Assessing the time of emergence of global ocean fish biomass using
ensemble climate to fish simulations
Abstract
Climate change is anticipated to considerably reduce global marine fish
biomass, driving marine ecosystems into unprecedented states with no
historical analogues. The Time of Emergence (ToE) marks the pivotal
moment when climate conditions (i.e. signal) deviate from pre-industrial
norms (i.e. noise). Leveraging ensemble climate-to-fish simulations,
this study examines the ToE of epipelagic, migratory and mesopelagic
fish biomass, alongside their main environmental drivers, for two
contrasted climate-change scenarios. Globally-averaged biomass signals
emerge over the historical period. Epipelagic biomass decline emerges
earlier (1950) than mesozooplankton decline (2000) due to a stronger
signal in the early 20th century, possibly related to trophic
amplification induced by an early-emerging surface warming (1915).
Trophic amplification is delayed for mesopelagic biomass due to
postponed warming in the mesopelagic zone, resulting in a later
emergence (2000). ToE displays strong size class dependence, with medium
sizes (20 cm) experiencing delays compared to the largest (1 m) and
smallest (1 cm) categories. Regional signal emergence lags behind the
global average, with median ToE estimates of 2029, 2034 and 2033 for
epipelagic, mesopelagic and migrant communities, respectively, due to
systematically larger local noise compared to global one. These ToEs are
also spatially heterogeneous, driven predominantly by the signal
pattern, akin to mesozooplankton. Additionally, our findings underscore
that mitigation efforts (i.e. transitioning from SSP5-8.5 to SSP1-2.6
scenario) have a potential to curtail emerging ocean surface signals by
40%.