MICROBIAL COMMUNITY COMPOSITION ON SINKING PARTICLES AS A FUNCTION OF DEPTH AND PARTICLE TYPE IN THE NORTH PACIFIC

Alyson Santoro1, Justine Albers2, Colleen A Durkin3, Matthieu Bressac4, Margaret L Estapa5, Ken Buesseler6, Melissa Omand7, Uta Passow2 and Philip W. Boyd8, (1)University of California Santa Barbara, Santa Barbara, United States, (2)University of California Santa Barbara, Santa Barbara, CA, United States, (3)Moss Landing Marine Laboratories, Moss Landing, CA, United States, (4)University of Tasmania, Institute for Marine and Antarctic Studies, Ecology and Biodiversity, Hobart, TAS, Australia, (5)Skidmore College, Saratoga Springs, NY, United States, (6)Woods Hole Oceanographic Institution, Department of Marine Chemistry & Geochemistry, Woods Hole, MA, United States, (7)University of Rhode Island, Graduate School of Oceanography, Narragansett, RI, United States, (8)Univ Otago, Dunedin, New Zealand
Abstract:
Microbial colonization, respiration, and growth on sinking particles may all influence the depth at which organic matter is remineralized in the ocean. We used 16S rRNA gene sequencing in combination with a novel in situ respiration chamber (RESPIRE) to determine how microbial community composition changes with depth and activity during the EXPORTS North Pacific field campaign. Particles were collected and fixed in situ using traditional particle interceptor sediment traps, neutrally buoyant sediment traps, marine snow catchers, and size-fractionated filtration. We compared these microbial communities to particles incubated in the RESPIRE device to determine the active degraders of sinking organic material. We further compared communities from these bulk particle capture methods to microbes sequenced from individual particles captured in polyacrylamide gel traps. Microbial communities significantly differed based on the method of particle capture. Vibrionales were abundant in bulk trap material at shallow depths (< 200 m), while Oceanospirillales increased with depth. We observed an increase in the relative abundance of fast-growing, copiotrophic taxa such as Alteromonadales on particles after four days of in situ incubation. Nearly identical Alteromonas spp. were identified on individual sinking particles of different types, indicating particles in the size range captured in gel traps are representative of the particles contributing to the measured respiration rates. Particles of different type and origin (aggregates and fecal pellets from diverse zooplankton taxa) harbored remarkably similar microbial communities. The exceptions were salp fecal pellets, which contained a unique community dominated by planctomycete Pirellulales bacteria.