The activities of a diverse array of large apex predators of Beringia—the combined coastal shelves of the Bering, Chukchi, Beaufort, and East Siberian seas—initiate cascading effects on nutrient cycling and ecosystem processes. Sea ice has been a defining factor for the habitats of large populations of five species of ice-dependent seals and walruses that partition Beringian environments and affect those environments in different ways. Sea ice is presently diminishing at an accelerating rate, dramatically changing the habitats and behavior of those species. Insight may be gained through examination of the Pacific walrus (Odobenus rosmarus divergens), a very large, formerly abundant, relatively well-known, benthic consumer. Walruses had formerly depended on configurations of the sea-ice seascape for reproduction, feeding, transport, and rest. However, sea-ice diminishment has now caused the walrus population to alter former behavioral patterns in both time and space. Two fundamental questions arise; first, how may the natural histories of ice-dependent species affect ecosystem processes and, second, may the diminishment of those species affect ecosystem resilience at regional scales? Changes in sea ice structure (2010-2017) and natural history theory provide the basis for analysis.
Results/Conclusions
Walrus consumption represents a classic case of how top-down, patchy, ecological pulsing may affect nutrient transfer locally and may cascade to regional scales. Notably, walrus feeding activities involve massive bioturbation, which changes benthic community structure, alters sediment, and releases nutrients into the water column. Other large apex predators of Beringia, include four other ice-dependent pinnipeds, sea birds and cetaceans, that play significant ecological roles in energy acquisition, storage, and transfer. Networks of interactions that connect organisms to their environments are central to the capacity of complex, adaptive, heterogeneous ecosystems to attain a high state of order, i.e., minimal entropy, and to resilience—the capacity of a system to recover from disturbance. The further diminishment of sea ice towards disappearance from Beringia is foreseeable, but it is far from clear what state awaits populations of sea-ice-dependent consumer species of Beringia, or to what extent ecosystem resilience may be compromised due to displaced, replaced, or diminished apex predators. At the very least, the overwhelming attention presently given to bottom-up production processes must be amplified by greatly increased emphasis on top-down ecological roles played by apex predators in order better to understand climate-initiated ecosystem change.