rule, high-latitude marine to stratified environments where nutrients can quickly ecosystems that are structured around the high seasonal- become depleted. These groups have different function- ity in solar radiation sustain a high production of large alities in marine food webs, as discussed below. cells (> 5 μm) during a short period in spring/summer (e.g. Tremblay et al. 2006). These systems are consid- 14.3.2. Seasonality ered to be high export systems that can sustain abundant pelagic and/or benthic populations of fishes and marine Arctic marine ecosystems are characterized by a short mammals. In contrast, ecosystems where small cells productive period in spring-summer. Therefore many (< 5 μm) dominate are typically considered to fuel food key Arctic species have adapted to take advantage of the webs where little material is exported from the system, brief pulse in food availability after surviving the dark therefore not providing for a dependable human harvest. winter on stored energy reserves. These observations, A large part of the primary production on highly pro- together with the conspicuous presence of vast popula- ductive Arctic shelves (e.g. Bering Sea, Barents Sea and tions of marine birds and mammals, contributed to the the western part of the Greenland Sea) falls within the early view that Arctic marine ecosystems have efficient first category and supports commercial harvest, while trophic transfers and short, simple (low diversity) food the central Arctic basins currently fall within the second webs (see Horner 1985). Opposing this simplistic view, category. we now know that Arctic marine ecosystems are intri- cate and multifaceted. Arctic marine food webs range The episodic primary production in the Arctic influ- up to six trophic levels and comprise diverse trophic ences the annual cycling of nutrients as surface nutrients pathways including complex microbial food webs and re- drop near detection levels following the spring/sum- cycling pathways (e.g. Iken et al. 2005). Several thousand mer phytoplankton bloom and remain low until autumn species of microbes and protists (including bacteria, ar- (Aguilera et al. 2002), unless there is resupply, e.g. via chea and photo- and heterotrophic protists), hundreds of upwelling (Williams & Carmack 2008). Since nutrient zooplankton taxa dominated by crustaceans (Kosobok- supply is essential to sustain primary producers, such ova et al. 2011), and thousands of uni- and multicellular seasonality determines potential growth and biomass benthic taxa such as diatoms and seaweeds, foraminifera, accumulation at lower trophic levels (Tremblay & Gag- sponges, turbellarians, cnidarians, polychaetes, mollusks non 2009). The phenology of polar seaweeds (kelps) is and crustaceans contribute to the diversity of Arctic strongly tuned to the strong seasonal changes in under- marine ecosystems (Gradinger et al. 2010, Bluhm et al. water radiation and nutrient availability. Day length trig- 2011, Piepenburg et al. 2011, Poulin et al. 2011). While gers the onset of reproduction and growth particularly there appear to be comparatively fewer species that in endemic species. Arctic kelps, such as Arctic suction- channel the bulk of food to apex predators in polar than cup kelp Laminaria solidungula, are optimally adapted to in lower latitude marine food webs, the complexity and seasonal changes in nutrient concentrations and utilize diversity of the planktonic and benthic food webs that storage compounds synthesized during summer to fuel support these species are equivalent to those in temper- growth during winter (Wiencke et al. 2009). ate latitudes (Smetacek & Nicol 2005). 494 Arctic Biodiversity Assessment

14.3.3. Temperature foraging ability, reducing their hunting efficiency. This effect may account for the high abundance and diversity Notwithstanding its effect on water column stratifi- of diving birds in the Arctic and may place a southern cation, temperature is a major structuring factor for bound on their distributions (Cairns et al. 2008). biodiversity in the marine environment. Temperature impacts the life cycle of marine species, influencing While the overall cold temperature in the Arctic may their physiology and phenology (i.e. timing of events) have offered selection for cold-adapted species, low and geographic distribution (e.g. Beaugrand et al. 2002a, temperatures per se are not related to low biodiversity Edwards & Richardson 2004, Angilletta 2009). For at lower trophic levels in pelagic (Poulin et al. 2011) example, recruitment of key macroalgae and rocky bot- or in benthic communities (Kuklinski & Bader 2007). tom invertebrate species in high Arctic systems appears Although it does affect their metabolism, temperature to be much slower than in temperate systems (Dunton is typically not the primary structuring factor of plank- et al. 1982, Konar 2007). Temperature also influences tonic (Kosobokova & Hopcroft 2010) or benthic (Con- species interactions, i.e. competition and prey-predator lan et al. 2008, Bluhm et al. 2009) communities in the interactions, with consequences for biodiversity and the Arctic except nearshore, where temperature fluctuations functioning of ecosystems (e.g. Edwards & Richardson are much higher than offshore (Weslawski et al. 2010). 2004). Homoiotherms such as marine birds are generally Overall, the generally low temperatures result in low independent of direct temperature effects on their sur- metabolic rates for invertebrates, and the consequences vival. However, water temperature affects their relation- include slower growth, longer life cycles and higher ship with their prey, predators and competitors. An ex- longevity than in lower latitude systems (e.g. Bluhm et ample of such is underwater pursuit divers (auks, loons, al. 1998). The range of thermal tolerance of a species cormorants) for which warmer temperatures generally will also determine its capacity to respond and adapt to increase the swimming speed of their prey and com- changes in temperature. In this context, stenotherms petitors without commensurate increase in their own (narrow range of thermal tolerance) are likely to be

Box 14.1. Hot vents and cold seeps (mud volcanoes)

Hydrothermal vents, also called hot vents, and cold seeps are widespread features of the world’s oceans that support unique communities and contribute to the biodiversity of species and ecosystems. Hot vents have water temperatures up to 400 °C and are located on active (vol- canic) spreading plate boundaries, while cold seeps correspond to areas of seepage consisting of ‘warm’ or ‘lukewarm’ porewater, gas and mud from the seafloor. The food webs at hot vent locations are based on bacterial rather than algal growth. The chemosynthetic production of bacteria at these sites is dependent primarily on hydrogen sulphide or methane.

Hot vents are documented in the Arctic, but our current knowledge is limited, suggesting that more remains to be discovered. Hot vents are found at continental plate boundaries such as the Gakkel and Mohn Ridges (Edmonds et al. 2003) (Box 14.1 Fig. 1). It is known that the fauna of Atlantic and Pacific hot vents can have distinct communities including large-sized bacteria, clams, tubeworms and unique life forms. Communities on the Gakkel Ridge are as yet

Box 14.1 Figure 1. Known locations of hydrothermal vents and hydrocarbon seeps in the Arctic. Map created using Ocean Data View, Schlitzer 2010. (sources: Beaulieu 2010, Campbell 2006) Chapter 14 • Marine Ecosystems 495 more negatively impacted than eurytherms (wide range 14.3.4. Continental shelves of tolerance), entailing possible shifts in species dominance and the structure and functionality of ecosystems. Most of the biological production in the Arctic Ocean Of importance is the adaptation potential and range of takes place on its large continental shelves. The Arctic thermal tolerance of species. Sessile species or species shelves are highly dynamic environments where the with narrow ranges of thermal tolerance may not be able presence, formation and melt of annual sea ice influence to adapt to rapid physical and/or chemical changes in the biogeochemical cycling of organic carbon and other their environment, as opposed to planktonic or mobile elements. In addition, coastal erosion, riverine runoff organisms that may shift their distribution in relation and movement of anadromous species between freshwa- to changes (e.g. Sirenko & Gagaev 2007, Mueter et al. ters and the coastal ocean all contribute to shaping the 2009). biodiversity of Arctic marine ecosystems.

In the marine Arctic, temperature is considered to be The wide range of environmental conditions on Arctic relatively stable in central basins and in deep waters. shelves, e.g. gradients in salinity (from freshwater to However, seasonal and spatial gradients can be impor- marine environments), temperature, nutrient concentra- tant on the shelves. In addition, extremes in temperature tions, suspended matter and sediment characteristics, directly contribute to the biodiversity of Arctic ma- is fundamental to their biological diversity. The littoral rine ecosystems, with minima inside the brine channel zone, the nearshore part of the shelf where wave action system of Arctic sea ice in winter (down to –35 °C; see can move sediments, is a dynamic zone where land- Section 14.3.5) and maxima within ‘warm features’ such ocean interactions dominate. Key processes affecting as hydrothermal vents (up to 400 °C) and so-called cold littoral zone dynamics are coastal erosion, input of seeps (see Box 14.1). sediments by rivers, and sediment accretion and redis- tribution by winds, waves and currents, tidal action and ice gouging and scouring. These processes influence the distribution and structure of benthic communities via their impact on sediment grain size and availability of rocky substrates. For example, macroalgae and sessile fauna such as sponges, hydroids and many ascidians depend on rocky substrates for attachment. The distribution of seaweeds is generally restricted to rocky habitats without ice coverage for at least 4-6 weeks during the unexplored, and new species are expected to be found polar summer (Lüning 1990). Accordingly, the actual due to the isolated geographical nature of these vents northern Arctic boundary for seaweeds exceeds 80 °N, (Edmonds et al. 2003). A recent study of the Jan Mayen but excludes most of the Russian Arctic coastlines that vents on the Mohn Ridge found 180 species including a are mainly composed of soft bottoms and hence do not few new species, although the majority were common provide adequate substratum for seaweeds. to surrounding waters (Schander et al. 2010). This site did not contain high biomasses of vent-endemic fauna, The macroalgal flora in Svalbard and the White Sea (ar- similar to the Kolbeinsey vents near Iceland. However, the eas with abundant hard bottom) is generally composed of communities at these two vent locations shared almost species also found in other regions of the North Atlantic, no fauna in common (Schander et al. 2010), highlighting some boreal species at the limit of the northern distribu- differences in regional biodiversity. tion range (e.g. forest kelp Laminaria hyperborea; Müller et al. 2009), and very few species with a strong distribu- Cold seeps are widely distributed in the Arctic, occur- tional center in the Arctic (e.g. Arctic suction-cup kelp ring on the Beaufort shelf, Barents Sea slope, Norwegian and the red algae Devaleraea ramentacea). On the Alaskan shelf and Arctic mid-ocean ridge (Box 14.1 Fig. 1). Many Beaufort Sea shelf, macroalgae are restricted to small sites (e.g. the Haakon Mosby Mud Volcano, Barents Sea) areas where hard substrata protected from ice scour are represent hotspots of biodiversity in deep waters (Van- available (Wulff et al. 2009 and references therein). Ice reusel et al. 2009), with the diversity of organisms varying scouring in nearshore areas can also regularly eradicate widely between sub-habitats such as microbial mats or benthic communities, resulting in a mosaic of succes- the outer rim area (Van Gaever et al. 2006). Fishes such as sion stages in those areas (Conlan & Kvitek 2005). This scalebelly eelpout Lycodes squamiventer and several spe- emphasizes the role of sea ice in structuring benthic eco- cies of skates are known to utilize the rich resources of systems (see also next Section). On the shelves, the main deep-water cool seeps. Mud volcanoes in shallower wa- sessile primary producers are seaweeds and, to a lesser ter (e.g. Beaufort shelf) can also create habitat for distinct extent, benthic diatoms. To date, a total of more than nearshore benthic communities (Conlan et al. 2008). 200 seaweed species have been recorded for the Arctic (Wilce 1994, Archambault et al. 2010, Mathieson et al. 2010, Daniëls et al., Chapter 9). In some areas, perennial seaweeds are abundant and serve as food and habitat to a diversity of invertebrate and fish species (Dunton et al. 1982, Mathieson et al. 2010). Therefore, changes in this 496 Arctic Biodiversity Assessment

Box 14.2. The role of polynyas for Arctic seabirds and mammals

Polynyas are recurrent areas of open water amidst ice-cover. nent polynyas occasionally causes entrapments (Nerini et al. They occur throughout the Arctic as flaw leads that form 1984, Finley 2001) sometimes involving hundreds of whales along the edge of fast ice areas (Box 14.2 Fig. 1), or as latent (Harwood & Smith 2002). This is a well known phenomenon (driven by wind forcing) or sensible (driven by the upwelling (named sassat in Inuit) re-occurring at certain sites in Arctic of warmer water) heat polynyas (see Williams et al. 2007) and Canada and Greenland, where local hunters may take advan- play an important role in the productivity and biodiversity of tage of the opportunity to secure large amounts of narwhal Arctic marine ecosystems. or beluga meat (see Siegstad & Heide-Jørgensen 1994).

Polynyas of all kinds may be sites of enhanced or early season In regions of very high tidal currents, such as those produced productivity, making them important biological hotspots in narrow inlets, small tidal polynyas remain open through- (e.g. Bursa 1963, Hirche et al. 1991, Stirling 1997). In summer, out the winter, providing refuges when shore-leads close the region of the North Water Polynya in Baffin Bay supports temporarily. Such predictable areas serve to concentrate some of the largest concentrations of seabirds anywhere a wide variety of marine birds, and sometimes whales and in the Arctic (Stirling 1980, 1997), dominated by little auks seals. The resulting aggregations of potential prey attract ice- Alle alle which breed in the tens of millions in N Greenland based predators (polar bears and Arctic foxes Vulpes lagopus) (Kampp et al. 2000). Little auks time their arrival to coincide and raptors such as gyrfalcons Falco rusticolus and snowy with the availability of copepods Calanus spp., their primary owls Bubo scandiaca (Brown & Nettleship 1981, Kingsley et prey in May-July. Thus, the timing and location of little auks al. 1985, Stirling 1997, Therrien et al. 2011). Numerous small in the region is determined by primary production and the polynyas of this sort occur in the Belcher Islands (Sanikiluaq), consequent upward migration of copepods, rather than by where they are essential to the year-round existence of a the availability of open water itself (Karnovsky & Hunt 2002). large population of common eiders (Freeman 1970). The common eiders forage in shifting flaw leads while retreat- Large recurrent polynyas provide conditions for a diverse ing to the permanent tidal polynyas over night (Gilchrist & array of birds to remain for the winter, especially common Roberston 2000, Gilchrist et al. 2006). Similarly, the entire eiders Somateria mollissima, and to a lesser extent long- world population of spectacled eiders Somateria fischeri tailed ducks Clangula hyemalis and king eiders Somateria winters in leads and polynyas south of St. Lawrence Island spectabilis (Gilchrist & Robertson 2000), as well as ice-associ- in the eastern Bering Sea (Petersen et al. 1999), an area of ated seals and whales (Kingsley et al. 1985, Heide-Jørgensen strong benthic-pelagic coupling that supports a high density & Laidre 2004, Moore & Laidre 2006). The overwintering of of bivalve prey for the eiders (Lovvorn et al. 2003, Grebmeier ice-associated whales within mobile pack ice and imperma- et al. 2006a). (See also Ganter & Gaston, Chapter 4.)

community are expected to influence various trophic nus alpinus, brook trout Salvelinus fontinalis, brown trout levels in marine Arctic ecosystems. Salmo trutta and whitefish Coregonus spp.). Anadromous fish species such as Arctic char are distributed through- The immense freshwater inflow into the Arctic Ocean out the circumpolar Arctic (see Fig. 6.3 in Christiansen not only produces a permanent halocline throughout & Reist, Chapter 6). Many sub-species exist, and their the Arctic (Fig. 14.1 and 14.2), but also results in large biodiversity is still poorly understood. Seaward migra- horizontal salinity gradients in nearshore waters. These tion in Arctic anadromous fishes, although facultative, gradients are reflected in the zonation of biological com- appears to be advantageous as anadromous species take munities, ranging from freshwater near river mouths advantage of marine coastal production. to brackish water and full marine species assemblages. These varying conditions on Arctic shelves contribute Arctic shelves also serve as feeding areas and migration to increasing the overall biodiversity of Arctic marine corridors for resident or migrant whales in the Arctic. ecosystems (e.g. Deubel et al. 2003, Steffens et al. 2006). The three endemic species of Arctic cetaceans, the narwhal Monodon monoceros, beluga Delphinapterus leucas Linking freshwater systems to the sea, Arctic shelves and bowhead whale Balaena mysticetus, exploit different also host a diversity of anadromous fishes, i.e. fishes that habitats (Heide-Jørgensen 2009, O’Corry-Crowe 2009, use freshwater environments for spawning and early life Rugh & Shelden 2009). Narwhals primarily occupy the history (and in the Arctic overwintering) and estuaries/ Atlantic sector of the Arctic, north of 60° N latitude. coastal environments for feeding and rearing. Of the They overwinter in dense pack-ice habitats along the 39 species of anadromous fishes that are found in the continental slope where they feed intensively from No- Arctic and sub-Arctic (see Christiansen & Reist, Chapter vember to March, and spend the summer months in ice- 6), many are regarded as being of high importance for free shallow bays and fjords. Belugas occupy estuaries, harvest by local communities (e.g. Arctic char Salveli- continental shelves/slopes, and deep basins in conditions Chapter 14 • Marine Ecosystems 497

Box 14.2 Figure 1. Circumpolar map of known polynyas. Note that some polynyas no longer exist in the form known from their recent history. (Source: Barber & Masson 2007.)

ranging from dense annual pack ice to open water. Some in combination with snow cover decreases light avail- belugas (e.g. along the Alaska coast, in the Canadian ability for primary producers. Therefore, snow cover high Arctic and Hudson Bay) undertake long migra- and sea ice melt/break-up appear to control the timing tions between summer and wintering sites, while others of the ice-associated (i.e. ice algae) and pelagic (i.e. phy- remain in the same region year-round (e.g. Lydersen et toplankton) blooms by acting on the availability of light al. 2001, Richard et al. 2001). Bowhead whales migrate (e.g. Michel et al. 2006, Lavoie et al. 2009). from sub-Arctic seas in winter into the high Arctic in summer. Bowheads often feed in polynyas (see Box 14.2) Sea ice is also an ecosystem in itself, therefore contrib- or areas covered with loose sea ice in spring or in open uting directly to the biodiversity of the marine Arctic. water areas in late summer and autumn when sea ice has The unique physical and chemical conditions in sea retreated offshore (Moore et al. 2010). A variety of other ice, and their wide range, create a variety of habitats baleen whales such as the gray whale Eschrichtius robustus for a diversity of microbial and meiofaunal communi- together with a few toothed whales (e.g. the killer whale ties. For example, sea ice salinity can range from nearly Orcinus orca) also migrate into Arctic waters during sum- zero (freshwater) in multi-year ice to > 200‰ in sea mer, but the presence of sea ice represents a distribu- ice brine channels and pockets that range from less tional barrier to these animals (Higdon et al. 2011). (See than 1 micro m to 1.2 mm in size (Krembs et al. 2000). also Reid et al., Chapter 3.) Temperature and light conditions also vary widely, spa- tially and seasonally. The sea ice ecosystem harbors an 14.3.5. Sea Ice abundance and diversity of microbes including viruses, archaea and bacteria of the groups Proteobacteria and In the Arctic, sea ice is a major structuring element of Cytophaga-Flavobacterium-Bacteriodes (CFB) (Deming marine ecosystems. The presence of sea ice impedes sur- 2010, Lovejoy et al. 2011, Lovejoy, Chapter 11). Sea-ice face mixing, influences freshwater and heat fluxes, and bacterial communities comprise species of Marinobacter, 498 Arctic Biodiversity Assessment

Shewanella and Pseudomonas, with apparent potential to amphipods are also a main food resource for the polar degrade hydrocarbons (Gerdes et al. 2005). Thousands cod Boreogadus saida and ice cod Arctogadus glacialis (Brad- of protist species are also found in sea ice (Ró ˙z a ´n ska et al. street & Cross 1982, Christiansen et al. 2012), which are 2009, Poulin et al. 2011), but there is still much debate the only ice-associated marine fish species in the Arctic. with respect to the endemic character of some of these Polar cod occurs in variable-sized schools ranging from protist species. The colonial diatom, Nitzschia frigida, is small groups to several million fishes across the Arctic considered a pivotal species of land-fast ice across the (Andriashev 1964, Craig et al. 1984). Both fish spe- Arctic as it is the most frequent, most abundant and cies are important food items for higher trophic levels most consistently observed species in first-year sea ice (Bluhm & Gradinger 2008), including ringed seals Pusa (Ró ˙z a ´n ska et al. 2009). Protist species living in sea ice hispida, narwhals and belugas (e.g. Labansen et al. 2007). are adapted to the extreme conditions in their environ- Arctic sea birds (fulmars, murres, guillemots, kittiwakes ment. Productive cryo-tolerant microbial communities etc.) also feed on polar cod throughout the Arctic (e.g. are found on ice shelves (see Box 14.3; Mueller et al. Lønne & Gabrielsen 1992, Hobson 1993, Weslawski et 2005) and ice algal species Chlamydomonas sp. can grow al. 2007, Karnovsky et al. 2008). at –5 °C and at salinities ranging from 2.5 to 100‰ (Eddie et al. 2008). A diverse community of multi-cellu- Sea ice also serves as an essential structuring element for lar organisms also lives within the ice (often referred to habitat used by seals, polar bears and cetaceans (Reid et as ice meiofauna), including over 20 species of crustaceas al., Chapter 3). All seven seal species found in the Arctic (mainly Harpacticoida), nematodes, Acoela, Rotifera are closely associated with the ice ecosystem, and use and Cnidaria (Gradinger 2002, Bluhm et al. 2010). In the ice habitat either for birthing, feeding or as a resting addition, meroplanktonic larvae and juveniles stages of platform (e.g. Laidre et al. 2008, Kovacs et al. 2011a). benthic Polychaeta and Gastropoda inhabit the ice for For example, ringed seals, which are the most abundant periods of a few weeks to months (Gradinger et al. 2010, Arctic seals, use the sea ice for birth, rearing and molt. Josefson & Mokievsky, Chapter 8). Grazing by sea ice Ringed seals have a circumpolar Arctic distribution and meiofauna does not appear to limit the accumulation of constitute a major food item for polar bears (Thiemann ice algal biomass (Michel et al. 2002). et al. 2008) and humans. Polar bears are closely associated with the sea ice as they use it extensively for foraging Recently, the key role of ice algae in Arctic pelagic and and for transportation to/from terrestrial denning areas, benthic food webs has been clearly demonstrated using often found along slopes near shorelines where snow- biomarkers (McMahon et al. 2006, Søreide et al. 2006, drifts accumulate sufficient snow (Stirling 2009). 2008, Tamelander et al. 2008). For example, Søreide et al. (2010) showed that ice algae are essential for the Ice shelves also constitute unique Arctic ecosystems. development and survival of Calanus glacialis, a key They directly impact ecosystem biodiversity, as they zooplankton species consumed by fishes, seabirds, seals create unique habitats for diverse microbial communities and bowhead whales across the Arctic. Sea-ice associated forming thick mats (Vincent et al. 2000, 2004). These

Box 14.3. Extremophiles in the marine Arctic

The lowest temperature at which active life has been found temperatures but also high salinity, and can be faced with on Earth is about –20 °C, with records of bacteria living in other challenges such as nutrient availability within these permafrost and sea ice (D’Amico et al. 2006). Cold-adapted micro-habitats. organisms are called psychrophiles. Psychrophilic species can grow at temperatures < 0 °C, have an optimum growth Extremophile adaptations are primarily associated with cel- temperature < 15 °C and cannot grow above 20 °C (Thomas lular proteins (e.g. enzymes of high specific activity; D’Amico & Dieckmann 2002). Psychrophilic organisms represent a et al. 2006), as they control the balance between cellular diverse group of bacteria, archaea, yeasts, fungi and algae substrates and production, nutrient fluxes, removal of waste and play a key role in nutrient cycling and the transformation products and the assembly of cellular components including of organic matter. DNA. The production of polyunsaturated fatty acids as well as other changes in the composition of lipid membranes is Within Arctic sea ice, extremophile habitat consists of also critical for maintaining membrane fluidity and proper channels or pockets that contain liquid brine. These liquid functioning of the cells (Thomas & Dieckmann 2002). Outside habitats within the sea ice can persist at temperatures as low the cell, cryoprotectant materials such as exopolymers have as –35 °C (Deming 2002). The liquid inclusions are reduced in multiple roles that aid the survival of bacterial and algal extre- size and connectivity as ice temperatures decrease, and the mophiles in the sea ice (Krembs & Deming 2008). There is still salinity of the brine can exceed 200‰, compared with val- much to learn about the biodiversity of these extreme habi- ues of about 32‰ in surface waters of the Arctic. Therefore, tats and extremophiles as well as the mechanisms they use to sea-ice extremophiles are adapted to survive not only cold survive within the sea ice and extremely cold environments. Chapter 14 • Marine Ecosystems 499 cryotolerant microbial mats are hypothesized to have and 1930s, the North Atlantic experienced a dramatic provided refugia for the survival, growth and evolution increase in atmospheric and ocean temperatures resulting of a variety of organisms during periods of extensive ice in marine ecosystem changes (reviewed by Drinkwater cover such as the Proterozoic glaciations (Vincent et al. 2009) including a northward range expansion of boreal 2000). Calving ice shelves and icebergs also impact the fish species (Perry et al. 2005), phytoplankton species biodiversity of ecosystems through which the ice travels (e.g. Smyth et al. 2004) and benthic invertebrates into the (see Box 14.5, Section 14.5.2). Barents Sea (Blacker 1957).

The rapid decrease (13% per decade) in the minimum 14.4. STRESSORS AND THREATS TO (summer) Arctic sea ice extent over the past three decades (Comiso et al. 2008) and accelerated melt compared ARCTIC MARINE ECOSYSTEM with model predictions (Barber et al. 2009, Wang & BIODIVERSITY Overland 2009; see Fig. 1.5 in Meltofte et al., Chapter 1) prompts concerns that the Arctic Ocean could be The Arctic is undergoing major and rapid environmental virtually ice free in summer by 2040 (Meier et al. 2011). changes including accelerated warming (Zhang 2005, Multi-year ice, so far considered a permanent feature of Steele et al. 2008), decrease in sea ice cover extent central Arctic basins and typically representing about (Stroeve et al. 2007, Comiso et al. 2008) and duration half of the Arctic sea ice coverage, has declined rapidly (Stroeve et al. 2006), increase in runoff and precipitation over the last decade to make up less than 15% of sum- (Dyurgerov et al. 2010), and permafrost and glacier melt mer sea ice extent in 2010 (National Snow and Ice Data (IPCC 2007). The rapidly diminishing Arctic sea ice Center 2010). The total multi-year ice volume in winter cover, in particular the decline in thick multi-year ice, experienced a net loss of > 40% in the four years fol- has unlocked tremendous opportunities for economic lowing 2005 (Kwok et al. 2009). Arctic climate patterns development through the exploitation of natural resourc- observed over the last decade are distinctly different es that were previously unreachable, new transportation from those in the past century, resulting in enhanced sea and shipping routes and increased tourism. ice loss (Overland et al. 2008).

The main currently anticipated threats to biodiversity The rapid warming taking place in the Arctic, exempli- are both direct, such as the change in land use and oil fied by the rise in seawater temperatures of up to 4 °C spills, and indirect, such as the ability of key organisms expected in the Atlantic sector of the Arctic Ocean to acclimate to new conditions of temperature, CO2, (Müller et al. 2009), is expected to have direct and indi- and ice, freshwater and seawater dynamics. The im- rect impacts on the biodiversity of marine ecosystems. It mense changes in climatic forcing of the Arctic over has been proposed that critical temperature thresholds relatively short evolutionary time scales suggest that its exist in marine ecosystems, leading to abrupt ecosys- ecosystems are capable of reorganization, but the range tems shifts rather than gradual changes (Beaugrand et al. and survival of individual species is less certain (Car- 2008). One such example is the shift from a boreal to a mack & Wassmann 2006). temperate ecosystem, associated with a surface temperature increase of just over 1 °C in the North Sea over the 14.4.1. Climate-related changes last 40 years (Beaugrand et al. 2008). Warming in the North Atlantic and adjacent seas has also been linked to Fluctuations in climate are documented from geological large-scale biogeographic changes in the biodiversity of records and ice cores. Sedimentary records from Arctic calanoid copepods over the period 1960-1999 (Beau- continental margins reveal centennial- to millenial-scale grand et al. 2009). fluctuations in ice drift patterns, the position of the marginal ice zone and temperature and salinity in surface Temperature modulates the biodiversity of marine ecosys- and subsurface water masses (Darby et al. 2006). Nota- tems through its combined effects on species phenology, bly, over the past thousand years, alternate warming and interactions and geographic distribution. For example, cooling of the North Atlantic occurred during the Medi- temperature requirements for growth, reproduction and eval Warm Period (9th to mid-15th century) followed by survival are the major factors responsible for determin- the Little Ice Age (mid-16th to early 20th century) (Darby ing geographical distribution boundaries of macroalgae. et al. 2006). Evidence for impacts of past climate fluctua- The eurythermal character of some Arctic species should tions on Arctic marine biota are numerous. For example, benefit these species under increasing water temperatures. oral as well as written records from the last centuries There are many species in the Arctic that also grow in and archaeological remains of Inuit hunting communi- cold-temperate regions. However, it seems that tem- ties from the last 4-5 thousand years provide evidence for perature tolerance for survival is, in contrast to tempera- large distributional and numerical fluxes of sea mammals ture requirements for growth and reproduction, a very and sea birds in response to climatic fluctuations (Vibe conservative trait (e.g. Hirche et al. 1997), which probably 1967). Another example is the boreal blue mussel Mytilus only changes over long evolutionary periods. Hence, the edulis that was established as far north as Svalbard during pace of species adaptation to the rapidly warming Arctic early postglacial periods, after which the species disap- may well lag behind that needed for survival. peared until this decade (Berge et al. 2005). In the 1920s 500 Arctic Biodiversity Assessment

Warming combined with increased precipitation has 14.4.2. Exploitation of marine resources caused an increase in freshwater discharge into the Arctic Ocean (Dyurgerov et al. 2010). Increased river The marine Arctic offers a wealth of natural resources, outflow is expected to cause larger marine areas to be especially fossil fuels and fisheries whose exploitation, impacted by estuarine circulation patterns leading to together with climate change, is resulting in increasing a displacement of marine taxa, with potential loss of pressures on Arctic marine ecosystems. diversity (Bluhm & Gradinger 2008). Inputs of inorganic sediments and organic carbon to the Arctic Ocean by 14.4.2.1. Hydrocarbons rivers and eroding coast lines may have changed as well, but analyses of available time series do not show identifi- Extensive oil and gas activity has occurred in the Arc- able long-term trends (Holmes et al. 2002). tic, primarily land-based, with Russia extracting 80% of the oil and 99% of the gas to date (AMAP 2008). In addition to direct impacts of changing sea ice condi- Furthermore, the Arctic still contains large petroleum tions (i.e. sea ice structure, extent and distribution) hydrocarbon reserves and potentially holds one fifth of on Arctic ecosystems, indirect impacts of the warm- the world’s yet undiscovered resources, according to the ing Arctic include increased erosion and changes in the US Geological Survey (USGS 2008) (Fig. 14.4). While timing of sea ice melt and freeze-up. The melt period much of the currently known Arctic oil and gas reserves was, on average, 13 days earlier in the 2000s compared are in Russia (75% of oil and 90% of gas; AMAP 2008), with the 1980s (Stroeve et al. 2006, 2007). Freeze-up more than half of the estimated undiscovered Arctic is also delayed, up to seven days per decade later for the oil reserves are in Alaska (offshore and onshore), the Chukchi/Beaufort and Laptev/East Siberian Seas, mak- Amerasian Basin (offshore north of the Beaufort Sea) ing the open water period 20 days longer (Markus et al. and in W and E Greenland (offshore). More than 70% 2009). Later freeze-up and earlier melt in coastal areas of the Arctic undiscovered natural gas is estimated to is extensively reported in traditional ecological knowl- be located in the W Siberian Basin (Yamal Peninsula edge. Peter Elachik, from Kotlik, Alaska, reports large and offshore in the Kara Sea), the E Barents Basin and in changes in the time when safe travel can take place on Alaska (offshore and onshore) (AMSA 2009). Associated the ice at the mouth of the Yukon River. with future exploration and development, each of these regions would require vastly expanded Arctic marine operations, and several regions such as offshore Green- So there’s a lot of difference between 1945 and 2005. land would require fully developed Arctic marine trans- » Big change. port systems to carry hydrocarbons to global markets. (Peter Elachik, Kotlik; in Fienup-Riordan & Rearden 2010). In this context, regions of high interest for economic development face cumulative environmental pressure from anthropogenic activities such as hydrocarbon exploita- Warming, changes in stratification, diminished ice tion locally, together with global changes associated with cover, delayed ice formation and advanced break-up, and climatic and oceanographic trends. a longer open water period have tremendous impact on individual species (e.g. polar bear; see Reid et al., Chap- Oil spills are considered to be the largest environmental ter 3) and on the characteristics of ecosystem production threat from oil and gas activities in the Arctic marine and its channeling to higher trophic levels (e.g. Grebmei- environment, but habitat fragmentation and disturbances er 2012). For example, earlier ice melt might limit ice also constitute pressures to various ecosystem com- algal production and its contribution to Arctic primary ponents (AMSA 2009). For example, noise associated productivity, but cause earlier and increased phytoplank- with hydrocarbon activities can be deleterious to marine ton productivity (Arrigo & van Dijken 2011). Earlier ice mammals. Increased noise can disrupt their behavior melt might also favor a shift from a benthic to pelagic or prevent detection of other sounds that are important dominated food web on the shelves, as suggested for to the marine mammals (e.g. Richardson et al. 1995, the Bering and Chukchi Seas (Grebmeier et al. 2006b, Nowacek et al. 2007). The accidental release of oil into Bluhm & Gradinger 2008). Changes in the timing of the the Arctic marine environment threatens all trophic ice algal and phytoplankton bloom may have important levels (e.g. Cross et al. 1987, Muir et al. 1999). Most consequences for trophic transfers in Arctic food webs obvious to the public are effects on birds and mammals, (Michel et al. 2006, Leu et al. 2011). Long-term studies by compromising their feathers and fur, resulting in hy- in W Greenland provide evidence for such effects (see pothermia and potential mortality. Metabolic effects are Section 14.5.3). The duration of the open water period also documented for invertebrates, birds and mammals is also critical to the distribution of marine birds and (e.g. Suchanek 1993, Muir et al. 1999). Arctic seabirds mammals in ice-covered regions such as the Canadian and marine mammals are particularly susceptible to oil Arctic Archipelago. Examples of observed changes and spills because they congregate in large numbers to breed, trends in relation to climate-associated changes are dis- nest and rear young at certain times and locations each cussed in Section 14.5.2. year. Moreover, the logistical challenges of cleaning up an oil spill in the Arctic could lead to oil persistence in affected areas, consequently causing uptake of oil in marine and coastal food webs. Chapter 14 • Marine Ecosystems 501

Figure 14.4. Circumpolar distribution and probability of potential petroleum reserves in the North (source: US Geological Survey 2011).

14.4.2.2. Vessel activity Cargo traffic for community re-supply is expected to ex- pand in the near future, mainly due to economic devel- Most information presented here is derived from the opment and population increases in Arctic communities, recent Arctic Marine Shipping Assessment (AMSA but also due to the shortened seasonal use of ice-roads. 2009). Current vessel activities in the Arctic can be cat- Cruise ships to the Arctic have already significantly egorized into four main groups: community re-supply, increased in numbers over the past few years. Over 2.5 cargo ships, fishing activity and tourism. The majority million cruise ship passengers traveled to the Arctic in of vessel activity, and consequently ship accidents, takes 2007, a number more than twice the estimate for 2004. place along the coast (Fig. 14.5). Therefore continental In Greenland alone, the number of cruise ships has more shelves, which are areas of high biodiversity and produc- than doubled from 2003 to 2008 (Fig. 14.6b). Similar tion and large aggregations of Arctic marine fauna, are increases can be expected in some other coastal regions most susceptible to impacts from ship traffic. of the circumpolar Arctic, where there is adequate access to major ports. The decrease in multi-year ice and longer open water season opens new shipping routes and opportunities for On a global scale, the total number of vessels navigating tourism, while offshore leases for oil and gas explora- in the Arctic represents a small proportion of the world’s tion (e.g. in the Beaufort, Chukchi and Barents Seas) are fleet. However, impacts on Arctic marine ecosystems expected to stimulate coastal-offshore marine activity can still be significant due to their unique characteristics over the next decade(s). Increased marine traffic is now and to the limited infrastructure and variable emergency a reality in the Arctic. The Northwest Passage (Canadian response preparedness in remote Arctic locations. Arctic Archipelago) has seen increased vessel transits over the past three decades, and especially in the past A significant threat from ships to the Arctic marine five years (Fig. 14.6a). environment is considered to be the release of fuel and/ or oil, which is routinely discharged into the marine en- A potentially ice-free Arctic Ocean in summer in a few vironment through tank washings, deck runoff and bilge decades also opens opportunities for increasing scien- water discharges. The introduction of alien and possibly tific, exploration and tourism vessel activity in central invasive species via ballast water discharge can also be Arctic basins. a serious threat to marine ecosystem biodiversity (see Lassuy & Lewis, Chapter 16). Impacts of ballast water 502 Arctic Biodiversity Assessment

Figure 14.5. Locations of sub-Arctic and Arctic shipping accidents and incident causes, 1995-2004 (source: AMSA 2009).

80 400 Figure 14.6. Number of a) b) ships a) transiting through the Northwest Passage (five year intervals, from 1975 to 2010), 60 300 and b) landing in Greenland (cruise ships only, from 2003 to 2008. (Sources: AMSA 2009 updated with 2010 data and 40 200 NORDREG 2009; se also Fig. 16.1 in Lassuy & Lewis, Chapter 16). Number of transits 20 100 Cruise ship arrivals in Greenland

0 0 1975- 1980- 1985- 1990- 1995- 2000- 2005- 2003 2004 2005 2006 2007 2008 1980 1985 1990 1995 2000 2005 2010 Chapter 14 • Marine Ecosystems 503 introductions have been reported to modify food webs ter 18). Similarly, numbers of murres in Novaya Zemlya and trophic interactions in other marine environments remain considerably depressed following harvesting of (Molnar et al. 2008). Other potential impacts include eggs in the 1940s (Bakken & Pokrovskaya 2000). Many the release of grey water sewage, accidental strikes of local reductions probably took place as a result of inci- marine fauna and the introduction of noise or other dental harvest during whaling and sealing expeditions, acoustics (e.g. sonar). but these are unknown.

Of concern is that the presence of ships and their noise The impact of historical harvest of marine mammals may disrupt habitat and migratory patterns of marine and seabirds on the current architecture of Arctic mammals (Tyack 2008). There is a broad geographi- marine ecosystems is unknown. However, it is certain cal correspondence between the routes used by marine that the removal of the large biomass of targeted spe- mammals (bowhead, beluga, narwhal, walrus) on their cies or functional groups contributed to shape the flow spring migration to summer feeding grounds in the of energy and materials and trophic interactions within Arctic and Arctic shipping routes, notably through the present-day Arctic marine food webs. This is discussed Bering Strait, Lancaster Sound and the Kara Gate. At in Section 14.5.1. present, most shipping movements take place after the mammals have migrated through these choke-points. Today, commercial fisheries are found in the produc- With less sea ice there may be a longer season of navi- tive Barents, Bering, Norwegian and Greenland Seas gation with the potential for more conflicts between and around Iceland, supporting high catches of vari- migratory species and ships. Key sensitivities of Arctic ous fish and invertebrate species (e.g. capelin, pollock, marine ecosystems to vessel activities include the pres- halibut, Atlantic cod, shrimps and crabs). Time-series ence and role of sea ice and the importance of Arctic of commercial fish catches, from the 1950s onward, and shelves as migration routes, feeding and nursery areas for indicators of the sustainability of fisheries and ecosys- anadromous fishes, marine birds and mammals. tem structure (see Section 14.5.3) are well-documented for seven Arctic LMEs, i.e. the Barents, Norwegian, E and W Greenland, E and W Bering Seas together with 14.4.2.3. Commercial harvest the Iceland shelf (see Sherman & Hempel 2008). In the Exploitation and harvest of living marine resources other Arctic LMEs, commercial fisheries and subsistence has historically contributed to shape, and continues to harvest are estimated based on sparse data and records be a major stressor on, Arctic ecosystem biodiversity. (Sherman & Hempel 2008); therefore they are excluded The Steller’s sea cow Hydrodamalis gigas became extinct from this chapter. A recent study estimated that catches (IUCN 2008) in 1768, less than 30 years after the only in the Amerasian Arctic (FAO statistical area 18) from remaining Holocene population was discovered (in 1741) 1950 to 2006 were actually 75 times higher than what in the Bering Sea. Hunting records combined with life- was reported to the FAO, although these catches were history data indicate that overexploitation was the cause very low (Zeller et al. 2011). for this extinction (Turvey & Risley 2006). Commercial Arctic whaling from the 1700s onward has also severely Commercial Arctic and sub-Arctic fisheries harvest mil- depleted populations of almost all the baleen whale spe- lions of tonnes of fishes annually, for an economic value cies (Reeves & Kenney 2003). For example, the large reaching billions of US dollars. Commercial harvest population of resident bowhead whales between Green- ranged, in 2006, from approximately 100 thousand land and Svalbard was subject to intensive harvest during tonnes annually in the E and W Greenland LMEs to a the period of commercial exploitation by European maximum of approximately 1.3 million tonnes for the whaling vessels (1611-1911). At the end of this period, Iceland shelf and Norwegian Sea LMEs. For the W Ber- the initial resident population estimated at many tens of ing and Barents Seas LMEs, commercial fisheries yielded thousands appeared to be on the verge of extinction (Al- respectively approximately 1.1 million and 720 thousand len & Keay 2006, Wiig et al. 2007; see also Reid et al., tonnes in 2006 (Fig. 14.7). Large fluctuations in com- Chapter 3). mercial harvest, both in terms of numbers and species composition, have been observed over the past decades The historical harvest of marine birds is less clear be- in these LMEs. cause no logbook records of the sort available for marine mammals were kept by harvesters. The remaining Of significance, total landings in W Greenland have populations of flightless or near-flightless seabirds in the decreased dramatically since the early 1970s and, as in sub-Arctic (spectacled cormorant Phalacrocorax perspicil- other areas of the North Atlantic, have shifted from a latus and great auk Pinguinus impennis) were eliminated strong dominance of Atlantic cod to deep-water shrimp by over-harvest in the nineteenth century (Fuller 2001). (see Fig. 1.2 in Meltofte et al., Chapter 1). In E Green- Colonies of flying auks, particularly the thick-billed land and around Iceland, a similar shift is observed with murre Uria lomvia were decimated on the west coast of capelin now being the most abundant species in landings Greenland between the 1930s and 2000s, mostly by (Fig. 14.7). harvesting of breeding birds at the colonies, and have not recovered (Kampp et al. 1994, F. Merkel pers. com.; see In the Barents Sea, total landings were highest (3.3 also Ganter & Gaston, Chapter 4 and Huntington, Chap- million tonnes) during the mid-1970s, coinciding with 504 Arctic Biodiversity Assessment

2,500 Mixed group E Bering Sea King crabs 2,000 Atka mackerel Yellow n sole 1,500 Paci c snow crabs Flat shes Paci c herring 1,000 Chum salmon Paci c cod 500 Pink salmon Sockeye salmon 0 Alaska pollock 2,500 Mixed group W Bering Sea Japanese ying squid 2,000 Sockeye salmon Pink salmon 1,500 Chum salmon Squids Marine molluscs 1,000 Flat shes Crustaceans 500 Paci c herring Paci c saury 0 Alaska pollock 500 Mixed group W Greenland shelf Lumpsucker 400 Greenland cod Atlantic herring 300 Wolsh Deepwater red sh Ocean quahog 200 Haddock Greenland halibut 100 Red shes Northern prawn 0 Atlantic cod 500 Mixed group Greenland Sea Haddock 400 Ocean perch Saithe 300 Atlantic herring Greenland halibut Blue whiting 200 Northern prawn Deepwater red sh 100 Red shes Atlantic cod 0 Capelin 2,000 Mixed group Iceland shelf Deepwater red sh Northern prawn 1,500 Greenland halibut Blue whiting Ocean perch 1,000 Red shes Haddock 500 Saithe Atlantic herring Atlantic cod 0 Capelin 2,000 Mixed group Norwegian Sea Norway pout Greenland halibut 1,500 Tusk Red shes Atlantic mackerel 1,000 Haddock Blue whiting 500 Capelin Saithe Atlantic cod 0 Atlantic herring 4,000 Mixed group Barents Sea Blue whiting Greenland halibut 3,000 Atlantic mackerel Northern prawn Polar cod 2,000 Saithe Red shes 1,000 Haddock Atlantic herring Atlantic cod 0 Capelin 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Chapter 14 • Marine Ecosystems 505 a high dominance of capelin. Large fluctuations in total tens of kilometres long and 30 m high (e.g. Fosså et al. landings and yield of major species have occurred over 2002, Freiwald et al. 2002), which provide habitat for the past decades, likely due to fishing mortality and a rich community of invertebrates (Mortensen & Fosså environmental changes (e.g. Mathishov et al. 2003; also 2006). The coral Lophelia pertusa is widely distributed see Section 14.5.5). The Norwegian Sea also saw large and particularly abundant on the Norwegian shelf and fluctuations in total fish landings and their composi- slope, where bottom trawling has impacted many reefs. tion, particularly for herring and capelin. Over the past Harvest measures are now in place in Norway to protect two decades, total landings increased from less than the coral reefs from further damage (Fosså et al. 2002, half a million tonnes in 1990 to 1.5 million tonnes in Fosså & Skjoldal 2009). In the Canadian Arctic Archi- 2004 (Fig. 14.7). The E and W Bering Sea LMEs have pelago (Baffin Bay), restrictions have been placed on also seen large changes in fisheries catch over the past the Greenland halibut fishery to protect deep-sea coral decades, with a large increase in pollock landings in the habitats and over-wintering grounds of narwhal. The E Bering Sea since the 1980s and a decrease in the W bottom trawls posed a treat to several cold-water coral Bering since the 1990s (Fig. 14.7). species including the gorgonian species Acanella arbuscula and Paragorgia arborea (DFO 2007). Careful management of fishing stocks remains vital to Arctic biodiversity, as illustrated by the large fluctua- 14.4.3. Ocean acidification tions in landings and dramatic shifts in species composition in Arctic LMEs over the past decades. The paucity The oceans have absorbed about one third of the an- of baseline data and long-term monitoring in the Arctic thropogenic CO2 released to the atmosphere (Sabine et compared with other marine ecosystems, combined with al. 2004). This increase in CO2 concentrations in the rapid climate-associated changes, also speaks to using ocean contributes to ocean acidification. As the solubil- a precautionary approach for fisheries and resources ity of gases, including CO2, is higher in cold than warm management. In US waters of the Arctic, for example, waters, the Arctic Ocean is especially prone to acidifica- commercial fishing has recently been prohibited as tion (Bates & Mathis 2009). Ocean acidification reduces 2- per the Arctic Fisheries Management Plan until more the concentration of carbonate ions (CO3 ) and directly information is available to support sustainable manage- impacts a large and diverse group of marine organisms ment of potentially harvestable species (NPFMC 2009). that require carbonate ions to build their calcareous Sustainable yield is also central to commercial fishing in skeleton or shell, in the form of aragonite or calcite. This Arctic areas (e.g. Barents Sea) where fisheries resources taxonomically-diverse group includes protists such as constitute a major socio-economic driver. coccolithophores and foraminiferans, small planktonic animals such as pteropods, pelagic and benthic taxa such Subsistence fisheries are important in the Arctic and can as mollusks including sea urchins, shellfish and cor- influence marine ecosystems. In Hudson Bay, subsist- als, and fishes. Under typical conditions, the surface ence fisheries targeting mainly Arctic char, but also ocean is saturated with calcium carbonate (CaCO3), and polar cod and fourhorn sculpin Myoxocephalus quadricornis, calcareous shells or exoskeletons are subject to dissolu- reached almost 900 tonnes in 1962 to decline to ap- tion only at depths below the lysocline, where CaCO3 is proximately 300 tonnes by the early 2000s. This decline undersaturated. Model simulations predict that surface is attributed to the transition from sled dogs to snowmo- waters of the Arctic Ocean will become undersaturated biles as a means of transportation and the lesser need of with aragonite within a decade (Steinacher et al. 2009), local harvest as food for the dogs (Boot & Watts 2007). thereby reducing suitable habitat for calcifying species Such an example illustrates the effects of economic requiring aragonite. development and societal choices in directing the use of ecosystem services and in creating associated impacts Predicted changes in carbonate saturation have now been (see also Huntington, Chapter 18). substantiated with observations. In 2008, surface waters of the Canada Basin were found to be undersaturated Besides the direct impact of the catch, commercial har- with respect to aragonite, as a direct consequence of vest affects ecosystem biodiversity through impacts on extensive sea ice melt (Yamamoto-Kawai et al. 2009). habitats (particularly by botton trawling) and by-catch Aragonite is an essential constituent for the shell of the species as in other oceans (see also Josefson & Moki- pteropod Limacina helicina (see opening photo for chapter evsky, Chapter 8). For example, the reef-forming stony 8), an important plankton species found in the upper coral Lophelia pertusa forms massive reef complexes up to (top 50 m) Arctic Ocean. The same species is a promi- nent plankton species in the Ross Sea (Antarctica) and is considered an indicator of ecosystem health (Seibel & Dierssen 2003). There is experimental evidence that the Figure 14.7. Total landings of calcification of pteropod shells is reduced in response to commercial fish species (x 1,000 ocean acidification and conditions of aragonite undersat- tonnes) in seven Arctic Large uration (Orr et al. 2005, Comeau et al. 2009). Large re- Marine Ecosystems (source: ductions in L. helicina calcification rates are predicted for Sherman & Hempel 2008 and the Arctic, based on empirical relationships combined SeaAroundUs Project 2010). with model predictions for aragonite saturation (Comeau 506 Arctic Biodiversity Assessment

et al. 2012). Increased CO2 concentrations in the ocean intentionally introduced to the Barents Sea (Orlov & also influence biodiversity via species-specific effects on Karpevich 1965). The Barents Sea red king crab popula- macroalgal growth and photosynthesis (e.g. Mercado tion increased rapidly in the 1990s and now supports a et al. 1999, Gordillo et al. 2001). Recent experimental productive commercial fishery. The current distribu- work shows that CO2 stimulates growth in some species tion of red king crab is expanding eastwards in Russia such as the brown algae Alaria esculenta and Saccorhiza and westwards along the Norwegian coast (see UNEP/ dermatodea, negatively affects others such as Desmarestia GRID-Arendal 2010a) and is expected to spread north- aculeata, and has no effect on the growth rates of yet oth- ward. There has been much concern for the ecological ers species such as the red algae Ptilota spp. and Phycodris impacts of this introduced species on the ecosystem of rubens (F. Gordillo pers. com.). Therefore, changes in the Barents Sea (Jørgensen & Primicerio 2007). A com- Arctic Ocean chemistry are expected to affect popula- prehensive research program initiated in 2002 showed tions of calcifying species as well as other species af- that the red king crab feeds on a wide range of benthic fected by changes in the inorganic carbon cycle, thereby animals and that it may affect recruitment of some fish impacting biodiversity and trophic pathways within polar species through predation. marine ecosystems. The snow crab is native to the North Pacific and the 14.4.4. Range extensions and invasive species NW Atlantic and, in the Arctic, it is a native species in the Bering and Chukchi Seas and in W Greenland. The Species distribution range extensions and invasive spe- species is considered to have been introduced to other cies are considered to have a major impact on biodiver- Arctic areas via ballast waters (Kuzmin 2000). The sity at local and global scales, as they can disturb trophic snow crab was first detected in the Barents Sea in 1996 interactions and pathways, causing tremendous changes (Kuzmin 2000), then in Norwegian waters in 2003 in ecosystems (Wassmann et al. 2010, Weslawski et al. (Alsvåg et al. 2009). The abundance of snow crab has 2011, Lassuy & Lewis, Chapter 16). In the Arctic, the been increasing in the Barents Sea, where the species is low degree of endemism also suggests that range exten- now considered to have established a viable population sions may, at least temporarily, increase species and (Alsvåg et al. 2009). genetic biodiversity by the introduction of new species. However, this is not a gain to global biodiversity. 14.5. STATUS AND TRENDS IN Arctic marine ecosystems are influenced by advection from the Atlantic and Pacific Oceans (see Section ARCTIC MARINE ECOSYSTEM 14.3.1). Inflow shelves (sensu Carmack et al. 2006), BIODIVERSITY which are influenced by Atlantic (e.g. Barents Sea) and Pacific (e.g. Chukchi Sea) inflows, are susceptible to The world can tell us everything we want to know. The only range extensions of sub-Arctic species via the trans- » problem for the world is that it doesn’t have a voice. But, the port of planktonic larvae or adult animals (see Section world’s indicators are there. They are always talking to us. 14.5.4). However, interior shelves (e.g. Kara, Laptev, (Quitsak Tarkiasuk, Ivujivik). East Siberian Seas) are not directly subject to range extension through transport of sub-Arctic species. In these areas, range extensions are instead associated with 14.5.1. Historical and current status of Arctic increasing temperatures or the opening of migration/ marine ecosystem biodiversity transportation corridors with decreasing sea ice cover (Weslawski et al. 2010). The Arctic Ocean is young in terms of geology and biogeography. The evolutionary origin of marine inverte- Reduced ice cover extent and duration is expected brates, mammals and Arctic seaweeds reflects an ancient to favour northward migrations of sub-Arctic species Pacific origin dating back to the opening of the Bering (see Section 14.5.4). However, this may not necessar- Strait 3.5 million years ago (Adey et al. 2008). Through- ily lead to increases in abundance of species that are out most of the Tertiary, the Arctic Ocean region sup- also dependent on warm temperatures for survival and ported a temperate biota, and fully Arctic conditions reproduction. For example, the northward range exten- developed only during the latest part of this period. sion of bottom fish species typically observed in the This short history contributes to the presence of few southeastern Bering Sea is believed to be limited by cold endemic Arctic marine species on the shelves (Dunton bottom water temperatures together with the seasonal 1992, Adey et al. 2008) and the possibly lower diver- occurence of sea ice (Sigler et al. 2011). sity compared with lower latitude marine ecosystems (Tab. 14.1). Regional differences in species diversity can Introductions can be intentional or unintentional, as for also be related to time for diversification. For example, the red king crab Paralithodes camtschaticus and the snow there are over 350 benthic species in coastal Norwegian crab Chionoecetes opilio, respectively, in the Barents Sea. waters (Weslawski 2004), and these waters can supply The red king crab is a native species in the Bering Sea propagules for the Svalbard region. However, at present, where it supports a high value commercial fishery (e.g. only 80 intertidal benthic species have been identified for Kruse et al. 2000). In the 1960s the red king crab was Svalbard indicating that an increase in littoral diversity Chapter 14 • Marine Ecosystems 507

Table 14.1. Estimated number of taxa within Arctic seas (modified Section 14.5.3) is likely to have had important implica- after Bluhm et al. 2011 and references therein). tions for Arctic marine food webs. The extirpation of Group Estimated number of taxa bowhead whales and walruses from Svalbard is believed to have had major cascading effects on the marine Bacteria 4,500-450,000 ecosystem, contributing to the structure of present-day Archaea up to 5,000 ecosystems (Weslawski et al. 2000). Hence, planktivo- Protists 2,800 rous seabirds such as the little auk and polar cod prob- Macrophytes 160 ably took advantage of the abundance of zooplankton Invertebrates ~ 5,000 ‘freed’ by decreased predation from bowhead whales. Fishes 243 The increased abundance of pelagic fish would, in turn, have provided food for piscivorous alcids and gulls, sup- Birds 82 porting the development of the large bird colonies found Mammals 16 on Svalbard. Similarly, common eiders Somateria mollissima and bearded seals Erignathus barbatus, both benthic feeders, would have benefited from walrus exploitation can be anticipated in the future since both areas have (Fig. 14.8). In the same way, it is likely that pre-historic similar coastal geomorphology and water mass charac- human interventions in Arctic ecosystems led to altera- teristics (Weslawski et al. 2010). tions of Arctic biodiversity composition and ecosystem functioning (see Meltofte et al., Chapter 1). So far, the biodiversity of the marine Arctic is poorly documented, and current estimates suggest that many Present-day ecosystems have evolved from past condi- species are yet to be discovered (Ausubel et al. 2010, tions and pressures on their various components. Cur- Bluhm et al. 2011), although the Census of Marine Life rently, changes in the diversity and in the structure and has added substantially to the inventory (e.g. Piepenburg functionality of Arctic marine ecosystems are taking et al. 2011). As an example, a recent survey of zooplank- place at a rapid pace, associated with local/global pres- ton composition in the Arctic basins found 25% of the sures on these ecosystems, northward shifts in pelagic species observed had not previously been recorded in the and benthic assemblages, and new introductions (see Arctic (Kosobokova et al. 2011). previous Section). Here, we present observations of current changes and trends in Arctic marine ecosystems At geological time scales, the distribution of foraminifers in relation to the stressors described above. However, and other biological proxies fluctuated strongly between it is essential to bear in mind that ecosystem responses interglacial/glacial periods, attributed to changes in pro- are complex and cannot be ascribed to a single driver ductivity (see Darby et al. 2006 and references therein). due to the confounding effects of multiple stressors that Retreat and recolonization of cold-temperate species in could be acting in synergy or in opposite directions, and the Arctic is well known to have occurred in the past at varying time scales. This is exacerbated in the Arctic during the glacial and interglacial periods, respectively where interannual climate variability (See Box 14.4) and (Lüning 1990 and references therein). rapid climate change combined with intensified anthropogenic pressures may simultaneously affect species At shorter time scales, the removal of vast numbers of (e.g. reproduction, growth), community (e.g. predation, marine mammals and their associated biomass from Arc- competition) and ecosystems (e.g. type of production, tic ecosystems over a few decades to a few centuries (see food web interactions).

16th Century Present day

Primary production Primary production 860 860

Zooplankton production Zooplankton production 50-200 50-200

Planktivorous birds Pelagic shes Planktivorous birds Pelagic shes 0.2-1 0.2-1 0.6-2 3-9

Bowhead whales Piscivorous birds & seals Piscivorous whales & seals Piscivorous birds 13-50 0.02-1 0.2-1 0.2-1

Figure 14.8. Schematics of historical and contemporary pelagic coastal food webs off Svalbard, assuming comparable primary and secondary production. Values are consumption in Kcal per m2 per year. Thickness of arrows is relative to consumption values. (Source: Weslawski et al. 2000.) 508 Arctic Biodiversity Assessment

Box 14.4. How the atmosphere influences Arctic marine ecosystems

5.5 The North Atlantic Oscillation (NAO) is an a) important index of the interannual variabil- 5.0 ity in the atmospheric circulation across the ) North Atlantic, with low frequency variabil- 4.5 ity on multi-year to decadal time scales. It 4.0 is associated with changes in temperature WSC (°C and the current regimes of the entire North 3.5 Atlantic. The NAO index is defined by the 3.0 co-variability of average atmospheric sea emperature T level pressure between the Icelandic Low 2.5 Temperature and the Azores High, the major pressure Temperature (3 year mean) systems over the North Atlantic. When 2.0 both are strong (i.e. Icelandic Low lower 0.8 1.4 than normal and Azores High higher than b) normal), the NAO index is positive and the 0.6 1.6 westerly winds across the Atlantic intensify. (H’) 0.4 A positive NAO phase has been associated

x 1.8 with a stronger Atlantic inflow and tem- 0.2 peratures higher than normal in the Barents O Inde 0 Sea, whereas a negative NAO phase has an 2.0 NA opposite effect (reduced Atlantic inflow and –0.2 lower temperatures) (e.g. Blindheim et al. 2.2 Species Diversity Index 2000, Ingvaldsen 2005). –0.2 Species Diversity Index (H’) NAO Index (3 year mean) The Arctic Oscillation (AO), defined by –0.6 2.4 Thompson & Wallace (1998), is the domi- 1980 1985 1990 1995 2000 nant mode of variability of Northern Hemi- Box 14.4 Figure 1. a) Mean autumn (August-September) temperature of the West sphere sea level pressure. Another name Spitsbergen Current at about 79° N between 100 and 300 m depth. b) Correlation be- for the AO is the Northern Annular Mode tween the NAO Index (3-year mean calculated from September-August) and Shannon- (Wallace & Thompson 2001). Changes in Wiener diversity index (H’). The secondary y-axis scale (species diversity) is inverted. the AO impact the pattern and velocity of (Source: Beuchel et al. 2006.)

14.5.2. Observations with respect to climate- (e.g. ringed seals) and foraging success (e.g. polar bears) associated changes of ice-associated species (summarized in Kovacs et al. 2011a). Changes in snow and sea ice conditions also in- The decline in sea ice extent directly impacts ice-asso- directly affect pelagic and benthic communities through ciated species and food webs, as sea ice serves as habitat changes in stratification, light attenuation and nutrient for a variety of species, providing feeding and reproduc- availability. There is growing evidence of a freshening tion areas for ice-associated fauna including ice-endemic and warming of surface waters in the Canada Basin, amphipods, fishes (e.g. polar cod), seals, whales and largely attributed to sea ice melt (McPhee et al. 2009, polar bears (see Kovacs et al. 2011b, Vincent et al. 2011). Proshutinsky et al. 2009). Associated with these physical On-going changes in sea ice conditions are expected to changes, the community composition of pelagic primary impact ecosystem biodiversity at various scales, from producers is also changing. The abundance of small algae millimeters to hundreds of kilometers. Changes in sea is increasing whereas that of large algae is decreasing as ice structure directly affect the habitat of viruses, bac- the former have a competitive advantage over the latter teria and protists that are found in abundance in Arctic (Li et al. 2009). If this trend towards a community of sea ice and support the sea-ice associated food webs (see smaller cells is sustained, it may lead to reduced bio- Lovejoy, Chapter 11). The rapid melting of ice shelves logical production at higher trophic levels as the size and associated loss of unique microbial habitats may also structure of phytoplankton communities is a strong constitute an irreversible loss to Arctic ecosystem biodi- determinant of trophic pathways and carbon fluxes in versity (see Box 14.5). marine ecosystems. In addition, changes in the timing of the productive period can have major cascading impacts Changes in sea ice surface conditions (e.g. snow cover, on Arctic marine food webs since the synchronization of presence and location of ridges) impact the reproduction events is a key factor in the transfer of primary produc- Chapter 14 • Marine Ecosystems 509

Box 14.5. Vanishing ice shelves and melting icebergs ice motion in the Arctic Ocean (Darby et al. 2006). Mass balance estimates for the Greenland Ice Sheet indi- Another atmospheric pattern, the Arctic Dipole cate an overall loss of ice since the early 1990s. This loss has (AD) anomaly (also referred to as the Arctic Rapid increased rapidly in recent years, from a yearly average of Change circulation pattern; Zhang et al. 2008) pro- about 50 Gt between 1995-2000 to about 160 Gt between duces strong meridional winds that export sea ice 2003-2006 (AMAP 2011). The fragmentation and loss of ice from the western to the eastern Arctic. The dipole sheets and glaciers is expected to continue at an accelerated anomaly is considered a key driver of the record pace in a warming climate (Mueller et al. 2003, AMAP 2011). low summer sea ice extent observed in 2007 (Wang et al. 2009). The formation and release of ice islands and icebergs are important episodic events that introduce freshwater, micro- In turn, changes in sea ice patterns influence nutrients, dust and other particles to polar marine ecosys- where the ice melts and ice-associated material is tems (Arrigo et al. 2002, Geibert et al. 2010). In August 2010, a released, impacting ecosystem productivity and 40 m thick, 54 km2 section of ice was released from the Ward biodiversity. A study of benthic communities in Hunt Ice Shelf on Ellesmere Island, Canadian Arctic Archi- Kongsfjorden, Svalbard, over the period 1980-2003 pelago (NASA observations). This ice shelf, estimated to be has linked changes in benthic community structure 3,000 to 5,000 years old, is the oldest sea ice in the Northen to the NAO and its local manifestations via the West Hemisphere (England et al. 2008). During the same month, a Spitsbergen Current (Beuchel et al. 2006). Severe 250 km2 ice island was released from the Petermann Glacier changes in the benthic community were observed in N Greenland. This ice island was the largest Arctic iceberg between 1994 and 1996 coinciding with a shift in recorded since 1962. Extensive glacier melt and break-off NAO from positive to negative mode (Box 14.4 Fig. continued in Greenland in 2012, with the release of a 150 1). The change in biodiversity was accompanied by km2 section also from the Petermann Glacier. The Petermann a decline of sea anemones (actinarians) and the ap- Glacier is fed by the Greenland Ice Sheet and is replaced pearance of dense carpets of brown algae (Beuchel by ice forming upstream. However, ice shelves such as the et al. 2006). At higher trophic levels, regime shifts Ward Hunt Ice Shelf are formed by centuries of accumulated associated with the NAO have shown important snow and compressed sea ice, and are at risk of vanishing effects on circumpolar murre populations, with altogether as sections released into the sea are not replaced populations in the North Pacific and NW Atlantic (England et al. 2008). A rare type of ecosystem associated sectors trending in opposite directions from those with the Ward Hunt Ice Shelf was an ‘epishelf’ lake of fresh- in the eastern Atlantic (Irons et al. 2008; see Box 4.3 water that was contained by the ice of the shelf. In 2002, the in Ganter & Gaston, Chapter 4). fracturing of the ice shelf caused almost complete loss (96%) of the localized fresh and brackish water habitats that were known to support unique communities of organisms (Van Hove et al. 2001, Mueller et al. 2003). tion to secondary producers and the efficiency of transfer of material through the food web (Michel et Icebergs can survive for many years in Arctic waters before al. 1996, 2006, Leu et al. 2011). being exported and melting completely. While present they can impact both benthic and pelagic habitats. Their deep Alternatively, a longer open water period has been keels scour and carve the ocean floor. Icebergs that become linked to increased primary production (Arrigo et al. grounded can disrupt local circulation, potentially becoming 2008, Pabi et al. 2008), and increased wind mixing a physical barrier to oceanographic processes such as advec- creates favorable conditions for upwelling of nutrient- tion of nutrients, sea ice drift and the extent/duration of ice rich waters, thereby increasing pelagic (Tremblay cover (Arrigo & van Dijken 2003). Such impacts of icebergs et al. 2011) and sea ice (Mundy et al. 2009) produc- can significantly inhibit primary production (e.g. reductions tion by large phytoplankton. These large cells are of 40% observed in the Southern Ocean; Arrigo et al. 2002) important for energy transfer to higher trophic levels thereby impacting upper trophic levels including sea birds in marine food webs. Since the ability of the Arctic and marine mammals. macroalgal community to respond to nutrient input during summer is restricted to a few nitrophilic spe- The presence and movement of icebergs alter water column cies (Gordillo et al. 2006), more frequent upwelling stability through mixing and the release of freshwater associ- events associated with extended open water periods ated melt. These can either enhance or disrupt the produc- may not impact macroalagal communities in the tivity of the area. In the Southern Ocean, the biomass of Arctic. primary producers can be > 30% higher in the wake of mov- ing icebergs (Schwarz & Schodlok 2009) leading to increased With respect to benthic diversity, the lack of light- biodiversity within the vicinity of the icebergs, including the attenuating sea-ice cover and reduced ice-scouring presence of whales (Geibert et al. 2010). 510 Arctic Biodiversity Assessment will certainly result in new habitats available for seaweed movement and distribution of whales and other ‘open colonization (Müller et al. 2009, Weslawski et al. 2011). water’ species, modifying species diversity and trophic In particular, the rocky Arctic islands off the Russian interactions in Arctic marine ecosystems (see Section mainland, as well as the rocky coastlines of Kola Pen- 14.5.4 and Reid et al., Chapter 3). insula, Svalbard, Greenland (Baffin Bay and Greenland Sea) and the Canadian Arctic Archipelago, will experi- 14.5.3. Observations with respect to marine ence milder environmental conditions and hence may provide new habitats for temperate seaweeds that may resources exploitation outcompete polar species. Commercial fishing is considered a major force influencing ecosystem structure and functioning by altering Local changes in polar bear distribution, population community composition and species interactions within sizes (e.g. Aars et al. 2009), physiological condition them. Fisheries impacts are documented in LMEs by us- (Pertoldi et al. 2009), reproductive success and survival ing standard indicators including a marine trophic level (e.g. Parks et al. 2006, Stirling 2009, Regehr et al. 2010) index and estimates of the primary production required have been linked to decreases in sea ice cover extent and to sustain landings (Sherman & Hempel 2008). How- shorter ice-covered periods in the Arctic. The absence of ever, while these and other ecosystem indicators allow summer sea ice is also seen as a key factor in the recent monitoring of trends, causal relationships to explain the hybridization of polar bears and grizzly bears Ursus observed changes are not yet clearly established due to arctos. In 2006 and 2010, two hybrid ‘grolar’ bears were the complex nature of ecosystem responses. observed in the western Canadian Arctic. DNA analysis confirmed that the ‘grolar’ bears were hybrids between In W Greenland, Atlantic cod was dominant in the polar and grizzly bears, with a second-generation hybrid fisheries catch during 1950-1970, therefore the high found in 2010. This indicates that there may be more trophic index shown in Fig. 14.9. From 1970 onward, interbreeding between species that do not typically co- the decrease in trophic level reflects a shift from Atlantic exist, as environmental conditions change in the Arctic. cod to deep-water shrimp dominance in the ecosystem (see Fig. 6.15 in Christiansen & Reist, Chapter 6). While In northern Hudson Bay, an increase in the duration of such a trend implies ‘fishing down’ of the ecosystem, the open water period has been associated with a change the shift in community structure and landing composi- in the diet of marine birds, with increases in the im- tion also coincides with a rapid change in climatic and portance of capelin, sand lance Ammodytes sp. and mysid oceanographic conditions, related to a shift in the NAO crustaceans and decreases in the importance of polar cod (Dickson et al. 2000, Buch et al. 2004). The drastic and hyperiid amphipods (Gaston et al. 2009, see Fig. 4.6 decline in Atlantic cod was related to a reduction in re- in Ganter & Gaston, Chapter 4). These changes were si- cruitment, itself related to low spawning stock biomass multaneous with an advance of about three weeks in the and temperature, whereas the growth and recruitment timing of ice break-up in the region, yet the timing of of shrimps would have been favored by low tempera- egg-laying has not advanced to keep pace with changes in tures and reduced predation (Buch et al. 2004). This ice conditions. This has resulted in lowered recruitment ecosystem shift had tremendous economic impacts as the in years when egg-laying is late relative to ice break-up Greenland export economy, formerly highly dependent and an overall deterioration in the condition of murre on the cod fishery, is now almost entirely dependent on chicks at colony departure (Gaston et al. 2009). In paral- shrimp exploitation (Garcia 2007). lel with these changes, shifts in top predator species are expected to influence ecosystem structure by increasing A decline in the mean trophic level index also occurred competition for food resources among resident mammals in E Greenland and around Iceland, somewhat similar to (Higdon & Ferguson 2009; see Section 14.5.4). W Greenland. In this case, the cod-dominated fishery shifted to small pelagic fishes, mainly capelin. In the Overall, the decrease in Arctic sea ice extent can be con- Barents Sea, the mean trophic level declined from the strued as habitat fragmentation, restraining the distribu- 1950s to the mid 1990s and showed large fluctuations tion and movement of species that use the ice for trans- thereafter (Fig. 14.9). These fluctuations are linked to portation (e.g. polar bear). However, an increase in first the Barents Sea capelin stock, potentially the largest year ice at the expense of multi-year ice may provide stock worldwide, which showed large variations and increased habitat for some ice-associated species given collapsed on three separate occasions over the past three that changes in the phenology of events (e.g. timing of decades (Fig. 14.9). Notably, a significant decline in ice melt) does not compromise key life history func- 1986 led to the complete closure of the capelin fishery tions (e.g. reproduction and rearing). At the same time, from 1994 to 1998. The causes of the large variations the associated increase in open water area and period and decline in capelin stock have been attributed to mul- facilitates migration and movement of some species that tiple stressors including fisheries, climate and ecological avoid the ice. There is evidence that the presence of sea interactions among species (see Section 14.5.5.2 and Fig. ice in certain areas, considered ‘choke points’, constrains 1.3 in Meltofte et al., Chapter 1). the distribution of ice-avoiding predators such as killer whales (Higdon & Ferguson 2009). Opening of these With respect to commercial whaling, current observa- ‘choke points’ with continued sea ice melt may alter the tions show population recovery after cessation of activi- Chapter 14 • Marine Ecosystems 511

3.7 E Bering Sea ties (Box 14.6), suggesting some degree of reversibility of ecological changes with timely action. 3.6

3.5 14.5.4. Observations with respect to range extensions 3.4 Geographical shifts and range extensions are currently taking place in the marine Arctic in response to warm- 3.3 3.7 ing, sea ice decline and changes in water mass distribu- W Bering Sea tion (e.g. Wassmann et al. 2010).

3.6 Major distribution changes have been documented in

3.5 sub-Arctic waters over the last decade. Major biogeographic changes in the biodiversity of a key zooplankton group, calanoid copepods, have been reported for the 3.4 North Atlantic (Beaugrand et al. 2002a, 2002b, 2009). The observed rates of biogeographical expansion appear 3.3 4.5 to be far greater than those in terrestrial systems, likely W Greenland Shelf due to the fluid nature of the pelagic domain and the relatively short life cycles of these species (Beaugrand 3.5 et al. 2009). Similar northward range extensions have been observed for phytoplankton (Hegseth & Sundfjord

3.0 2008), benthic invertebrates (e.g. Sirenko & Gagaev 2007) and fish (e.g. Mueter & Litzow 2008, Mecklen- burg et al. 2011). 2.5 4.5 Greenland Sea A warming period over the entire northern North At- lantic began during the 1920s and 1930s, with tempera-

3.5 tures warmer than normal and enhanced Atlantic inflow in the Barents Sea during the mid-1900s (Drinkwater 2011). Associated with this warm period was a north- 3.0 ward range extension of Atlantic cod as far north as W Spitsbergen (Fig. 14.10), with an increase in population around Bear Island that was large enough to re-establish 2.5 4.5 a fishery after almost 40 years of absence. According to Iceland shelf Drinkwater (2011), the warm temperature increased cod growth rates which, together with good recruit- 3.5 ment, resulted in the largest recorded cod biomass in the Barents Sea. Other colder water species such as capelin and polar cod retreated northward in the Barents Sea, 3.0 and haddock Melanogrammus aeglefinus moved eastward towards Novaya Zemlya. Herring extended their range

2.5 eastward such that a Russian fishery was established off 4.5 the Murman coast in the 1930s (Drinkwater 2011). (See Norwegian Sea also Christiansen & Reist, Chapter 6.)

3.5 Broad biogeographical changes of key structural seaweed species are predicted for both hemispheres due to 3.0 warming of marine coastal systems (Müller et al. 2009). The predicted poleward shift of forest kelp seems to be in progress right now as this species has already been re- 2.5 corded in secluded fjords in southern Spitsbergen, Sval- 4.5 Barents Sea bard (Peltikhina 2002, Olsen et al. 2004). A geographi-

3.5

Figure 14.9. Mean trophic levels 3.0 in seven sub-Arctic and Arctic Large Marine Ecosystems. Source: Sherman & Hempel (2008), 2.5 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 SeaAroundUs Project (2010). 512 Arctic Biodiversity Assessment

Box 14.6. Bowhead whale population recovery

The historical population of bowhead whales in the Beaufort 14,000 Sea, estimated to number between 10,400 and 23,000, was 12,000 reduced by commercial whaling to about 3,000 individuals e by the early 1900s, when commercial whaling of this species 10,000 ceased. However, as of 2001 the bowhead whale population had recovered to an estimated 7,700-12,600 individuals, 8,000 increasing at a rate of 3.4% per year between 1978 and 2001 6,000 (Box 14.6 Fig. 1; see also Reid et al., Chapter 3). An increase in 4,000

bowhead whale sightings in other Arctic regions is also ap- Estimated abundanc parent from traditional ecological knowledge: 2,000

…here is the place [outer Frobisher Bay] where 0 1975 1980 1985 1990 1995 2000 2005 » the bowhead whales are now being spotted more frequently practically every summer, it seems that the bowhead Box 14.6 Figure 1. Abundance estimates for the western Arctic whales are increasing in numbers every year here. bowhead whale stock in the Beaufort Sea, 1978 to 2001. Vertical bars (Josie Papatsie in NWMB 2000). are standard deviations. (Source: Zeh & Punt 2005.)

a) cal shift of seaweed species in response to temperature Depth (m) 0-50 fluctuations has been documented in the past (Hiscock et 50-100 100-150 al. 2004, Hawkins et al. 2008). The interplay of photo- 150-200 periodic responses, temperature and other interactions 200-250 250-300 will not only change geographic distribution patterns but 300-400 400-500 may also influence seaweed phenology (Wiencke et al. 500-1,000 > 1,000 2009). Similar complex interactions between environmental forcings and the responses of individual species and the interactions among species are expected to occur at multiple trophic levels, impacting Arctic ecosystem architecture and biodiversity.

Increases in several marine bird species have been reported in Arctic areas. In Hudson Bay and Hudson Strait, both razorbills Alca torda and great black-backed gulls Larus marinus, typically sub-Arctic species, have increased over the past two decades (Gaston & Woo 2008). In Spitsbergen, both great skua Stercorarius skua and great black-backed gull are expanding their range b) (Anker-Nilssen et al. 2000, H. Strøm pers. com.), while in the Beaufort Sea horned puffins Fratercula corniculata have appeared and established themselves as breeders (Divoky 1982). The first sighthings of breeding pairs of northern gannets Morus bassanus in northern Svalbard, 500 km north of their normal range, also speaks to impacts of a warming climate (Norwegian Polar Insti- tute 2011). In Hudson Bay, the first documented sighting of killer whales about 50 years ago and their significant increase in recent years have been linked to reduced sea

Figure 14.10. Schematic distribution of NE Atlantic cod Gadus morhua in the Barents Sea a) prior to and b) during the 20th century warm period (source: Drinkwater 2011). Chapter 14 • Marine Ecosystems 513

100 production has shifted between warm and cold years. Hudson Bay During cold years (e.g. early 1970s), when sea-ice re- Hudson Strait mains until mid-March or later, ice edge phytoplankton 80 Foxe Basin blooms are observed in early spring (Alexander & Nie- James Bay - eastern Hudson Bay bauer 1981, Hunt et al. 2002) contributing significantly to total annual production. With a shift to warmer 60 waters (e.g. > 3 °C), when sea ice is absent or retreats before mid-March, maximum primary productivity and phytoplankton biomass occurs during an open-water 40 bloom in May or June (Whitledge et al. 1986, Hunt et al. 2002). Despite these changes in primary production regimes, there has been no significant change in total 20 annual net primary production (NPP) over the past four decades in the southeastern Bering Sea (Jin et al. 2009). However, there is evidence of changes in the fate 0 of primary producers, with more primary production 1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005 reaching the benthos during cold years and more spring primary production channeled into pelagic components Figure 14.11. Trend in killer whale Orcinus orca observations in the during warm years. Hudson Bay region, Canada (sources: Hidgon & Ferguson 2009 and Higdon et al. 2011). Zooplankton and fishes do not respond as quickly as primary producers to climate-associated changes. However their responses have been conspicuous, impacting preda- ice cover extent (Fig. 14.11). Here, it is the change in sea tor-prey interactions and energy flow within the Bering ice conditions, associated with increased accessibility to Sea ecosystem. It was assumed that zooplankton, spe- open water areas, that is determinant for the range ex- cifically copepods, would grow more rapidly and would tension observed. Cascading effects on the ecosystem are graze more primary production in warm years. However, expected as killer whales compete with resident marine new data suggest that this assumption is incorrect. Key mammals for food resources. species such as the lipid-rich copepod Calanus marshallae are less abundant in warmer years, and there is no change 14.5.5. Case studies in the abundance or biomass of small neritic species (e.g. Acartia spp.) between the different temperature regimes (Hunt et al. 2010). Understanding the response of zoo- 14.5.5.1. Ecosystem regime shifts in the Bering Sea plankton to regime shifts is essential, since key copepod species such as C. marshallae, along with euphausiids, con- In the past three decades, major changes have occurred stitute up to 70% of juvenile and adult pollock diets and in the marine ecosystem of the southeastern Bering Sea are also important in the diets of juvenile salmon entering (e.g. Vance et al. 1998, Hunt et al. 2002, 2011, Schu- the Bering Sea (Aydin et al. 2007, Moss et al. 2009). macher et al. 2003). Persistent changes in the atmosphere and upper ocean fields along with corresponding Regardless of the lower availability of C. marshallae shifts in the abundance and species of zooplankton and during warm years, there is rapid growth of the small fish indicate the occurrence of climate regime shifts in (age-0) pollock that feed during spring and early sum- 1926, 1945, 1976 and 1998 in the northeastern Pacific mer. Yet, increased predation by juvenile salmon, larger (Peterson & Schwing 2003). The marine ecosystem pollock and other fish species on age-0 pollock, due of the Bering Sea has been shown to respond to the to the scarcity of lipid-rich copepods and euphausids, large-scale climate regime shifts of the Pacific Decadal leads to poor survival of the small pollock (Moss et al. Oscillation (PDO), as well as the regional Aleutian Low 2009, Hunt et al. 2011). Additionally, the reduction in Pressure System and Arctic Oscillation (AO), smaller- the availability of C. marshallae and euphausiids in warm scale episodic weather events, rising global temperatures years may impact the survival of age-0 pollock directly and declining sea ice (Bond & Overland 2005, Greb- due to energetic constraints. Recent evidence suggests meier et al. 2006a). The climatology and oceanography that the small pollock have near or below the amount of the southeastern Bering Sea reveal a change from an of stored lipids that they require to survive winter in ecosystem dominated by Arctic species for most of the years with early ice retreat and warm spring and sum- 20th century, with a gradual replacement by sub-Arctic mers (Hunt et al. 2011). Therefore, while the availability species in the last 30 years (Wang et al. 2006). of lipid-rich copepods is crucial for the production of strong pollock year classes, other factors such as preda- The regime shifts have impacted all levels of the Bering tion impact their survival and ultimately the pollock Sea food web and have had significant economic impacts stocks across regime shifts (Fig. 14.12). due to changes in the abundance of salmon, crab and groundfish (NRC 1996, Schumacher et al. 2003). At the Pollock, specifically walleye pollock Gadus chalcogrammus, base of the food web, the timing and location of primary represent the largest major fishery in the eastern Ber- 514 Arctic Biodiversity Assessment

Warm year with late bloom and few large copepods or euphausiids Figure 14.12. Differences in trophic pathways based on availability of the copepod C. marshallae and the euphausiid T. raschii on the southeastern Bering Sea shelf. When these species are not available, preda- Winter tion and cannibalism of age-0 starvation pollock increases, as does overwinter mortality of age-0 pollock Cold year with early bloom and abundant large copepods and euphausiids due to insufficient energy stores. In contrast, when the zooplankton are abundant, cannibalism and predation decrease and energy stores may increase resulting in stronger recruitment of age-1 pollock. (Source: Hunt et al. 2011.)

MesozooplanktonAge-OsLarger pollockAge-1s ing Sea. Increases in water temperatures were previ- ades, fishery catches and their composition have varied ously expected to benefit the fishery (Hollowed et al. significantly (see Section 14.4.2). The capelin stock has 2001, Mueter et al. 2006). However, based on the above shown large variations, collapsing on three separate oc- observations of pollock survival in regime shifts, a recent casions with a > 90% reduction in stock size followed by model indicates that pollock recruitment could decline rapid recoveries (ICES 2006, 2009, Sherman & Hempel 32-58% by 2040-2050 (Mueter et al. 2011). Extended 2008). The cause of the large variations and decline in periods of warm conditions leading to a re-occurrence of the capelin stock have been attributed to complex inter- weak year classes may make fishing pressure unsustain- actions of multiple stressors including fisheries, climate able relative to periods with strong year classes (Hunt and ecological interactions amongst species (Stenseth et et al. 2011). These temporal considerations for fisheries al. 2002, Hjermann et al. 2004, Lindstrom et al. 2009). management should also be coupled with considerations of shifts in spatial distributions of fishes. For example, in- Among the different fish species undergoing changes in creasing bottom temperatures may affect the distribution their stocks, there exist strong trophic (i.e. predator- of fish, with warm temperatures allowing many ground- prey) interactions involving the size and distribution of fish species to extend their distribution range northward different year classes (O’Brien et al. 2004, Lindstrom and eastward in the Bering Sea (Hunt et al. 2008). et al. 2009). Consequently, the impact of stressors on one species is transferable to other fish, mammals and bird species via food web interactions. In the Barents 14.5.5.2. Complex ecological interactions in the Sea, capelin are key prey items for Atlantic cod (e.g. Barents Sea Bogetveit et al. 2008) and the common murre Uria aalge The Barents Sea is an ecologically productive region (Bogstad et al. 2000) and are the most effective grazers with economically important commercial fisheries. It on zooplankton in the central and northern part of the holds some of the largest fish stocks in the world includ- ecosystem (Gjøsæter 1998). The migration of the capelin ing Atlantic cod, polar cod, capelin and Atlantic her- also transfers large amounts of energy from the northern ring (O’Brien et al. 2004). These species play a critical portion of the sea to other species found only within the role in the ecosystem structure of the Barents Sea. To southern and coastal regions (Hjermann et al. 2010). model and predict changes in the Barents Sea ecosystem, Consequently, the capelin collapses had repercussions interactions between climate change and other factors both downward and upward in the food web (Gjøsæter influencing species interactions must be taken into con- et al. 2009). Reduced capelin abundance led to decreased sideration. In the Barents Sea, fishing and climate change predation and increased zooplankton biomass while are the main stressors together with offshore oil and gas impacting capelin’s predators in various ways. Decreased exploration, increasing marine traffic, heavy metal and growth and increased cannibalism among cod, increased organic contaminants as well as the potential for radioac- mortality and recruitment failures leading to the loss of tive pollution. These stressors influence ecosystem food over 200,000 pairs of common murres, and food short- webs and habitats. age and coastal invasions of harp seals Phoca groenlandica were all associated with the first capelin stock collapse Trends and variability in the Barents Sea ecosystem are (Gjøsæter et al. 2009). Ecosystem impacts were differ- relatively well documented. Over the last few dec- ent in later collapses, likely due to increased availability Chapter 14 • Marine Ecosystems 515 of alternative food for predators (see Fig. 1.3 in Meltofte their potential use of the newly available habitat will et al., Chapter 1). This highlights the importance of ultimately depend on compounded effects from exploita- trophic interactions and the role of functional groups in tion, predation and competition as well as mixed factors maintaining trophic pathways and food web transfers in affecting the biology and life history of the species Arctic marine ecosystems. (Roderfeld et al. 2008).

Multiple stressors are also impacting habitat character- 14.5.5.3. Changes in the structure and function of the istics in the Barents Sea. Of key importance are changes W Greenland pelagic ecosystem in water temperature and sea-ice dynamics, including the location of the marginal ice zone (MIZ). The Barents Disko Bay, W Greeland, has been the site of Arctic Sea has experienced warming (e.g. 1900-1920s, 1970- research since 1906. Since 1992, the seasonal plankton 1980s) and cooling (e.g. 1930-1950s) periods over the community structure, succession and production at a last century (Ingvaldsen & Loeng 2009). The most re- 300 m deep station off Godhavn/Qeqertarsuaq has been cent warming trend continues with water temperatures investigated (Levinsen et al. 2000, Madsen et al. 2001, increasing by 1.5 °C since the late 1970s/early 1980s 2008a, 2008b). Disko Bay is a very productive area (Skagseth et al. 2008). The currently observed warm- and is very important for commercial and recreational ing appears to be driven by the advection of Atlantic fishing and hunting. The bay is located at the outlet of water into the Barents Sea, which is now warmer and Jakobshavn Isbræ, the most productive glacier in the more saline due to increased heating and evaporation northern hemisphere. Icebergs calved from the glacier in the sub-tropics (Drinkwater et al. 2009). Changes in float down the fjord and lie stuck on the bottom of its the advection of Atlantic water impact not only water shallower mouth until they are broken up by the force of temperatures but also the position of the Polar Front the icebergs behind them. and the MIZ (Loeng 1991, Ellingsen et al. 2008; see Fig. 8.9 in Josefson & Mokievsky, Chapter 8). The Polar Glacier ice production and sea ice from Disko Bay sub- Front, which separates the Polar and Atlantic waters in stantially influence the initiation of the productive cycle the Barents Sea, and the MIZ are biologically produc- of the plankton community. The intense spring phyto- tive habitats (Sakshaug & Skjoldal 1989, Roderfeld et al. plankton bloom starts as the sea ice breaks up, allowing 2008) and fertile feeding grounds for fishes such as cape- light to enter the water column, and quickly depletes lin which migrate to the MIZ during summer (Hassel surface water nitrate concentrations. The spring phyto- et al.1991), and immature capelin overwintering in the plankton production provides a major source of nutrition region of the Polar Front (Loeng & Drinkwater 2007). for secondary producers (e.g. calanoid copepods) and is thus an essential contributor to marine food webs. Since Therefore, changes in habitat characteristics such as wa- reproduction is one of the most nutritionally demand- ter temperature and the distribution of water masses and ing stages of the life cycle in Calanus spp., reproductive the fronts separating them, will impact species distribu- success for these copepods depends on synchronization tion, reproduction and ecological interactions among with the phytoplankton bloom (Fig. 14.13; Madsen et species. A recent model evaluating ecosystem changes al. 2008b) and subsequent replenishment of their lipid in response to warming scenarios shows differential stores (Lee et al. 2006). responses of zooplankton species, with a decrease in the production of Arctic Calanus glacialis and an increase in Traditionally, pelagic research has focused on bloom the production of Atlantic C. finmarchicus in a warmer dynamics and transfers to large Calanus copepods. Con- climate (Slagstad et al. 2011). Past observations have sequently, the pelagic food web is typically modeled as a shown enhanced recruitment and a northward shift in simple food chain from nutrients via large phytoplankton spawning for fishes during warming periods in the Bar- and copepods to upper trophic levels, whereas micro- ents Sea. Such trends are occurring again for fishes such bial processes are described as a simple degradation rate as capelin and cod (Sundby & Nakken 2008, Drinkwater of detritus. However, the small species and stages of 2011; also see Section 14.5.4) as well as for invertebrate zooplankton and the diverse microbial community play species. Krill biomass has increased during the last a key role in determining the amount of nutrient and decade in response to increasing temperatures, despite organic matter that is kept in the euphotic zone after the heavy predation from capelin over the same time period spring bloom. Studies on the succession and composition (Eriksen & Dalpadado 2011). of the zooplankton community have shown that small copepods are present in the water column year round Decreasing sea ice cover and the northern retreat of and dominate from late summer and throughout winter the MIZ is also impacting the Barents Sea ecosystem. (Madsen et al. 2008a). Another group of zooplank- Model results indicate that the MIZ will be displaced ton, the protozooplankton (ciliates and heterotrophic farther offshore in the future (Ellingsen et al. 2008), dinoflagellates), increases in abundance in response to possibly precluding its tight association with species such reduced predation by Calanus spp. when the latter recede as capelin, which requires shallow (< 100 m) spawning from the surface layer (Fig. 14.13). After midsummer, habitats. Therefore, while model simulations indicate protozooplankton are the dominant grazer on the phyto- that warming will provide more suitable habitat for plankton community (e.g. Levinsen & Nielsen 2002). temperature-sensitive fish species such as the capelin, 516 Arctic Biodiversity Assessment

10 During the last decades, the open water period has extended significantly in Disko Bay. Sea ice coverage has ) -3 8 decreased by 50% while sea ice breakup (Hansen et al. 2006) and the spring bloom have occurred earlier. It is yll a m 6 unknown whether Calanus spp. can synchronize their ascent after winter hibernation to forage upon the earlier 4 phytoplanton bloom (Hansen et al. 2003). A mismatch between these events will result in insufficient food (mg chloroph 2 Phytoplankton biomass quality and thus low reproductive success for the cope- 0 pods (Madsen et al. 2001, 2008b, Hansen et al. 2003), thereby reducing the large reservoir of lipids accumu- 8 lated within successful copepod populations (Fig. 14.14). Any reduction of this key lipid resource will impact the 6 transfer of lipids through the rest of the food web. ) -2 Disko Bay is roughly the northern boundary for the 4 reproduction of the Atlantic Calanus finmarchicus and the (g C m southern boundary for C. glacialis (Madsen et al. 2001). opepods biomass

C 2 The two Calanus species differ in their life cycle, reproduction strategy and lipid content and may therefore re-

0 spond differently to climate change. C. glacialis initiates spawning prior to the spring bloom with gonad matura- 2.0 tion and egg production fueled by internal lipid reserves, most likely an adaptation to the unpredictable food con-

1.5 ditions in the Arctic environment (Conover & Huntley 1991, Falk-Petersen et al. 2009). C. finmarchicuson the ) -2 other hand, is generally dependent on foraging in order 1.0 to complete gonad maturation and initiate spawning due (g C m to smaller lipid reserves (Plourde & Runge 1993). 0.5 otozooplankton biomass

Pr Major changes in the Calanus community have been observed along W Greenland over the last decades. In the 0 AMJJASONDJFMAMJ early 1990s, the three Calanus species (C. finmarchicus, C. 19961997 glacialis and C. hyperboreus) each contributed one third of the copepod biomass in Disko bay (Madsen et al. 2001). Figure 14.13. Seasonal succession of ice cover, phytoplankton, However, recent investigations show that the Atlantic copepods and protozooplankton (ciliates and dinoflagellates) in C. finmarchicus now contributes 75% while the lipid-rich Disko Bay, W Greenland, 1996-1997. Sea ice cover is represented in Arctic species, C. glacialis and C. hyperboreus, contribute light blue. The vertical dark blue line indicates the time when the the rest (Madsen et al. 2008b), indicating a future trend bulk of Calanus spp. biomass leaves the surface layer giving room towards a much less lipid-rich food web. for an additional peak in protozooplankton biomass. (Modified from Madsen et al. 2001 and Levinsen et al. 2000).

Figure 14.14. Conceptual model of seasonal plankton succession in W Greenland in a) current and b) future warming conditions. Blue arrows indicate sedimentation of organic material. Under warming conditions (b), an increase in primary production and in the flux of organic material to the benthos and the protozooplankton community is expected. (Adapted from Rysgaard & Glud 2007).

ice-free period ice-free period Primary production Copepods biomass Protozoo- plankton

a) b) Chapter 14 • Marine Ecosystems 517

14.6. CONCLUSIONS AND northward. In regions isolated from advection of boreal waters, such as the Canadian Arctic Archipelago, changes RECOMMENDATIONS in biodiversity may be slower and mainly influenced by local changes. Trans-Arctic migrations from the Pacific 14.6.1. Vulnerabilities, adaptation and to the Atlantic Ocean are likely to occur increasingly, as looking forward Arctic sea ice continues to melt and could cause restruc- turing of marine food webs. The presence of the Pacific As primary production fuels marine food webs through diatom Neodenticula seminae in the North Atlantic Ocean its transfer to pelagic and benthic organisms, regional in the late 1990s after > 800,000 years of absence, was increases in primary production may be expected to attributed to increased transport of Pacific waters through augment the production of fish and shellfish species, the Canadian Arctic Archipelago (Reid et al. 2007). Such some of which have commercial value. Recent increases trans-Arctic expansions are likely to continue, reflecting in primary production associated with changes in sea ice the influence of the Arctic on global marine biodiversity. cover on two geographically opposed shelves, the Beau- fort and Laptev shelves, have been linked to observed/ Some unique habitats, species and elements of Arctic modeled increases in the sedimentation of organic mate- marine ecosystems are particularly vulnerable to on- rial (Lalande et al. 2009, Lavoie et al. 2009). In addition, going changes. The unique habitats associated with Arctic studies from Arctic areas (Svalbard) suggest that benthic ice shelves that have evolved over thousands of years are biota respond to fluctuations in regional climate patterns eroding and may be irrevocably lost in the current and (Beuchel et al. 2006). Enhanced environmental forcing predicted future climate. Multi-year ice and its associated leading to warmer winters with less sea ice, earlier onset habitats are at risk of vanishing, with major but largely of melting and increased precipitation in Kongsfjorden unknown direct and indirect effects on Arctic marine during the decade 1993-2004 (Svendsen et al. 2002) may ecosystem architecture. Ice-associated biodiversity is at have benefited the brown algae Desmarestia sp. due to the risk, with species such as the polar bear exemplifying increased availability of light and nutrients (Beuchel & climate-related impacts on Arctic marine biodiversity. Gulliksen 2008). These results point to changes in marine ecosystem architecture and biodiversity on Arctic As changes are occurring in the Arctic, marine species shelves, where sea ice cover is in a state of transition. and Arctic residents need to adapt. Hence, much local human transport that hitherto has taken place over ice may At the same time, recent studies indicate that the in- now use ships and boats for most of the year, and hunting creased freshwater content in the Arctic Ocean, through techniques developed for hunting on ice may be replaced the effect of stratification on plankton community struc- by open water hunting methods. Traditional ways may ture (Li et al. 2009), decreases the efficiency of transfer have to evolve, as expressed by this Inuit hunter: of organic material in Arctic marine food webs (Kirch- man et al. 2009, Cai et al. 2010). Therefore, an increase A buddy of mine is into making little sleds out of aluminum, in overall production in the Arctic Ocean may not neces- » which you can use as a little kayak or boat. If you’re out on sarily lead to more abundant harvestable species, as the the ice and you have to cross an open lead you can use that. It’s composition of communities largely determines the fate one of the things that can help. I’m going to get one of those. It’s of material in marine systems. Recent modelling also combined as a little sleigh and, if you have to, you can use it as a highlights the regional character of ecosystem responses boat. That’s one way I can adapt. to climatic forcing (Slagstad et al. 2011). (ICC 2008). The response of Arctic marine ecosystems to on-going Species with more plasticity are likely to better adapt to changes depends on complex interactions between com- a variable and changing environment than species with munity structure, trophic interactions, species-specific narrow tolerances and strict physiology or life history. adaptation and fitness in regard to environmental condi- For example, copepods and krill in the Barents Sea MIZ tions, superimposed upon anthropogenic stressors that show marked trophic plasticity, shifting from herbivory often have a strong local influence. The cumulative effects during the bloom to omnivory when fresh material is less of the thinning of the ice pack, its enhanced export in abundant. Predator fishes such as Atlantic cod also show relation to atmospheric circulation patterns, and warmer high feeding plasticity, shifting their prey from fishes to ocean temperatures may continue to alter Arctic sea ice zooplankton in response to changes in abundance. Such and associated ecosystems dramatically. How these and flexibility in feeding strategies may provide an advan- other emergent environmental and anthropogenic forcings tage in highly variable environments such as the MIZ will affect ecosystem biodiversity in the marine Arctic, (Tamelander et al. 2008). Phenotypic plasticity is also and in downstream marine systems, is unknown. expected to dominate responses of marine mammals to climate change in the short term (Gilg et al. 2012). Ac- Patterns of changing diversity will likely depend on cordingly, biodiversity can offer functional redundancy regional characteristics and habitat types, but also on the and increase the resilience of marine systems to multiple connectivity of ocean areas with boreal/southern regions. stressors. However, this resilience ultimately depends on In areas connected to boreal waters, increases in advec- the response of each species to individual and combined tion can result in the transport of more sub-Arctic species stressors and the resulting trophic interactions. 518 Arctic Biodiversity Assessment

Since the Arctic is at the northern limit of distribution forts. We also need to better understand the ecophysiol- of many species, northward range extensions due to a ogy of key species to be able to better parameterize bulk warming climate are likely to shift the balance of species processes and rates. as the sub-Arctic biome takes over the present Arctic and true Arctic species are pushed northwards or go extinct. For example, the mismatch of formerly synchronized Such changes, as exemplified by shifts in top predator reproductive events and the impact of altered food qual- species in Hudson Bay (i.e. killer whales versus polar bears, ity for herbivores under climate warming are not fully see Section 14.5.4), will affect ecosystem functioning and understood. Similarly, the effects of ocean acidification transfer pathways. In addition, extensive alterations in the on benthic and planktonic communities are in general physical and biogeochemical structure of Arctic marine poorly understood. Therefore, we need to gain knowl- ecosystems are currently taking place, with unknown edge on the responses of individual species and com- consequences for these ecosystems and the species that munities to elevated CO2 and on underlying mechanisms inhabit them. We cannot predict the tradeoffs between and possible acclimation processes. Furthermore, we the potential loss of unique ecosystems such as ice shelves need to study the interactive effects with other environ- and the introduction of new species via northwards range mental variables in order to predict the consequences for extensions and modifications in habitats. Arctic marine ecosystems. Much can be learned from studying and comparing spatial variation in the present- 14.6.2. Knowledge gaps and challenges day pelagic ecosystems along climatic, latitudinal or vertical gradients, and in linking the present with past. One of the greatest impediments to understanding the ongoing changes in the biodiversity of Arctic marine We still have a limited inventory and understanding of ecosystems is the fragmented nature of much of the ex- the current status of Arctic marine biodiversity, and isting knowledge and the lack of consistent and regular particularly so for the small microbial communities and long-term monitoring programs in most Arctic marine benthic invertebrates. There is still much to learn about regions, including unique or vulnerable ecosystems. the biodiversity of extreme habitats and organisms in A commitment to long-term studies is essential in this the Arctic. For example, there is recent evidence of the regard, and the establishment of the Arctic Marine Bio- widespread occurrence of cold seeps in the marine Arc- diversity Monitoring Plan supported by CAFF (Gill et al. tic, but the organisms inhabiting these unique habitats 2011) is an important step towards this goal. are poorly described. Similarly, unique habitats associated with sea ice and ice shelves are poorly understood The effects of disturbances and stressors on Arctic and their biodiversity is largely unknown. This special marine biodiversity are not well understood. The lack biodiversity in the Arctic presents opportunities for ad- of baseline information in many areas, the wide range vancements in biotechnology, medical research and even of ecosystems and the impact of cumulative effects the search for life on other planets. Deep basins of the make it difficult to predict the direction of changes. Arctic Ocean, which were largely inaccessible, are be- The multiple stressors currently affecting Arctic marine coming ice-free in summer, bringing new opportunities ecosystems operate simultaneously at various temporal for research and exploration. As one of the last frontiers and spatial scales, emphasizing the need for local and on Earth, the marine Arctic still holds many discoveries concerted biodiversity assessment and monitoring. There with respect to the biodiversity of its ecosystems and the is also a need to develop indicators that properly reflect species that inhabit them. the unique characteristics of Arctic marine ecosystems. For example, habitat fragmentation, used as a global 14.6.3. Key points and recommended actions biodiversity indicator, could be characterized in the marine Arctic using a variety or combination of indica- The marine Arctic spans a wide range of environmental tors including sea ice extent and water mass distribution conditions including extremes in temperature, salinity, indices. These physical/chemical indicators could then light conditions and the presence (or absence) of sea ice, serve as structuring elements upon which to moni- leading to diverse Arctic marine ecosystems. These eco- tor associated ecosystem biodiversity trends. Shifts in systems are experiencing rapid changes in their chemi- ecosystem structure, species interactions and trophic cal, physical and biological characteristics together with pathways need to be understood in the context of short- unprecedented socio-economic pressures. Changes in the and long-term trends, in order to develop management distribution and abundance of key species and cascading strategies to maintain the diversity and sustainability of effects on species interactions and the structure and func- Arctic marine ecosystems. To this effect, it is essential to tionality of marine food webs are already observed. include biological elements in monitoring programs for the marine Arctic. Range extensions are taking place throughout the Arc- tic, with a northward expansion of sub-Arctic species To gain new knowledge and make sensible projections and a narrowing of Arctic habitats that have existed over about climate impacts on carbon dynamics and seques- millions of years such as multi-year ice and ice shelves. tering in Arctic marine ecosystems, key organisms from Under current climate scenarios, the loss of these unique the base of marine food webs need to be considered, ecosystems could be irreversible. parameterized and included in research and modeling ef- Chapter 14 • Marine Ecosystems 519

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