February 1st to 5th 2016
Olhão, Portugal
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Photoprotective response and recovery of phytoplankton communities in the Southern Ocean against high light exposure

Scientific Exhibition
Future Oceans
Wednesday, February 3, 2016 -
18:30 to 20:00

Katayama, T. 1 Makabe, R. 2 Sampei, M. 3 Narita, A. 4 Iida, T. 5 Hattori, H. 6 Sasaki, H. 7 Taguchi, S. 8

1Soka University, Japan
2National Institute of Polar Research
3Hiroshima University
4Ishinomaki Senshu University
5Hokkaido University
6Tokai University
7Ishinomaki Senshu University
8Soka University

Future shoaling of surface mixed layer depth due to an increase in sea surface temperature will expose phytoplankton to increased mean light intensities. One of the photoprotection mechanisms to reduce a damage of photosystem II (PSII) by high light exposure is the heat dissipation of excess energy by xanthophyll pigments. The photoprotective acclimation could determine the ecological success of a species or group in high light conditions. This study investigated the photoprotective response to natural sunlight and recovery in phytoplankton communities during the austral summer in the Australian sector of Southern Ocean.Water sampling were carried out at three stations north (45°S) and south (61°S and 65°S) of the Polar Front (PF) along 110°E in 2014. The phytoplankton communities, collected from subsurface chlorophyll maximum layer, were exposed to sunlight for 2 hours, and were incubated further in the continuous darkness, and 14% and 57% irradiance of sunlight for 3 days.Phytoplankton communities north and south of the PF were dominated by cocolithophores and diatoms, respectively. During the phytoplankton communities were exposed to sunlight, maximum quantum efficiency (Fv/Fm) of PSII decreased around 50% in the all experiments at three stations. The largest increase in diatoxanthin (DT) was observed in the experiment north of the PF under the strongest irradiance during the light exposure experiments. It is suggested that they could reduce the PSII damage by the enhancement of DT synthesis with increasing in the irradiance. When the light-exposed cells were stored in the three light conditions within 3 days, Fv/Fm recovered to more than initial values in the experiment north of the PF, but did not reached to initial values south of the PF. It is suggested that the fast recovery of phytoplankton communities north of the PF may have advantage of acclimating to fast-changing light conditions when the surface mixed layer will be shallower in the Southern Ocean.
keywords: 
Maximum quantum efficiency, Photodamage, Polar Front, Xanthophyll pigments

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