Implications of earlier sea ice melt for phenological cascades in arctic marine food webs

Phenological cascades can occur in food webs when the timing of biological activity at one trophic level responds to timing at an adjacent trophic level. Such cascades may therefore be precipitated by changes in abiotic factors that constrain phenology. Arctic marine food webs comprise a series of coupled trophic interactions from primary producers to tertiary consumers under strong temporal control by the annual timing of sea ice melt onset, thinning, and retreat. Under recent climatic warming, the extent, thickness, and age of arctic sea ice have all declined markedly. Simultaneously, the annual timing of sea ice melt has advanced across the Arctic at a rate of − 2 days per decade, with individual regions experiencing advances in melt onset of nearly 25 to 30 days since 1979. This review highlights phenological sensitivity across trophic levels to earlier onset of the annual productive season in arctic marine food webs related to advancing timing of sea ice melt. Phenological dynamics are evident from organisms with the simplest life cycles in these food webs, algae and phytoplankton, to those with the most complex life cycles, bowhead and beluga whales. Phenological responses of arctic marine organisms to the timing of sea ice melt may, however, be stronger at lower trophic levels than at higher trophic levels. Under continued warming, maintenance of the integrity of arctic marine food webs will be sensitive not only to the increasing loss of sea ice cover during summer, but also to increasingly earlier timing of annual sea ice melt onset.