CONTRIBUTION OF PHOTOSYNTHETIC PICOEUKARYOTES TO PRIMARY PRODUCTION IN BIOGEOCHEMICALLY DISTINCT REGIONS OF THE EASTERN SOUTH PACIFIC OCEAN

Y. M. Rii1, S. Duhamel2, R. R. Bidigare3, M. J. Church1, D. M. Karl1, and D. J. Repeta4

1Department of Oceanography, University of Hawai‘i at Mānoa, Honolulu, HI; 2Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY; 3Hawai‘i Institute of Marine Biology, Kaneohe, HI; 4Woods Hole Oceanographic Institution, Woods Hole, MA

GY TR UP Motivation Result II: Rates of Primary Production

Primary production in the ocean accounts for nearly half of the net global carbon fixation (e.g. Field et al., 1998), and CTD Temperature [°C] Size-fractionated contributions of rates of carbon fixation remained largely invariant across the transect. ----

picophytoplankton (< 3 µm) are dominant contributors to CTD )

-1 Euphotic zone-integrated rates of Contribution of size fractions to Primary production rates were productivity and plankton biomass in oceanic gyres (e.g. d

σ -2 θ primary production primary production determined by measuring the Marañon et al., 2001). However, the contribution of differing [kg m

Depth (m) 1498 14 phytoplankton types to primary production in the ocean is not 1600 100% activities of C-radiolabeled cell -3 incorporation. Despite a ~6-fold ] well-understood. A 80% > 2 μm 1200 difference in rates of primary

production and major 60% BiG RAPA Cruise (18 Nov – 14 Dec 2010) 800 685 differences in phytoplankton Nitrate + Nitrite [ ---- CTD Oxygen [ production • Aim: To examine phytoplankton population structure and rates 40% community composition 0.2-2 μm of primary production in biogeochemically distinct 400 255 between GY and UP, 20% environments in the Eastern South Pacific Ocean. picoplankton were responsible % Contribution to total primary Primary production (mg C m • 0 0% for greater than 60% of total

Sampled 3 regions along natural nutrient and light gradients: Depth (m)

primary production in all regions. μM • UP = St. 1-2, eutrophic, coastal upwelling region μM GY TR UP GY TR UP

] ]

• TR = St. 3-4, oceanic transition zone B • GY = St. 5-7, hyperoligotrophic, open ocean gyre Total Chlorophyll Result III: Picoplankton Contribution to • Sampled 7 stations across a range of surface ocean chlorophyll. Picoplankton contribution to primary production

(Satellite imagery of MODIS chlorophyll from Angel White) ---- % Surface PAR Primary Production Picoeukaryotes Synechococcus Prochlorococcus

100% Contributions of picoeukaryote carbon fixation was

a largely invariant (~40-50%) and nearly equivalent to 80% [mg m GY TR UP Depth (m) picoplanktonic cyanobacteria contribution.

C picoplankton 60%

-3 Cell-specific inorganic carbon fixation rates for picophytoplankton were Arica, ]

determined by measuring the activities of radiolabeled cells sorted on the 1 40% 2 Chile Longitude 3 BD Influx system. Though euphotic zone-integrated cell counts for 4 Prochlorococcus exceeded that of picoeukaryotes by 10- to 100-fold, high Shoaling isopycnal surfaces (A, lines), cold temperature (A, color), and primary production Easter 6 5 20% 7 increased nitrate concentrations (B, color) indicate coastal upwelling in cell-specific rates of productivity for picoeukaryotes resulted in significant Island UP. The deep chlorophyll maximum (DCM) layer (C, color) occurred contributions to picoplankton productivity in all biogeochemical regions. % Contribution to 0%

above the 1% surface photosynthetically active radiation (PAR; C, lines) GY TR UP in UP, at 1% in TR, and below 1% in GY. White dots symbolize depths sampled at each station. Result IV: Picoeukaryote Community Composition

Photosynthetic picoeukaryote communities were spatially distinct.

18S rRNA gene clone libraries were generated by amplifying the DNA of targeted picoeukaryote cells sorted on the BD Influx system. N indicates the # of clones picked per sample type.

Result I: Phytoplankton Abundance and Composition Eukaryotic phytoplankton were dominant contributors to total chlorophyll a (TCHLA) in UP while N = 89 GY SURFACE N = 85 TR SURFACE N = 85 UP SURFACE unicellular cyanobacteria dominated TCHLA in TR and GY. Euphotic zone-integrated* photosynthetic pigments Chrysophytes GY TR UP GY TR UP GY TR UP -2 Nephroselmis-like Ostreococcus spp. TCHLA (mg m ) 17.5 18.5 33.9 Pelagomonas spp. prasinophyte TCHLA > 10 μm 4% 3% 25% Chrysochromulia-

TCHLA 3-10 μm 6% 9% 9% like haptophyte TCHLA 0.2-3 μm 90% 87% 66% Ratio (w:w) DiVinyl CHLA ZEAXanthin DVCHLA:TCHLA Prochlorococcus TR DCM (141 m) Photosynthetic pigment [mg m GY DCM (160 m) Prochlorococcus Cyanobacteria 0.35 0.37 0.20 N = 90 N = 83 N = 156 UP DCM (57 m) ZEAX:TCHLA Cyanobacteria 0.32 0.20 0.18

FUCO:TCHLA Diatoms 0.03 0.02 0.12 Pelagomonas spp. PER:TCHLA Dinoflagellates 0.01 0.01 0.05

HEX:TCHLA Prymnesiophytes 0.25 0.24 0.29 Pycnococcus-like Phaeocystis-like Ostreococcus spp. BUT:TCHLA Pelagophytes 0.12 0.12 0.09 prasinophyte *Trapezoidal integration was performed to the 0.1% surface PAR for St. haptophyte PERidinin 1-6 and to the depth of the DCM for St. 7. Depth [m] FUCOxanthin Diatoms Dinoflagellates Picophytoplankton (< 3 μm) vertical distribution Horizontal scales are not all equal. -3 -1

] Cell abundance (cells ml ) 0.E+00 1.E+05 2.E+05 0.E+00 5.E+04 1.E+05 0.E+00 5.E+03 1.E+04 Summary 0 0 0 • III: Nearly half of the picoplankton contribution to primary • The BiG RAPA transect allowed a cross-system comparison of production was due to picoeukaryotes, whose depth- 19’-HEXanoyloxyfucoxanthin 19’-BUTanoyloxyfucoxanthin 20 20 20 phytoplankton composition and productivity in three Prymnesiophytes Pelagophytes integrated cell abundances were 10- to 100-fold less than biogeochemically distinct environments. 40 40 40 those of Prochlorococcus. Longitude • I: Phytoplankton composition was partitioned between the 60 60 60 • IV: Photosynthetic picoeukaryote community compositions UP regions, with large dinoflagellates and diatoms in UP and Phytoplankton community structure was determined by examining were distinct between depths and regions, indicating that distributions of photosynthetic pigments measured on a Varian 9012 HPLC Depth (m) 80 80 small eukaryotes and unicellular cyanobacteria in all regions. 80 elucidating the diversity of this group of organisms is an and picoplankton cell counts measured on a BD Influx system. Distinct TR • II: > 60% of primary production was contributed by 100 100 100 important endeavor in understanding ecosystem processes. differences were apparent between the phytoplankton assemblages in all 3 picophytoplankton. regions, with large diatoms and dinoflagellates in UP and parts of TR and GY 120 120 120 unicellular cyanobacteria and small eukaryotes in all regions. Prochlorococcus Synechococcus Picoeukaryotes For questions, please contact Yoshimi Rii at [email protected].

References Special thanks to: Tara Clemente, Allison Fong, Elisha Wood-Charlson, Field, C.B., Behrenfeld, M.J., Randerson, J.T., Falkowski, P.G., 1998. Primary Jamie Becker, and Angel White for help during BiG RAPA; Joe Jennings Ocean Sciences Meeting 2014 for nutrient analyses; Ken Doggett, Brandon Carter, and Anne production of the biosphere: integrating terrestrial and oceanic components. Thompson for Influx help; Donn Viviani and Chris Schvarcz for paper Science 281: 237-40. Poster #2843 Session 017 brainstorming and sequence analyses; and the captain and crew of R/V Marañon, E., Holligan, P.M., Barciela, R., González, N., Mouriño, B., Pazó, M.J., Melville. This project was funded by NSF EF-0424599 (DMK). Varela, M., 2001. Patterns of phytoplankton size structure and productivity in contrasting open-ocean environments. Marine Ecology Progress Series 216: 43-56.