Ocean optics meets taxonomy: case study in Southern Adriatic Pit1 2 3 1 1 1 4 5 5 1Bošnjak I. , Petrić I , Cetinić I. , Bosak S. , Mejdandžić M. , Kružić P. , Mihanović H. , Miloslavić M. , Lučić D. , Ljubešić Z.

1Department of Biology, Faculty of Science, University of Zagreb, Zagreb, Croatia; 2Division for Marine and Environmental Research, Ruđer Bošković Institute, Zagreb, Croatia;

3 NASA Goddard Space Flight Center/USRA, Ocean Ecology Laboratory, Greenbelt, MD, United States; 4Physical Oceanography Laboratory, Institute of Oceanography and Fisheries, Split, Croatia;

5Institute for Marine and Coastal Research, University of Dubrovnik, Dubrovnik, Croatia

The immense diversity of oceanic plankton and its distribution is hard to access with a single method only. Discrete samples, analysed through imaging, pigments or molecular methods, offer a great view of the composition, but offer only a limited resolution of plankton over space and time. Optical tools, deployed on in situ and from remote sensing platforms, allow high spatial and temporal view, but tell very little about plankton composition. However, combination of these techniques offers an all-inclusive view of plankton diversity in the ocean.

WHERE?BIOTA [Bio-tracing Adriatic water masses] Winter Cruise was conducted in oligotrophic waters of the Southern Adriatic Pit (Figure 1.)

WHYAim: specific winter circulation &

distribution of phytoplankton

Two major transects: 1. Dubrovnik to 1000 m isobath (in direction 210º)2. 1000 m isobath to Lastovo

Influence of: - Levantine Intermediate Water (LIW) - East Adriatic Current (EAC)

HOWPhysicsCTD casts - temperature, salinity, oxygen, light (PAR) Optical analysis (biology): CTD casts - chlorophyll fluorescence, particulate backscattering and beam attenuation derived data- particulate organic and phytoplankton carbon, optical indices (optical community index and backscattering ratio)Phytoplankton and zooplankton abundances: microscopy, flow cytometry and molecular identification methods

CONCLUSIONEncountered distribution of the plankton in the water column reflects an intricate play of the water masses in the studied area. Overall, our results suggest that different portions of plankton community, here separated by their size, respond to different environmental cues in this oligotrophic oceanic ecosystem.

1.2.

J. Godrijan

ACKNOWLEDGMENTSThis work was fully supported by Croatian Science Foundation under the project 6433.

A New Age of Discovery for Aquatic MicroeukaryotesEMBL Heidelberg, Germany

26 January - 29 January 2016

Figure 1. Map of investigated area with satelite photographs taken February 18 2015., a week before the BIOTA cruise showing Chl a concentrations and two investigated transects with stations as red dots.

OVERVIEW

WHENth rdFebruary 28 - March 3 2015

Combination of techniques!

1% PAR

Station P100 (28/2/2015)(»control station» for optical parameters - no surprises there)

Physics Biology Biology

Figure 2. Vertical profiles at P100 station of a - temperature, salinity and oxygen concentration; b - Chl a values from CTD cast and derived particulate organic carbon and phytoplankton carbon; c - optical community index and backscattering ratio; d - phytoplankton groups

Optics

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Dominance of DIATOMS

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Average zooplankton densities showed graduate decrease with dep th . Unexpec ted ly, h igh numbers of microzooplankton were recorded at all stations, with average densities greater than 10

-3000 ind. m in the upper 300 m of the water column., while lowest abundances were recorded at P600 station.

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P600 (1/3/2015)Picophytoplankton (picoeukaryotes) and zooplankton

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Figure 10. Light micrographs of Picochlorum sp. clone isolated at station P600. Vegetative cells and cells in autosporulation. White arrows indicate cell division and mother cell wall; black arrows indicate large lobbed chloroplast.

Figure 9. Vertical profile of picophytoplankton groups. yellow arrow: layer with min oxygen & chl values, green arrow: picoeukaryote abundance maximum.

Figure 8. Vertical profiles at P600 station of a - temperature, salinity and oxygen concentration; b - Chl a values from CTD cast and derived particulate organic carbon and phytoplankton carbon; c - optical community index and backscattering ratio; yellow arrow: layer with minimal oxygen & Chl a values, green arrow: picoeukaryote abundance maximum

Optics

Figure 11. Microzooplankton abundance at P600 station -3(no. ind.m )

5µm 10µm

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Figure 4. Some of the coccolithophore species recorded at P150A station. a - Emiliania huxleyi; b - Umbilicosphaera sibogae; c - Helicosphaera HOL dalmaticus type d - Calcidiscus leptoporus. Photographs by J. Godrijan.

1% PAR

P150A (3/3/2015)picophytoplankton (cyanobacteria) and coccolithophores

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Figure 3. Vertical profiles at P150A station of a - temperature, salinity and oxygen concentration; b - Chl a values from CTD cast and derived particulate organic carbon and phytoplankton carbon; c - optical community index and backscattering ratio; d - phytoplankton groups

Optics

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Dominance of COCCOLITHOPHORES

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Figure 5. Vertical profile of nanophytoplankton groups. Figure 6. Vertical profile of picophytoplankton groups.

Figure 7. ITS-based neighbour-joining phylogenetic trees showing the inferred evo lu t i ona ry re la t i onsh ips among Prochlorococcus sequences retrieved from the Adriatic sea (station P150A) collected at depths 20 m (a), 80 m (b) and 140 m (c) in r e l a t i on t o p rev i ous l y sequenced Prochlorococcus. Phylogenetic clade affiliation is indicated at right: HL—High light adapted, LL—Low light adapted, as determined by physiological studies of isolates.