J.H. Paul
L. Campbell
D. Griffin
L. Houchin
A. Fuentes-Ortega
F. Muller-Karger
B. Wawrik
2003
<p><span>Low salinity plumes of </span>coastal<span> origin are occasionally found far offshore, where they display </span>a<span> distinct color signature detectable by satellites. The impact of such plumes on carbon fixation and </span>phytoplankton<span> </span>community<span> </span>structure<span> </span>in<span> </span>vertical<span> profiles and on basin wide scales is poorly understood. On </span>a<span> research cruise </span>in<span> June 1999, ocean-color satellite-images (Sea-viewing Wide Field-of-view Sensor, SeaWiFS) were used </span>in<span> locating </span>a<span> Mississippi River </span>plume<span> </span>in<span> the eastern </span>Gulf<span> of </span>Mexico<span>. Profiles sampled within and outside of the </span>plume<span> were analyzed using flow cytometry, HPLC pigment analysis and primary production using </span><sup>14</sup><span>C incorporation. Additionally, RubisCO large subunit (rbcL) gene expression was measured by hybridization of extracted RNA using 3 full-length RNA gene probes specific for individual </span>phytoplankton<span> clades. We also used </span>a<span> combination of RT-PCR/PCR and TA cloning </span>in<span> order to generate cDNA and DNA rbcL clone libraries from samples taken </span>in<span> the </span>plume<span>. Primary productivity was greatest </span>in<span> the low salinity surface layer of the </span>plume<span>. The </span>plume<span> was also </span>associated<span> with high Synechococcus counts and </span>a<span> strong peak </span>in<span> Form IA rbcL expression. Form IB rbcL (green algal) mRNA was abundant at the subsurface chlorophyll maximum (SCM), whereas Form ID rbcL (chromophytic) expression showed little </span>vertical<span> </span>structure<span>. Phylogenetic analysis of cDNA libraries demonstrated the presence of Form IA rbcL Synechococcus phylotypes </span>in<span> the </span>plume<span>. Below the </span>plume<span>, 2 spatially separated and genetically distinct rbcL clades of Prochlorococcus were observed. This indicated the presence of the high- and low-light adapted clades of Prochlorococcus. </span>A<span> large and very diverse clade of Prymnesiophytes was distributed throughout the water column, whereas </span>a<span> clade of closely related prasinophytes may have dominated at the SCM. These data indicate that the Mississippi river </span>plume<span> may dramatically alter the surface picoplankton composition of the </span>Gulf<span> of </span>Mexico<span>, with Synechococcus displacing Prochlorococcus </span>in<span> the surface waters.</span></p>
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10.3354/meps251087
en
Inter-Research Science Publisher
Vertical structure of the phytoplankton community associated with a coastal plume in the Gulf of Mexico
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