In order to investigate survival of diatoms and long-term pigment dynamics in dark sediment, we incubated
samples of homogenized, sieved, tidal-flat sediment for 1 yr in darkness. Microscopic observations revealed that
some diatoms survived the full year in darkness and retained their pigments. Concentrations of the diatomspecific
phospholipid-derived fatty acid (PLFA) 20:5v3 indicate that these survivors represented only a small
fraction of the original diatom community, probably no more than a few percent. Consequently, the effect of
pigment retention in living diatoms on the overall pigment dynamics was negligible. The photosynthetic potential
of the surviving diatoms was further investigated by re-exposing the sediment to light in the presence of 13Cbicarbonate.
Rapid 13C fixation into algal PLFAs at a level similar to that in sediment freshly collected from the
field indicates that surviving diatoms fully retained their photosynthetic capacity. Concentration dynamics of
photosynthetic pigments generally reflected degradation of two different pools with clearly different loss rates.
Losses during the first 1–2 months of the experiment (half lives of 6–22 d) reflected degradation of fresh algal
material, while losses during the rest of the experiment reflected much slower degradation of more refractory
pigment pools (half lives of $ 1 yr). Individual pigments showed distinctly different labilities, with losses ranging
from 0% to 86% over the full year. The order of overall loss was fucoxanthin . chlorophyll c . chlorophyll a .
diadinoxanthin . pheophorbide . pheophytin . diatoxanthin.