The eastern Bering Sea is a highly productive marine ecosystem, supporting more than 40 percent of the annual commercial fisheries landings by volume in the United States. Scientists have developed new models that predict more extreme changes in this ecosystem by the end of the century. They anticipate larger summer northward shifts and changes (both increases and decreases) in the area occupied by important commercial crab and fish species.
Specifically, the majority of models estimate changes in the center of distribution for several commercially important species. They predict that most species’ summer distributions will shift north by between 50 and 200 kilometers by 2080-2089. Scientists also project:
- Large declines in the amount of area occupied by red king crab and snow crab and potentially northern rock sole in the summer months.
- A substantial increase in the area occupied by arrowtooth flounder, a key predator of walleye pollock.
- Declines in probability of occurrence for most species in areas with low pH and oxygen concentration.
These changes are altogether more extreme than previous species distribution model projections, which accounted for fewer climate effects.
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Maps of two metrics of environmental novelty in the Bering Sea survey region for average temperature, pH, and oxygen conditions during 2040-2059 and 2080-2099, under each climate scenario (SSP 1-2.6 & SSP 5-8.5) and ESM (CESM, GFDL, & MIROC). Areas in gray are those for which temperature, pH, and oxygen are within the range of the average hindcasted conditions between 1995 and 2015. Areas in red / orange are those for which temperature, pH, and/or oxygen lie completely outside of the set of average conditions observed between 1995 and 2015. Areas in blue / green are those for which temperature, pH, and oxygen lie inside the range of hindcasted conditions, but represent novel combinations of these covariates. For both metrics, brighter colors indicate more novel conditions.
New and Better Models to Anticipate Ocean Changes
Scientists built species distribution models for eight common and/or commercially important species of groundfish and crabs in the eastern Bering Sea (adults and juveniles). These include walleye pollock, Pacific halibut, Pacific cod, arrowtooth flounder, northern rock sole, yellowfin sole, snow crab, and red king crab.
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To date, most studies projecting marine species distributions rely principally on temperature and static habitat characteristics such as depth. This can potentially lead to significant underestimation of species vulnerability to climate change.
However, for this study, ecologists combined 40 years of scientific surveys with a high-resolution oceanographic model. This model was adapted to the eastern Bering Sea by scientists at NOAA’s Alaska Fisheries Science Center as part of the Alaska Climate Integrated Modeling project. They examined the effects of bottom temperature. But they also incorporated information on oxygen, pH, and a regional climate index (the extent of the eastern Bering Sea “cold pool”). They considered all of these factors to produce a range of different climate projections through the end of the century. Model projections also anticipated warming under both low and high greenhouse gas emission scenarios.
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Oxygen and pH
The oceans absorb about 30 percent of global carbon dioxide emissions, and warmer water holds less oxygen. Climate change is also leading to the acidification of deoxygenation of much of the global ocean. All animals need oxygen to survive, and many species are expected to shift towards deeper, cooler waters to keep up with climate change. Lower dissolved oxygen content at depth may constrain their ability to do so. Reduced pH in water has the potential to impair organisms by changing their metabolism and physiological function. For crabs and other calcifying organisms, it can decrease calcification and shell formation rates.
Yet, few studies projecting future changes in species distributions integrate the effects of oxygen and pH. In many cases, these variables are not available to modelers, but recent advances in oceanographic modeling have made it possible to include their effects.
The authors found that the estimated effects of oxygen and pH were largely consistent among species. Where environmental oxygen and pH levels were lower, groundfish and crabs were less likely to be observed in scientific surveys. However, they also found the effects of oxygen and pH were difficult to disentangle using survey data, so they modeled their effects using separate models. In projecting future climate-driven changes in species distributions, they gave more say to models that did a better job reproducing past trends.
Where Scientists Hope to Go Next with this Research
These results build on—and in many cases agree with—previous distribution modeling efforts in the Bering Sea. However, they demonstrate that models that account for factors beyond temperature can result in more pronounced range shift projections.
“What’s really exciting about this research is we are now able to construct long-term species range forecasts, which incorporate a wider array of climate impacts,” said Kirstin Holsman, co-author and research fishery biologist, Alaska Fisheries Science Center.
In future work, species distribution models may be used to improve the representation of species interactions in multispecies stock assessment models. Scientists also hope to be able to produce short-term forecasts and long-term projections that incorporate a better understanding of predator-prey overlap.
Alaska Fisheries Science Center, NOAA Fisheries, 17 December 2024. Press Release.
