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MEPS 504:91-107 (2014)  -  DOI:

Localised mixing and heterogeneity in the plankton food web in a frontal region of the Sargasso Sea: implications for eel early life history?

Katherine Richardson1,*, Jørgen Bendtsen2, Jens Tang Christensen3, Mohamed Adjou1, Maren Moltke Lyngsgaard1, Karen Marie Hilligsøe3, Jens B. Pedersen3, Torben Vang3, Morten Holtegaard Nielsen4

1Center for Macroecology, Evolution and Climate. Universitetsparken 15, 2100 Copenhagen, Denmark
2ClimateLab, Symbion Science Park, Fruebjergvej 3, Box 98, 2100 Copenhagen, Denmark
3Department of Bioscience, Aarhus University, Ole Worms Allé 1, 8000 Aarhus C, Denmark
4Arctic Technology Centre, Department of Civil Engineering, Technical University of Denmark, Kemitorvet, Building 204,
2800 Kgs. Lyngby, Denmark
*Corresponding author:

ABSTRACT: Previous studies have demonstrated that patches of eel larvae are found in the frontal region of the Subtropical Convergence Zone (STCZ), but to date no clear evidence of why this region might confer advantage to the larvae has been presented. This study demonstrates that there may be localized patches within a frontal region in the STCZ in the Sargasso Sea that experience elevated vertical mixing and an associated vertical flux of nutrients. This localized vertical mixing was suggested by a group of stations within the frontal region that exhibited a greater similarity (Jaccard index) between the diatom communities at 10 m and >100 m (in the deep chlorophyll maximum, DCM) than in other parts of the frontal region. Thorpe displacements supported the hypothesis of elevated mixing intensities around these stations, as did vertical mixing rates inferred from stratification and vertical current shear calculated from acoustic Doppler current profiler (ADCP) measurements. Combining these mixing estimates with vertical nutrient gradients suggests that nutrient fluxes to the euphotic zone at these mixing sites may be an order of magnitude greater than elsewhere in the frontal region. This mixing may influence the plankton food web, as indicated by elevated values/concentrations of (1) primary production, (2) variable fluorescence (Fv/Fm) and (3) total seston. In addition, the fraction of the total biomass of both copepods and nauplii found closest to the DCM in the frontal region correlated with the stratification (Brunt-Väisälä frequency), with the greatest fractions found below 75 m at the most weakly stratified stations. While this study cannot directly link these observations to eel larvae ecology, Munk et al. (2010; Proc R Soc B 277:3593–3599) reported that eel larvae were most abundant at locations where we found evidence for elevated vertical mixing.

KEY WORDS: Plankton · Eel larvae · Sargasso Sea · Mixing · Primary production

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Cite this article as: Richardson K, Bendtsen J, Tang Christensen J, Adjou M and others (2014) Localised mixing and heterogeneity in the plankton food web in a frontal region of the Sargasso Sea: implications for eel early life history?. Mar Ecol Prog Ser 504:91-107.

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