'There is high agreement in model projections that global zooplankton biomass will very likely reduce in the 21st century, with projected decline under RCP8.5 almost doubled that of RCP2.6 . However, the strong dependence of the projected declines on phytoplankton production  and simplification in representation of the zooplankton communities and food web render their projections having low confidence.' The global biomass of marine animals, including those that contribute to fisheries, is projected to decrease by 4.3 + 2.0%  and 15.0 + 5.9% under RCP2.6 and RCP8.5, respectively, by 2080-2099 relative to 1986-2005, while the decrease is around 4.9% by 2031-2050 across all RCP2.6 and RCP8.5 . Regionally, total animal biomass decreases largely in tropical and mid-latitude oceans . 'Projected decrease in upper-ocean export of organic carbon to the deep seafloor is expected to result in a loss of animal biomass on the deep seafloor by 5.2-17.6% by 2090-2100 compared to the present  under RCP8.5 with regional variations . Some increases are projected in the polar regions, due to enhanced stratification in the surface ocean, reduced primary production and shifts towards small phytoplankton . The projected impacts on biomass in the abyssal seafloor are larger under RCP8.5 than RCP4.5 .'
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report