Major community shifts, both gradual and abrupt, are observed in polar oceans in response to warming trends and MHWs   . In general, abundances and ranges of Arctic fish species are declining and contracting, while ranges of boreal fish species are expanding, both geographically and in terms of feeding interactions and ecological roles  , with variable outcomes for large commercial fish stocks . The extreme seasonal solar radiation cycles of these high latitudes may both act as a barrier for species immigration and change predator-prey dynamics in previously ice-covered areas, factors not currently considered in projections  . Responses by marine mammals and birds to the ongoing changes in polar ecosystems are both positive and negative . Phenological, behavioural, physiological and distributional changes are observed in marine mammals and birds in response to altered ecological interactions and habitat degradation, especially to loss of sea ice  . Reproductive failures and declining abundances attributed to warmer polar oceans and less sea ice cover are observed in populations of polar bears, Ursus maritimus, seals, whales and marine birds  . The ongoing changes in polar marine ecosystems can lead to temporary increases in biodiversity and functional diversity , but reduced trophic-transfer efficiencies and functional redundancy, with uncertain consequences for ecosystem resilience and vulnerability  .
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report