D. Dietrich et H. Arndt, Biomass partitioning of benthic microbes in a Baltic inlet: relationships between bacteria, algae, heterotrophic flagellates and ciliates, MARINE BIOL, 136(2), 2000, pp. 309-322
The structure of a benthic microbial food web and its seasonal changes were
studied in the shallow brackish waters of the island of Hiddensee, northea
stern Germany, at two sites in close proximity by monthly or bimonthly samp
ling from July 1995 to June 1996. Abundance and biomass of phototrophic and
non-phototrophic bacteria, heterotrophic flagellates (HF) and ciliates as
well as the biomass of microphytobenthos were determined in the upper 0.3 c
m sediment layer. Abundance of organisms showed strong positive correlation
with water temperature, with the exception of the bacteria. Non-phototroph
ic bacterial numbers ranged from 7 x 10(8) to 6.7 x 10(9) cells cm(-3) and
phototrophic bacterial abundance from 4 x 10(7) to 2.7 x 10(8). Heterotroph
ic protist abundance ranged from 8 x 10(3) to 104 x 10(3) ind cm(-3) for HF
and from 39 to 747 ind cm(-3) for ciliates. The biomass partitioning demon
strated the primary importance of non-phototrophic bacteria (min. 0.83, max
. 84.87 mu g C cm(-3)), followed by the microphytobenthos (min. 1.32, max.
50.93 mu g C cm(-3)). The heterotrophic protists contributed roughly the sa
me fraction to the total microbial biomass, with the biomass of the HF bein
g slightly higher (HF 0.23 to 1.76 mu g C cm(-3), ciliates 0.04 to 1.17 mu
g C cm(-3)). Taxonomic classification of the benthic HF revealed the euglen
ids to be the most important group in terms of abundance and biomass, follo
wed by thaumatomastigids and kinetoplastids. Other important groups were ap
usomonads, cercomonads, pedinellids and cryptomonads, The structure of the
HF assemblage showed strong seasonal changes with euglenids being the most
abundant taxa in summer, while apusomonads and thaumatomastigids were predo
minant in winter. Similar to the pelagic microbial food web, benthic picoph
ototrophic bacteria were occasionally abundant, and the feeding modes of he
terotrophic protists exhibited a great variety (predominantly omnivores, ba
cterivores, herbivores or predators). Filter-feeding HF were of little impo
rtance. Contrary to the pelagic environment, a top-down control on total be
nthic bacterial numbers by HF seemed unlikely at the studied stations which
were characterised by muddy sand.