Distribution and chromatic adaptation of phytoplankton within a shelf sea thermocline

Hickman, Anna E., Holligan, Patrick M., Moore, C. Mark, Sharples, Jonathan, Krivtsov, Vladimir and Palmer, Matthew R. (2009) Distribution and chromatic adaptation of phytoplankton within a shelf sea thermocline. Limnology and Oceanography, 54 (2), 525-536.

Abstract

Observations of vertical gradients in phytoplankton community structure were made through the water column of
the seasonally stratified Celtic Sea, including within the thermocline. A deep chlorophyll maximum (DCM) was
located within the thermocline at all stations, coupled to the nitracline. Vertical gradients in phytoplankton
community composition were routinely observed within the thermocline. The cell abundance maxima for
Synechococcus occurred in the upper part of the DCM coincident with a picoeukaryote abundance minima.
Picoeukaryote abundance typically increased at or just above the peak of the DCM. Diatoms were observed
occasionally at the DCM peak. Pigment compositions and phytoplankton absorption spectra indicated that the
different phytoplankton communities were chromatically well adapted to the spectral composition of irradiance at the
depths where they occurred in the water column. Profiles of vertical eddy diffusivity revealed that timescales formixing
between the phytoplankton layers within the thermocline were in excess of typical phytoplankton growth rates. The
observed vertical gradients in community structure could therefore result from selection and niche partitioning of
phytoplankton types on the light and nutrient gradient within the thermocline. The data further indicate that the
pigments, light absorption characteristics, and cell size contribute to the phytoplankton selection process.

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Contributors

Author: Anna E. Hickman

Author: C. Mark Moore

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