A trait-based carbon export model for mesopelagic fishes in the Gulf of Mexico with consideration of asynchronous vertical migration, flux boundaries, and feeding guilds

Abstract

Fish-mediated carbon export provides a significant proportion of the biological carbon pump in oligotrophic regions. Bioenergetic models estimate this carbon transport, but many lack species-specific traits and no carbon export model has been developed in the mesopelagic Gulf of Mexico. Intensive mesopelagic sampling efforts in the northern and eastern Gulf of Mexico have provided high-resolution information regarding community composition, species' vertical migratory characteristics, diel depth occupancies, and diets. A stochastic, individual-based model was developed for deep-pelagic fishes in the northern Gulf of Mexico to estimate bioenergetic rates and carbon export fluxes. Fishes that ate gelatinous zooplankton consumed more mass per body weight per day than predators of cephalopods and fishes, ostensibly to increase the throughput of prey with less carbon (gelata) or more refractory materials (Crustacea). A dynamic energy budget submodel indicated that during 81% of occurrences, asynchronous vertically migrating fishes rested for 1 d before migrating again, but migrations on successive days were possible. In terms of carbon export, myctophids and stomiids contributed greater than 53% and 12% of the active carbon flux for the entire assemblage in all scenarios. The assemblage-wide carbon export rate driven by vertically migrating fishes was 0.14–0.72 mg C m⁻² d⁻¹, 61% of the ingested carbon by the assemblage. Incorporating species-specific traits and individual variability in bioenergetic models allows for more complex research questions (e.g., the effect of feeding guilds and asynchronous migration on carbon export) compared to the carbon export models that otherwise assume all fishes within a functional group are equivalent.