The pelagic tunicate Salpa thompsoni is an important member of Southern Ocean mesozooplankton. They especially proliferate in areas with low chlorophyll a concentrations as higher particles concentrations seemingly harm their feeding mechanism. During the European Iron Fertilisation EXperiment (EIFEX, 21.01. 25.03.2004), an eddy in the Southern Polar Frontal Zone was fertilized with Fe(II)SO4 to follow the build-up and fate of an iron induced bloom. Salps from fertilized and unfertilized waters in the eddy showed high gut fluorescence and high experimental fecal pellet production indicating a strong grazing impact in both areas at the beginning of the experiment. Gut fluorescence was significantly higher for in-patch salps which showed no direct signs of clogging. Microscopy and detailed pigment analysis revealed that the phytoplankton composition of adjacent waters down to 500 m was reflected in the salp guts and changed with the developing bloom. Salps generally showed a higher phaeopigment to chlorophyll a ratio than found in the water masses due to digestion. Also, differences in digestion efficiency for different chlorophyll concentrations could be observed. These findings will help to understand the salp distribution especially in the Southern polar sea and their possible impact on the Antarctic food web and downward fluxes.
Helmholtz Research Programs > MARCOPOLI (2004-2008) > POL5-Autecology of planktonic key species and groups