declines  are -5.7 + 4.1% and -15.5 + 8.5% under SSP1-2.6 and SSP5-8.5, respectively, by 2080-2099 relative to 1995-2014 , showing greater declines and lower inter- model uncertainties . These declines result from combined warming and decreased primary production  and are amplified at each trophic level within all ESM and marine ecosystem model projections across all scenarios  . However, there is limited evidence about how underlying food-web mechanisms amplify the climate signal from primary producers to higher trophic levels, and several putative mechanisms have been proposed . As assessed in SROCC, the biomass projections contain considerable regional variation with declines in tropical to temperate regions and strong increases in total animal biomass are projected in polar regions under high-emission scenarios, with climate-change effects
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report