Spatial and vertical distribution of phytoplankton pigments in the eastern Atlantic sector of the Southern Ocean Angela Wulff & Sten-Åke Wängberg Marine Botany, Göteborg University, Sweden

WIE SIE APF

SWEDARP 97/98 December 31, 1997, to January 26, 1998 Seawater from 12 stations along a transect at 6°E from to 49.82°S Water depths of 2, 10, 20, 30, 50, 75 and 100 m

Methods 1-2 litres of seawater 20 mm Whatman GF/F glass fibre filters Immediately frozen and stored in liquid nitrogen After 4-8 weeks, the filters were transferred to -85°C 1 ml 100% methanol was added to the filters and the extraction and HPLC-analysis continued according to Wright and Jeffrey (1997)

Detected pigments chl c 3 chl c 1 c 2 chl b chl a peridinin (per) 19’-butanoyloxyfucoxanthin (but) fucoxanthin (fuco) 19’-hexanoyloxyfucoxanthin (hex) diadinoxanthin diatoxanthin alloxanthin (allo) violaxanthin (viol) zeaxanthin (zea) betacarotene

Pigment ratios from Wright et al 1996

APF Dinoflagellates increased along the transect and reached maximum values at 49.8°S Cryptophytes contributed with ca. 3-4% of total biomass Cyanophytes generally constituted 0.5 % of the biomass in the other areas Chlorophytes were identified by the pigments violax and chl b as no other green algal pigments were detected. Chlorophytes constituted ca. 3-5% of total chl a, all depths

WIE Dinoflagellates increased along the transect Cryptophytes contributed with ca. 3- 4% of total biomass Cyanophytes generally constituted 0.5 % of the biomass. However, at 56.7°S, CHEMTAX suggested values of 5-6% between 2-50 m depth and around 1% at 55.8°S, all depths Chlorophytes were very patchily distributed with occasionally high biomass contributions at water depths of m

SIE Dinoflagellates contributed to around 1% of total chl a, increased along the transect Cryptophytes showed a patchy distribution both between depths and areas but were virtually absent in the SIE except for the station at 60.3°S, all depths, and at 30 plus 50 m at 60.4°S Cyanophytes were absent in the SIE and generally constituted 0.5 % of the biomass in the other areas. Chlorophytes were very patchily distributed with occasionally high biomass contributions at water depths of m

In summary 5 different groups were identified: APF < 100 m WIE The northern part of SIE Surface (2-30 m) samples in the southern part of SIE Deep samples (75 & 100 m) in the southern part of SIE Results from Principal Component Analysis (PCA)

Shortcomings of the study Lack of thorough microscopical data. Only very limited microscopical data are available for flagellates except dinoflagellates

The pigment patterns interpreted by CHEMTAX showed that different phyto- plankton assemblages were associated with distinct water masses along the transect. In general, the haptophytes contributed more to total chl a further south and the diatom contribution increased from south to north. In APF, a more diverse phyto- plankton community was found compared with WIE and SIE.

For discussion or most interesting results We found an increasing amount of but and a decreasing amount of hex going from south to north. CHEMTAX suggested up to 80% Hapto-N in the southern part and almost 90% of Hapto-S in the northern part of the transect. Although the microscopical data are sparse, we observed relatively higher amounts of Phaeocystis sp. (colonies) in the southern stations, which contradicts with CHEMTAX results.

Possible explanations The amount of but in haptophytes has been shown to be quite variable. Total fucoxanthins range between 4-20% and 0-24% in colonial and flagellate stages of Phaeocystis antarctica, respectively. Also the absence of but has been reported The pigment composition vary with growth phase. An increased hex/chl a ratio has been shown in stationary growth Influence of light and iron stress. The but concentration in Phaeocystis sp. vary according to light and iron stress, increasing from 0% in low light and low iron to 13% of total fucoxanthins in high light and low iron Other sources than haptophytes could explain the proportion of but. This pigment is also found in pelagophytes and chrysophytes. For example, the pelagophyte Pelagococccus subviridis is widely distributed and it is quite possible that this and related species contribute to the but pool also in Antarctic waters. Recently species of Parmales with the same pigments as in type 4 haptophytes were observed in large amounts in a sample from the Ross Sea

In conclusion CHEMTAX will never completely replace microscopical counts/identifications Basic knowledge of how pigment ratios vary within and between species as well as within and between different microalgal groups are still lacking Despite the points above, we love CHEMTAX