This paper was written as part of the 2010 Alaska Oceans Sciences Bowl high school competition. The conclusions in this report are solely those of the student authors.
Impacts of climate change on sea ice and Bering Sea primary production
The multiyear sea ice retreat in the Arctic Ocean and Bering Sea is due to a changing climate and a warming world. Annual mean ice extent has decreased by 2% during the past 25 years. This reduction is a self-renewing cycle, due to ice-albedo feedback, and will have ramifications on all parts of the ecosystem. Spring phytoplankton blooms occur in the wake of retreating sea ice, often in vertically stable water. Ice melt increases this stability as it decreases mixing. This lessens influxes of new nutrients and can lead to nutrient-limited blooms. Since phytoplankton are the base of the trophic web, any change in blooms and concomitant zooplankton abundance will impact many species. We explore in particular expected effects on walleye pollock (Theragra chalcogramma), harvested in Alaska's largest commercial fishery, and on bowhead whales (Balaena mysticetus), relied on for subsistence in many rural communities. Although it is likely that adult pollock biomass will increase briefly, overall biomass will then decrease. We show that changes in the food web resulting from climate change will affect these species and pose economic and other hardships on Alaskans. We conclude that ongoing monitoring and research of Being Sea productivity and conditions must be made a high priority, so as to understand and create a baseline from which to adapt to further changes. This is necessary both to conserve species and to manage responsibly those species utilized commercially or for subsistence. We specifically suggest further research into the exact effects of stratification on primary production. We further conclude that the state must be ready to diversify its economy if a fisheries crash occurs. Towards this end, we propose and discuss the creation of a jellyfish fishery that would take advantage of the fact a jellyfish increase has already been seen in the Bering Sea and that jellyfish generally do well in warmer, more acidic waters.
Anthropogenic CO2 emissions from an expanding industrial world have contributed to an overall increase in global temperature, altered (terrestrial and marine) ecosystems and tropic webs, acidification of the worlds oceans, and a changing climate. Climate change occurs when the state of the climate quantitatively shifts and does not return to normal patterns within a few decades. The exact definition of climate change is not fully agreed upon; the United Nations Framework Convention on Climate Change specifies anthropogenic causes, while the definition of the Intergovernmental Panel on Climate Change does not have this qualification (IPCC, 2007).
Global climate change associated with carbon dioxide emissions is affecting the Arctic more dramatically than other regions (IPCC, 2007). The Arctic and Bering Sea are warming at a faster rate than the rest of the Northern Hemisphere. A leading repercussion of this is a loss of Arctic sea ice. During the last 25 years the annual mean ice extent has decreased by 2%, the ice area has decreased by 3% (Singarayer et al., 2006), and the average central Arctic sea ice thickness has been reduced (IPCC, 2007). Ice is melting at an accelerating rate because it has a higher albedo than seawater, and Arctic sea ice melting causes the newly exposed ocean to absorb more energy. This raises the temperature and creates a positive feedback loop (Curry et al., 1995). Current models predict that the Arctic Ocean will be predominantly ice-free in summer by the year 2037 (Wang and Overland, 2009) rather than 2100 (Smetacek and Nicol, 2005) as was initially predicted.
Sufficient nutrients are required for phytoplankton blooms to occur. Blooms also need sunlight and water column stability (stratification) to keep blooms in the photic zone (Garrison, 2007). In the wake of melting ice, stratification is increased by a greater density gradient, and by a thermocline in summer. However, in open water with no seasonal ice cover, stratification is primarily thermal. Without the ice's protection from wind, the water column becomes more mixed, and stratification is decreased.
As ice retreats, phytoplankton blooms are able to grow in the Bering Sea shelf domain. These blooms may continue until nitrate is depleted, since adequate iron is currently provided by sea ice (Aguilar-Islas et al., 2008). Spring phytoplankton blooms are associated with stratification of the water column due to ice melt (ice-associated blooms), or by absorbed solar radiation (open-water spring blooms) (Jin et al., 2006). When the winter ice retreats earlier in the spring (before mid-March) it results in an open-water bloom. Conversely, when the winter ice stays longer (mid-March or later), an ice-associated bloom commences (Hunt and Stabeno, 2002). The timing of the sea ice retreat in spring and cessation of winter storms appears to have an important effect on the timing of the spring phytoplankton bloom. An ice retreat that occurs prior to the cessation of strong wind-induced water mixing results in delayed open water spring blooms until solar heating has stratified the water column (Hunt and Stabeno, 2002). There is the potential for repeated mixing events and a prolonged bloom in the late spring. An ice retreat that occurs after storm cessation affords a density stratification of the water column allowing an ice-associated bloom to begin (Hunt et al., 2008). The timing of the spring bloom affects the production of zooplankton species such as Calanus copepodites that play a vital role in transferring energy captured in primary production into a form used by large planktivorous fish, cetaceans and sea birds (Hunt et al., 2008).
The Bering Sea ecosystem is mainly pelagic-based and is very sensitive to climatic changes and influences. This is apparent in unusual occurrences such as Pacific salmon returns far below predicted levels (Napp and Hunt, 2001), a high mortality of short-tailed shearwaters and an intense coccolithophore bloom (Stockwell et al., 2001). Retreating ice and the subsequent warming water will likely result in species shifting northward (Kurland, pers. comm.). These changes in species composition of the prey base and subsequent impacts on the food web culminate in impacts on species important to both commercial and subsistence fishing (Kruse, 1998). In 2008, Alaska led all states in volume and value of commercial fisheries harvested (Kurland, pers. comm.), and revenues from fisheries are the second largest contributor to the Alaska General Fund. Alaskans throughout the state rely on subsistence fishing, which provides an average of approximately 104 kg of food per person per year (Fall et al., 2009).
The Bering Sea is the most productive marine ecosystem in the United States. Any change to this ecosystem that causes a reduction in productivity, a change in species composition, or a change of the food web will have a severe societal impact. There is currently dispute as to the exact changes that will occur to species composition, timing, and location of blooms, as well as to nutrient availability and physical oceanographic features, but it is not disputed that changes will take place (Jin et al., 2006).
In this paper we discuss current nutrient cycling and expected changes relating to a loss of ice, physical aspects of the Bering Sea, and the effects thereof on phytoplankton production. We discuss the ramifications for higher trophic levels, and note expected impacts on Alaska's economy and people. Finally, we discuss strategies to deal with probable changes.
Phytoplankton in the Bering Sea
Phytoplankton productions is at the base of the food web, and vitally important to higher trophic levels. Primary production in the ocean is affected by light, advection, stratification, nutrient supply and vertical mixing (Springer et al., 1996), whereas secondary production is highly dependent on timing, magnitude, and quality of primary production and occurs when vertical stratification has developed.
The timing of the spring bloom affects various processes in the food web such as food availability, and distribution and abundance of predators. Strong stratification and limited nutrients in surface water in 2004 limited lower trophic level activity on the shelf (Strom and Fredrickson, 2008). The most productive area in the Bering Sea is the Green Belt. This is associated with the upwelling of nutrient-rich water entrained in the Bering Slope Current, which, after flowing along the shelf break, is then enriched by the Anadyr Current (Loeng et al., 2005). Greenbelt phytoplankton blooms occur in spring and are sustained by nutrient inputs into the late summer (Springer, 1996).
Bering Sea ecosystem shifts are being magnified and complicated by ice-associated blooms seeded by sea ice algae. Ice algae have little impact on total annual productivity but significant impact on species composition shifts and the timing and magnitude of the phytoplankton blooms. Differences in composition and/or magnitude of sea ice algae may cause changes in the suitability of spring blooms for zooplankton grazing (Strom and Fredrickson, 2008). These organisms are the link between primary production and higher trophic levels. Ice-associated blooms are sensitive to short-term changes as well as to long-term climate changes. A shift from a cold to a warm regime in 1976–1977 caused the phytoplankton biomass to peak later in the year than the cold years (Jin et al., 2007). This change may cause the whole food web to shift from bottom-up control (primary production controlling species populations) in cold regimes to top-down control (predators controlling populations) in warm regimes.
Warm, low nutrient waters have been thought to favor coccolithophore blooms which reduce larger zooplankton grazing and trophic transfer. The first large-scale coccolithophore bloom in 1997 was associated with major ecosystem changes including an increase of small copepods, altered euphausiid production, and high mortality of short-tailed shearwaters (Strom and Fredrickson, 2008).
Under-ice blooms increase for the duration of ice cover, and stabilize when the ice retreats. Ice-edge blooms, on the other hand, occur in spring when ice melts back leaving a nutrient-rich surface layer that may assist the rapid increase of chlorophyll via ice algae left behind. These blooms produce a large fraction of the total primary production on the shelf immediately following ice retreat, but contribute little after the water becomes highly stratified.
Strom and Fredrickson (2008) found that high chlorophyll levels were usually associated with large-cell-dominated phytoplankton that grew at higher rates when nutrients were not limited. The Pribilof Canyon area is not largely impacted by nutrient limitation because the transport of nutrients onto the slope and outer shelf is adequate at that location (Strom and Fredrickson, 2008). Total grazing rates were low for the entire summer of 2004, a relatively warm year in which phytoplankton grew at a fraction of their maximum physiological rate. Grazing-to-growth-rate ratios were reduced in 2004 compared to 1999 (a cold year) almost by half, possibly reducing availability of prey for zooplankton, birds and mammals higher in the food web (Strom and Fredrickson, 2008).
Physical oceanographic aspects of the Bering Sea
Physical factors including salinity, stratification, mixing, and currents dictate the abundance, size, timing, distribution, and concentration of phytoplankton (Loeng et al., 2005). The Bering Sea may be more sensitive to decadal variability than to long term variability since it is connected to two major climate modes, the Pacific Decadal Oscillation and the Arctic Oscillation.
Historically, sea ice has extended to the outer shelf with maximum ice extent in late-March (Aguilar-Islas et al., 2008). Early models predicted that the summer Arctic Ocean would be ice free by the end of the century (Singarayer et al., 2006; Smetacek and Nicol, 2005), however, more recent models predict an ice free Arctic by 2037 (Wang and Overland, 2009).
On a larger scale, atmospheric cells, wind patterns, and current patterns in the Arctic and Bering Sea are changing because of sea ice melting and climate change; for example, there has been an recent increase in tropical storms arriving in the Bering Sea. The current prevailing winds in the Arctic are northeasterly and since phytoplankton are drifters, changing wind patterns and associated currents may alter their geographical distribution. However, exactly how winds and currents may change is not completely understood (Curtis, pers. comm.).
Bering Sea nutrients overview
Nutrients are necessary to promote and sustain phytoplankton blooms (Garrison, 2007). In brief, phytoplankton blooms are dependent on macronutrients (fixed N, P, and Si), which are often limiting, and a host of micronutrients, of which Fe or Mn may be limiting (Millero, 2006). Currently, seasonal melting sea ice increases stratification and dampens summer vertical mixing. This stable water column creates ideal conditions for ice-edge phytoplankton blooms, but once nutrients are depleted the stability prevents nutrient-rich upwelling (Aguilar-Islas et al., 2008). However, summer storms may mix the water column and initiate a secondary bloom (Jin et al., 2006). Once sea ice is permanently absent, the de-stratification will cause increased vertical mixing, nutrient availability, and a possible increase in primary production. However, production may become light-limited due to low water column stability. Prior to this, while the multi-year ice melt is occurring, fresh water stratification will result in nutrient depletion.
Nutrients on the shelf
The Bering Sea shelf has been divided into three domains (coastal, middle, and outer) that are typified by different nutrient regimes but that become depleted of nutrients by spring blooms (Sambrotto et al., 2008; Tanaka et al., 2004). These domains are separated from the deep basin (oceanic region) by the shelf break and from each other by distinct frontal areas, which are transition zones between water masses of different density and characteristics. The oceanic region is associated with high summer primary production; in contrast, the shelf is subject to blooms lasting less than one month (Sambrotto et al., 2008). The coastal domain is well mixed, becomes nutrient depleted, and is nitrogen-limited (Tanaka et al., 2004). The middle and outer domains consist of a warm, wind-mixed layer on the surface and a bottom tide-mixed colder layer.
The outer shelf has large concentrations of macronutrients, and when the ice edge reaches it in spring, large phytoplankton blooms occur until limited by dissolved iron (DFe) that appears to arrive from melting sea ice (Aguilar-Islas et al., 2008), and from sediments, river input, and aeolian deposition (Aguilar-Islas et al. 2007). The idea of sea ice-introduced DFe was supported by Lannuzel et al. (2008), who showed a decrease of DFe in pack ice in the western Weddell Sea resulted in an increase of DFe in the adjacent water column.
The Bering Sea has three highly productive areas, one associated with modified Bering Shelf water, and the second extending north of St. Lawrence Island to the Chukchi Sea. The third productive area is the Green Belt, located along the shelf break (Hansell and Goering, 1990). Aguilar-Islas et al. (2007) showed that although sufficient micronutrients are present in the region to support productivity, they do not appear in a high enough concentration for complete macronutrient drawdown. They also showed that diatoms in the Green Belt absorb relatively more silicic acid than nitrate, indicating that these diatoms are iron limited. If iron is no longer added by yearly ice melt, this iron limitation may become more severe, and further limit growth.
Expected changes in nutrient availability
If sea ice extent continues to decrease the effects on nutrient availability in the Bering Sea may be pronounced. Aguilar-Islas et al. (2008) suggest that in years without sea ice there will not be enough DFe present in the water column for phytoplankton blooms to remain at their current levels. It can be expected that spring bloom timing and composition will change. However, more research is needed before the full influence on blooms of both ice-introduced DFe and its absence are understood.
Phytoplankton blooms may decrease with ice retreat as sedimentary denitrification on the shelf results in nitrate deficiency. Anoxic conditions in the sediments result in reduction of nitrate. This causes a concentration difference across the sediment-water interface that results in nitrate depletion in the water above. Denitrification has been seen on half the shelf (Tanaka et al., 2004) and increases with temperature. Abnormally high bottom temperatures such as those in 2003 could lead to lowered production in the middle and coastal shelf during summer and fall, as upwelled water would be nitrate deficient (Aguilar-Islas et al., 2007).
During the 1997 El Niño/Southern Oscillation event, when southerly sea ice extent occurred late and spring ice retreated rapidly, the nitrate uptake and phytoplankton growth were greater below the pycnocline than at the surface. This led to low nitrate concentrations in bottom water, that, with unusually warm water, may have contributed to unusual plankton blooms. That year, primary production was significantly higher than previous norms (Stockwell et al., 2001). These warm conditions may provide insight into recent shifts to warm water regimes caused by lack of residual cold ice melt.
Zooplankton are sensitive to the timing of primary production in the Bering Sea. In colder years phytoplankton are not grazed as much as in warmer years, allowing them to sink to the benthic communities. However, in warmer years, phytoplankton bloom later in stratified, warmer water (Jin et al., 2009).
Zooplankton biomass and growth rate are positively correlated to chlorophyll levels, which indicate phytoplankton density. Highly stratified waters with low nutrient renewal rates may result in food limited early-stages of larvae and copepods (Loeng et al., 2005). A shift in the species and size composition from large zooplankton to smaller copepods occurred between 1999 and 2004 in conjunction with warmer surface temperatures. Coyle et al. (2008) hypothesized that the stability of the water-column and warmer temperatures might have reduced primary production and made species more tolerant of warm, oligotrophic waters thrive. Calanus marshallae historically have been the dominant grazer in the Bering Sea since at least the mid-1990s, and dense patches are directly related to the presence of foraging baleen whales. Euphausiids are also common and are important components in diets of fish, birds and mammals, but are appearing in lower concentrations in recent years; this may indicate a change in distribution and abundance in the southeastern Bering Sea. Such a change would likely affect fish, birds, and mammals that forage on the euphausiids (Coyle et al., 2008).
Higher trophic levels
Impacts from changed phytoplankton productivity to organisms at higher trophic levels have been observed recently. Examples include reduced shrimp and forage fish and poor recruitment of pollock (Theragra chalcogramma) and Pacific cod (Gadus macrocephalus) (Mueter et al., 2009). Pollock biomass increased after 1978, but now appears to be decreasing (http://www.cf.adfg.state.ak.us/geninfo/finfish/grndfish/pollock/pollockhome.php). Between 2001 and 2005, when there was very little ice cover, the recruitment of pollock in the Bering Sea was below average (Mueter et al., 2009). Adult pollock are an important intermediate predator in the Bering Sea, and juveniles are a forage group that provides an important food source for sea birds, marine mammals and groundfish (Winter et al., 2004). Hunt and Stabeno (2002) suggest that the early ice retreat years result in warmer water conditions that may favor pollock growth and recruitment because in colder years phytoplankton blooming in unstratified waters are less grazed and sink to the bottom, benefiting benthic communities (Mueter et al., 2007). In contrast, blooms in warmer stratified water benefits the pelagic community (Hunt and Stabeno, 2002), including pollock (Mueter et al., 2007). However, an increase in the adult biomass means a decrease in juvenile pollock biomass since adult pollock in the Bering Sea are cannibalistic and so are responsible for most juvenile pollock mortality. Therefore even if conditions become more favorable for phytoplankton and adult pollock, there will be a gradual decrease in the pollock biomass over time (Aydin and Meuter, 2007).
Pollock also suffer from reduced visibility and foraging ability associated with large phytoplankton blooms cause by early ice retreat. This was shown by a large coccolithophore bloom in 1997 (Winter et al., 2004).
Flatfish in the Bering Sea that consume mostly infaunal prey such as polychaetes, clams and echiuran worms (Loeng et al., 2005) are another group of fishes that may be impacted. Since 1980, many species of flatfish have been declining, possibly reflecting changes in the Bering Sea ecosystem. These changes include altered migration pathways and areas of altered benthic production (Spencer, 2008). Atheresthes stomias biomass appears to be affected by the Bering Sea cold pool (the cold water remnant of ice melt) (Spencer, 2008), and changes to this cold pool are likely to affect their biomass. Fish distributions may also move north in response to changes, as the Arctic pelagic-based ecosystem moves into the currently benthic-dominated Arctic Ocean (Kurland, pers. comm.)
Bowhead whales (Balaena mysticetus) are mammals closely associated with the Arctic sea ice. They feed mainly on Euphausiids ranging from 3 to 30 mm, copepods, and other epibenthic organisms in the Bering Sea (Sheldon et al., 2001), which are likely to be affected as well. Bowheads are traditionally hunted by Alaska Natives for subsistence as they pass St. Lawrence Island during their migration north. The timing of the spring migration has changed from April and May, to March. Additionally, in years when there is an early ice retreat there has been a decline in Bering Sea bowhead whale population (Taylor, 2003). Studies indicate that populations were lower during the climate optimum at the end of the last ice age approximately 8500 years ago when the Arctic ice extent was considerably smaller than it is now. From this, researchers infer that an early Bering Sea ice retreat could cause the bowhead whale population to decline (Taylor, 2003).
Steller sea lions (Eumetopias jubatus) are endangered in some places and climate changes may decrease the likelihood of their recovery. Since the mid-1970s, researchers have observed a decrease in other pinnipeds, as well. Merrick et al. (1997) observed a direct correlation between diet diversity and sea lion population size. The stomachs of sea lions have been found to contain relatively more walleye pollock than nutrient rich forage fish, such as Pacific herring (Clupea pallasi) (Aydin and Meuter, 2007). Merrick et al. (1997) suggest that due to foraging efficiency, a diverse diet is superior to a specialized one. There are significant energy deficiencies associated with consuming pollock; captive Steller sea lions on a pollock-only diet showed metabolic depression and lost weight due to the low calorie density of their food.
Climate change in the Bering Sea will also affect piscivorous seabird populations (Loeng et al., 2005). Over 60 species of seabird species migrate through the Arctic and over 40 species breed there. Many species migrate to the Arctic in the summer during the area's peak productivity. The Pribilof Islands are the main breeding spot in the Bering Sea for piscivorous seabirds (Loeng et al., 2005). Most forage for small fish and copepods in mid-water column in frontal areas or at ice edges where there are high concentrations of marine zooplankton (Loeng et al., 2005). Changes in seabird distribution patterns will occur because the retreating ice pack will open up more feeding areas in the spring. Seabirds are going to be greatly influenced by shifts in prey availability and distribution in the Bering Sea (Loeng et al., 2005), with increased energetic stress possibly reflected in higher adult post-breeding mortality.
It is important to recognize that the ecosystem as a whole is likely to change. In any situation where the general ecology is altered, some species fair better than others, and not all species that fair well are beneficial to humans. An example is jellyfish. Over the last few decades, the Bering Sea has seen an increase in jellyfish populations (Brodeur et al., 2002). Jellyfish favor warm, acidic water, and thus can be expected to thrive in an ice-free Bering Sea, because as sea ice melts, the atmosphere-water interface where dissolution of carbon dioxide occurs is correspondingly larger. Thus, it would be expected that as ice melt occurs earlier and ice retreats, the potential amount of carbon dioxide dissolution is greater. This will raise ocean pH through the well-understood process of ocean acidification. This increase in jellyfish is already occurring. Michelle Ridgway (pers. comm.) reported that during a recent submarine dive, her vessel was surrounded by more jellyfish than she had before seen, and that one of them was digesting three herring and various zooplankton.
However, neither this population increase nor its causes have been adequately assessed. While the trophic relationships between jellyfish and fish in the Bering Sea are not well known, the sudden increase in biomass of jellyfish may have ecological impacts. The diet of Chysaora melanaster, the most abundant species of jellyfish in the southern Bering Sea, consists mainly of other medusae, crustaceous zooplankton, and juvenile pollock. A study done in 1999 around the Pribilof Islands estimated that C. melanaster was consuming around 2.8% of pollock stock per day in the month of July. Though that population has since decreased, jellyfish continue to compete with fish (Brodeur et al., 2002). The diet of jellyfish overlaps with that of many fish species. Jellyfish will be able to out-compete these fish populations for food because they have a higher consumption rate and can respond more rapidly to pulses of food than can their competitors. Additionally, larval fish are often prey items for jellyfish. Brodeur et al. (2002) suggested that environmental forcing due to climate change could be a driving factor in invasive jellyfish. The apparent success of jellyfish in the changing conditions of the Bering Sea is ominous because very little of the jellyfish biomass is passed on to higher trophic levels, thus limiting overall production in the marine ecosystem. They are a growing menace and are becoming a hindrance to fishing in the Bering Sea.
Impacts on commercial fisheries and subsistence
Fisheries comprise a major portion of the Alaskan economy and a large source of both state revenue and jobs. Multiple species are being utilized directly for subsistence. Seafood production is currently the second-largest industry, and the seafood workforce is the largest in the state. Alaska accounts for about half of the fisheries of the United States (Kurland, pers. comm.). The Alaska Department of Fish and Game and the National Marine Fisheries Service are, respectively, the preeminent state and federal fisheries management agencies (Woodby et al., 2005).
Currently, pollock are the number one product of Alaska fisheries (http://www.cf.adfg.state.ak.us/geninfo/finfish/grndfish/pollock/pollockhome.php) and comprise the largest seafood fishery in the U.S. A reduction in pollock biomass will have a dramatic impact on Alaskan fisheries and on communities that benefit from the Western Alaska Community Development Quota (CDQ) program that allocates a proportion of the profits of groundfish (including pollock) to communities in western rural Alaska. Sixty-five Bering Sea communities participate in the program, which has generated over $362 million. Thus, a reduced pollock production would damage communities. As environmental changes make the continued harvest of pollock more difficult, the desire to offset losses with an increase in area and type of harvest may become increasingly difficult to reconcile with regulations already in place to protect endangered marine mammals (notably the Endangered Species Act), by-catch of chinook salmon (Oncorhynchus tshawytscha) (http://www.cf.adfg.state.ak.us/geninfo/finfish/grndfish/pollock/pollockhome.php), or with as-of-yet undetermined alterations to the fishery associated with climate change.
Subsistence is vitally important to many Alaskans, and the case of the bowhead whale illustrates potential impacts on subsistence from melting sea ice. Twenty-five to forty bowhead whales are taken each year for subsistence purposes. While this does not significantly impact the bowhead whale population, it does constitute a significant source of subsistence material for the Alaska Native populations (http://www.adfg.state.ak.us/special/esa/whale_bowhead/bowhead_whale.php). Predicted decreases in the bowhead population will impose cultural and dietary changes on those dependent upon the whales.
It is important to recognize that these are not the only issues associated with ice melt that will affect the Bering Sea ecosystem and important fisheries. For example, ocean acidification is occurring more rapidly in the Bering Sea than in many other regions, and poses additional challenges for a multitude of organisms (Short, pers. comm.). Ocean acidification will make forming CaCO3 more difficult for calcifying organisms. Lowered pH will also decrease PO43- availability in water and shift the ratio of ammonium-to-ammonia, thus impacting all phytoplankton.
Conclusions and recommendations
The scientific community has now accepted that the Arctic sea ice is thinning and retreating (Singarayer et al., 2006). There is little we can do directly to slow down the retreat; however, we can and must drastically reduce our global emissions of CO2 by developing and using energy sources that do not result in carbon dioxide emissions such that further impacts are minimized. A variety of strategies to reduce emissions have been proposed (Edmonds et al., 2007) and comprehensive strategies to achieve a sustainable energy future were recently proposed by Jacobson and Delucchi (2009). Citizens of Alaska and of the world must come to recognize the immediacy of the problems facing the ocean and the sustainability of current fisheries. The problem can only be solved if governments (national, regional, and local) develop and impose regulations that are designed to reduce human impact and at the same time work with other entities to educate the public.
The need for further and intensified research in the Bering Sea and Arctic Ocean is clear, given the number of currently conflicting hypotheses about the fate of the ecosystems and species thereof. We believe that the effect of differing levels of stratification on phytoplankton needs to be further explored, so that a greater understanding of primary production during multiyear ice retreat can be reached. The physical, biogeochemical, and biological components also need long term monitoring and research in order to adapt policy and strategies designed to maintain sustainable fisheries, species, and ecosystem diversity, and to develop a baseline from which further comparisons can be made. This is especially true since there is evidence that ecosystem responses to severe pressures are often sudden and nonlinear. If a regime shift is indeed on its way, we must be all the more vigilant. We feel that the shortened ice period and concomitant warm water of the 1997 El Niño/Southern Oscillation year may provide insight into the current sea ice melting trend. Additionally, since it has been shown that ice-albedo feedback from ice melt increases surface temperature (Curry et al., 1995), and that increased temperature speeds sedimentary denitrification (Aguilar-Islas et al., 2007), we conclude that continued ice melt will lead to reduced nitrate concentrations in the Bering Sea.
Whatever the ultimate effects on phytoplankton from retreating Arctic ice, climate change and ice retreat will cause a shift in species in Alaskan waters. Fisheries the state has relied on in the past will change. Commercial fisheries and rural communities must be prepared to adjust (Kurland, pers. comm.).
The expanding jellyfish population represents an opportunity and a possible mitigating economic factor for Alaskan fisheries for the expected declines in pollock stock. The creation and development of an Alaskan jellyfish fishery to boost Alaska's economy would also reduce the high numbers of jellyfish (an organism expected to do well in more acidic waters) in Alaskan waters. Edible jellyfish have been used as food in China for over a thousand years, and semidried jellyfish are a multimillion dollar industry in many Asian countries, with at least 12 species being harvested currently (Hsieh et al., 2001). In recent years, Japan alone has imported 4899–9072 metric tons of jellyfish products (http://www.trade-seafood.com/species/jelly-fish.htm). These are valued at approximately $25.5 million. Jellyfish processing consists of soaking jellyfish in salt and alum (Hsieh et al., 2001). Jellyfish fisheries exist in Thailand, (Crawford, 2006), and have been approved in several parts of Australia (http://www.environment.gov.au/coasts/fisheries/qld/jellyfish/index.html). Investigations into the feasibility of Alaskan jellyfish harvesting and processing should be conducted.
Although there is debate as to the exact effects of melting sea ice on phytoplankton, all papers we reviewed offered the perspective that change is occurring, and will continue. The impact of sea ice melt on phytoplankton productivity coupled with added complications of ocean acidification are not fully quantified. However, we conclude that species composition, bloom timing, and availability of phytoplankton to higher trophic levels are certainly going to change. This may lead to ripple effects, altering species abundance and species composition in the Bering Sea in an unpredictable manner. Changes will affect Alaska's existing commercial fisheries, and will also impact Alaska's rural people through changes in subsistence species such as bowhead whales. Measures must be adopted and implemented to regulate and protect Alaska's fisheries. Moreover, policy decisions must be made for the communities which can no longer rely on their traditional lifestyle. One possible solution would be to utilize salmon incidentally caught in the pollock fishery to supplement subsistence harvests for these populations. While this measure raises questions about by-catch storage and transport, energy consumption, and cultural appropriateness, it is representative of the creative solutions that will be needed if we are to help those affected by the large ecosystem shifts of our time. Human ingenuity is being put to the test, and the people of Alaska and the world must rise to the occasion.
We would like to thank Michelle Ridgway, Jeff Short, Clay Good, Jim Hale, and Steve Lewis, for editing our paper. We would also like to thank Terry Whitledge, Lisa Eisner, Jon Kurland, John Eiler, Rolf Gradinger, Lisa Matlock, Phil Rigby, Bonita Nelson, Tom Ainsworth, Peggy Sullivan, and Joel Curtis for their gracious assistance.
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