CARBOHYDRATE COMPOSITION OF PARTICULATE ORGANIC MATTER IN THE NORTHWEST SARGASSO SEA AND IMPLICATIONS FOR MICROBIAL UTILIZATION

The chemical composition of particulate organic matter (POM) in the ocean partially controls its lability/ stability, affecting whether it is exported to the deep ocean and/or consumed or altered by microbial and metazoan food web processing. We used the carbohydrate monomer composition to identify signatures of labile and diagenetically altered POM within the upper 500 m of the water column during three seasons in the northwest Sargasso Sea. Examining size-fractionated POM, we find a high glucose content and high C:N ratios within the upper euphotic zone, especially in large (>20 μm) particles especially during stratified periods when nitrate concentrations were below detection. As depth increased, into the lower euphotic zone and mesopelagic, there was a decrease in glucose contributions and an increase in contributions from monomers deriving from recalcitrant polysaccharides such as peptidoglycan and fucose-based structures. To assess the role of phytoplankton and prokaryotes in shaping the carbohydrate composition of POM, we investigated size-fractionated community composition and abundance and diversity of carbohydrate-active enzymes (CAZymes) within the metagenomes. We observe distinct variations in phytoplankton and heterotrophic prokaryotic communities in both small and large particles over depth. Additionally, the abundance and diversity of CAZymes are distinct between upper euphotic and mesopelagic samples. We will discuss potential linkages between microbial metabolic capabilities and the composition of POM.

Presentation Preference: Oral

Primary Presenter: Lillian Henderson, University of California, Santa Barbara (lillianhenderson05@gmail.com)

Authors:

Lillian Henderson, Department of Ecology, Evolution and Marine Biology, Marine Science Institute, University of California  (lillianhenderson05@gmail.com)

Chance English, Department of Ecology, Evolution and Marine Biology, Marine Science Institute, University of California  (cje@ucsb.edu)

Jacqueline Comstock, Department of Ecology, Evolution and Marine Biology, Marine Science Institute, University of California  (jcomstock@ucsb.edu)

Michelle Michelsen, School of Biosciences, University of Exeter  (michellemichelsen23@gmail.com)

Ben Temperton, School of Biosciences, University of Exeter  (b.temperton@exeter.ac.uk)

Craig Carlson, Department of Ecology, Evolution and Marine Biology, Marine Science Institute, University of California  (craig_carlson@ucsb.edu)

Hilary Close, Department of Ocean Sciences, Rosenstiel School of Marine, Atmospheric, and Earth Science, University of Miami  (hclose@miami.edu)