Fig. 1: Hypothesized mechanisms of climate change and fisheries impacts on marine macrofauna biomass and carbon export.

Green (red) arrows represent an increase (decrease) in the pointed process or biological component. The scales on the right represent trade-offs between positive (green weights) and negative effects (red weights) of climate change and fisheries on carbon export. a Schematic representation of the mechanisms leading to a smaller decline in carbon export compared to the decline in biomass. Pathway 1 only considers the impact of biomass reduction on carbon export. Pathway 2 accounts for metabolism acceleration under warmer temperatures, inducing an increase in consumption and fecal pellet production. Pathway 3 combines the reduction of organisms’ body size under a warmer environment and the hypoallometric relationship between body size and consumption, i.e., at equal biomass, small individuals consume more food compared to large ones. Pathways 2 and 3 can partly counterbalance the direct effects of biomass reduction (Pathway 1). b Schematic representation of the mechanisms leading to a smaller decline in fecal pellet production compared to the decline in carcass production. The combination of Pathway 1 (fishing larger individuals leads to a decrease in the size of individuals and a decrease in the non-predation mortality rate, which is size dependent, see Eqs. 18) and 2 (reduced biomass due to selective fishing) leads to a decline in carcass production close to the decline in biomass because no compensatory mechanisms are at play. In parallel, the reduction in biomass (Pathway 2) is slightly offset by the hypoallometric relationship between body size, consumption, and fecal pellet production (Pathway 3). Consequently, the decrease in fecal pellet production is lower compared to that of carcass production. Created in BioRender. Mariani, G. (2025) https://BioRender.com/gujy4c3. Icons made by Good Ware, Muhammad Atif, Freepik, and heisenberg_jr from www.flaticon.com. Icon created in BioRender. Mariani, G. (2025) https://BioRender.com/8hxgiqu.