T. Mock et al., BACTERIA IN SEA-ICE AND UNDERLYING BRACKISH-WATER AT 54-DEGREES-26'50''N (BALTIC SEA, KIEL BIGHT), Marine ecology. Progress series, 158, 1997, pp. 23-40
Bacterial response to the rare event of solid ice cover in the western
Baltic Sea (Kiel Eight) was investigated from February to March 1996.
Samples (ice cores, brine and water) were taken at a shallow, near-sh
ore station at irregular time intervals. Bacterial abundance, biomass
and production were measured in brine and the underlying water as were
the concentrations of NO3, NO2, NH4, PO4 and SiO4. Vertical distribut
ions of bacterial abundance, biomass, morphotypes and size classes and
chlorophyll a and nutrients were investigated within sea ice. A bacte
rial growth experiment with brine bacteria was carried out to measure
bacterial carbon production via total incorporation of [H-3]thymidine
(TTI) and [H-3]leucine (TLI). During February the abundance, biomass a
nd production of bacteria within brine exceeded values from under-ice
water, whereas the opposite was observed in March. High NO3 and NH4 co
ncentrations in ice and under-ice water of up to 112 mu M and 55 mu M,
respectively, resulted in N:P ratios of 18 to 330. Algae and bacteria
were considered to benefit from that nutrient supply. For bacteria th
is was supported by TTI and particularly high TLI rates during the ice
situation, with TLI:TTI ratios of 25 to 213. The high TLI rates were
due to a large degree of unspecific labeling by leucine and characteri
sed the bacteria during winter 1996 as extremely active. Bacterial pro
duction (based on TTI) rose in water from 0.021 mu g C 1(-1) h(-1) at
the beginning to 0.909 mu g C 1(-1) h(-1) at the end of the investigat
ion, and in brine from 0.122 to 0.235 mu g C 1(-1) h(-1). Abundance of
bacteria in brine increased from 1.7 x 10(6) cells ml(-1) initially t
o 2.8 x 10(6) cells ml(-1) in March. The average cell volume of these
bacteria was 0.2 mu m(3) whereas the bacteria in water reached only 0.
08 mu m(3). The bacterial assemblage in the ice was dominated by large
rods and in the water by small rods and cocci. Bacterivorous activity
within sea ice was assumed to be reduced due to the specific vertical
distribution of the different bacterial size classes. This Was furthe
r supported by a good correlation between the development of the bacte
rial standing stock and the potential biomass, in sea ice as well as i
n the underlying water, calculated from generation times towards the e
nd of the investigation. Low grazing pressure, high standing stocks of
algae and sufficient substrate supply accounted for bacterial biomass
within the ice and the underlying water that exceeded that from forme
r winters by far. A comparison with Arctic and Antarctic sites demonst
rated that the bacterial community within the sea ice showed many simi
larities to those found in sea ice of polar regions.