UC San Diego

Mesopelagic fishes are of utmost importance to the health of global oceanic ecosystems. These fishes comprise the largest known marine biomass, and are a vital source of food many economically important fish and marine mammals. Further, they serve as a major component of the biological carbon pump, moving food items through the water column via diel migration. Though significant effort has gone into understanding species diversity, and positioning in marine food webs, the microbial component of these animals remains poorly characterized. Symbiotic microbial populations associated with the gastrointestinal (GI) tract assist the host with nutrient uptake, digestion, defense against pathogenic microbes, but can also be detrimental to host health as parasites or pathogens. This study investigates the normal intestinal microbiota of wild mesopelagic fish to determine community diversity and distribution across multiple host families with varying migratory and dietary lifestyles. The results presented here indicate that midwater fish have unique microbial communities from fish of other pelagic zones, where, for example, mesopelagic hosts show enrichment in Betaproteobacteria and Gammaproteobacteria microbial classes. Within mesopelagic fish families, major differences were seen: Gonostomatidae are enriched in three Mycoplasma taxa, Stomiidae had highest alpha diversity, Melamphaidae had the highest abundance of Planctomycetes, and Myctophidae gut communities were enriched in Betaproteobacteria. This study brings new understanding to the microbial ecology of the mesopelagic, and demonstrates that despite sharing space in the water column, mesopelagic fishes contain different microbial communities. Clearly, life history traits must be considered in addition to environment in order to better understand the mesopelagic ecosystem.

Mesopelagic fishes are of utmost importance to the health of global oceanic ecosystems. These fishes comprise the largest known marine biomass, and are a vital source of food many economically important fish and marine mammals. Further, they serve as a major component of the biological carbon pump, moving food items through the water column via diel migration. Though significant effort has gone into understanding species diversity, and positioning in marine food webs, the microbial component of these animals remains poorly characterized. Symbiotic microbial populations associated with the gastrointestinal (GI) tract assist the host with nutrient uptake, digestion, defense against pathogenic microbes, but can also be detrimental to host health as parasites or pathogens. This study investigates the normal intestinal microbiota of wild mesopelagic fish to determine community diversity and distribution across multiple host families with varying migratory and dietary lifestyles. The results presented here indicate that midwater fish have unique microbial communities from fish of other pelagic zones, where, for example, mesopelagic hosts show enrichment in Betaproteobacteria and Gammaproteobacteria microbial classes. Within mesopelagic fish families, major differences were seen: Gonostomatidae are enriched in three Mycoplasma taxa, Stomiidae had highest alpha diversity, Melamphaidae had the highest abundance of Planctomycetes, and Myctophidae gut communities were enriched in Betaproteobacteria. This study brings new understanding to the microbial ecology of the mesopelagic, and demonstrates that despite sharing space in the water column, mesopelagic fishes contain different microbial communities. Clearly, life history traits must be considered in addition to environment in order to better understand the mesopelagic ecosystem.