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MEPS 255:55-80 (2003)
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Abstract
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Phytoplankton assemblage structure and primary productivity along 170°W in the South Pacific Ocean
Giacomo R. DiTullio1,*, Mark E. Geesey1, David R. Jones1,2, Kendra L. Daly3, Lisa Campbell4, Walker O. Smith Jr5
1University of Charleston, Grice Marine Laboratory, Charleston, South Carolina 29412, USA
2Rutgers University, Haskins Shellfish Research Laboratory, Port Norris, New Jersey 08349, USA
3College of Marine Science, University of South Florida, St. Petersburg, Florida 33701, USA
4Department of Oceanography, Texas A&M University, College Station, Texas 77843-3146, USA
5Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, Virginia 23602, USA
*Email: ditullioj@cofc.edu
ABSTRACT: Phytoplankton pigments were measured using HPLC during non-ENSO conditions in mid-summer along a South Pacific transect from 67°S to the equator along 170°W. Highest concentrations of chlorophyll a (chl a) occurred in the Polar and
the Subtropical Fronts (PF and STF, respectively) with concentrations exceeding 500 ng l-1. In the STF, there was a distinct subsurface chl a maximum (SCM) at 40 m, which gradually deepened northward to 120 m in the Subtropical
Convergence Zone. Northwards, the SCM shoaled to about 30 m in the Equatorial Zone (EZ). Relatively high concentrations of fucoxanthin and 19'-butanoyloxyfucoxanthin occurred in the nutrient-rich waters south of the Subantarctic Front, and ChemTax
analyses indicated that diatoms, chrysophytes, pelagophytes, and haptophytes dominated the phytoplankton assemblage. Northward of the PF to the STF, where silicate concentrations were <1 µM, pelagophytes and coccolithophorids dominated the water
column; diatoms were virtually absent, and Phaeocystis, prasinophytes, cryptophytes, and chlorophytes contributed significantly to the total algal biomass. Phaeocystis populations were dominant at or below the 1% light level. In the South
Pacific Gyre (SPG), Synechococcus (Syn) and Prochlorococcus (Pro) were major components of the phytoplankton assemblage with Pro dominant as indicated by both flow cytometry and by the ratio of divinyl chl a:total
chl a (0.43 ± 0.07). Photoacclimation by Pro in the SPG was pronounced, with a higher average divinyl chl a per cell ratio in the SCM (1.1) relative to values (0.1) in the upper waters (0 to 100 m). Primary production rates exceeding
1 µg C l-1 h-1 occurred at the surface in the STF. Surface primary production rates were generally <0.4 µg C l-1 h-1 across the SPG, but exceeded 1.4 µg C l-1 h-1 at the equator. In the
EZ, Pro dominated the phytoplankton assemblage, but Phaeocystis and prasinophytes were also major constituents of the assemblage.
KEY WORDS: Phytoplankton assemblage · Photosynthetic pigments · Productivity · Antarctic Circumpolar Current · South Pacific Gyre · Equatorial upwelling · ChemTax
Full text in pdf format
Published in MEPS Vol.
255
(2003) on June 24
Print ISSN: 0171-8630; Online ISSN: 1616-1599.
Copyright © Inter-Research, Oldendorf/Luhe, 2003
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