Jfc. De Brouwer et Lj. Stal, Short-term dynamics in microphytobenthos distribution and associated extracellular carbohydrates in surface sediments of an intertidal mudflat, MAR ECOL-PR, 218, 2001, pp. 33-44
Two field studies were conducted to study the in situ net production of ext
racellular carbohydrates and the distribution of benthic diatoms over a per
iod of 24 h per study. A comparison was made between a situation where a cl
ear surface biofilm of diatoms had developed and a situation where this was
not the case, Vertical profiles were made by sampling the top 2 mm of the
sediment at depth intervals of 0.2 mm using the 'cryolander' technique. In
the presence of a biofilm, diatom distribution showed a consistent pattern
when the sediment was emersed. In the light, most of the diatoms were prese
nt in the top 0.2 mm while in the dark, diatoms were homogeneously distribu
ted in the upper 2 mm of the sediment. When a biofilm was absent, no clear
patterns were observed. Extracellular carbohydrates were extracted from the
sediment and separated in 2 operationally defined fractions (colloidal and
EDTA-extractable). The 2 carbohydrate fractions showed a different dynamic
behaviour. The colloidal carbohydrate fraction was highly variable while t
he EDTA-extractable fraction behaved more conservatively. Only in the light
and in the presence of a diatom biofilm, was production of extracellular c
arbohydrates observed, The maximum rate of chlorophyll-normalized productio
n of extracellular carbohydrates, expressed in glucose equivalents (g g(-1)
), amounted to 20 h(-1) in the upper 0.2 mm. The molecular size distributio
n of both carbohydrate fractions was similar. The monosaccharide compositio
n was also similar, except that the EDTA-extractable fraction contained a h
igher percentage of uronic acids, Carbohydrates produced during tidal emers
ion were rich in glucose and were rapidly turned over.