Abundance and biomass of heterotrophic microbes in the Kongsfjorden, Svalbard

1Introduction Heterotrophicmicrobesarenowconsideredtobe significantcomponentsofthestructureandfunctionof marinepelagicecosystems.Heterotrophicbacteriacon- stituteamajorpoolofbiomassinopenecosystem (WilhelmandSuttle,1999).Theyconsumealargepor- tionofprimaryproduction(Li,1998;Sherryetal., 2002;Lietal.,2004),andtheymineralizemostofthe dissolvedorganiccarbonthattheyconsume(Azamet al.,1983;Richetal.,1997;Azam,1998).Therolesof planktonicprotists,suchasheterotrophicflagellates andciliates,inmicro…

Abundance and biomass of heterotrophic microbes in the Kongsfjorden, Svalbard

Abundance and biomass of heterotrophic microbes were investigated using epifluorescense microscopy in August 2004 along a transect in the Kongsfjorden, a glacial fjord in the high arctic, located in the north-western part of Svalbard. A bacterial abundance was low at outer fjord stations (on average 2.29 × 108 ind./dm3) and was higher at inner fjord stations (on average 3.52 × 108 ind./dm3).The biomass of bacteria ranged from 3.69 to 8.01 mg/m3.The abundance of bacteria was low at the surface of water(0 m), whereas the higher abundances often occurred at depths of 30～50 m. The abundance of heterotrophic flagellates varied from 2.785 to 8.891 × 104 ind./dm3.The assemblage was numerically dominated by less than 5 μm heterotrophic flagellates (78.67%～94.80%).The biomass of heterotrophic flagellates varied from 0.37 to 2.30 mg/m3.The mean biomass distribution for all stations was 4.91% for less than 5 μm heterotrophic flagellates, 86.74% for 6～20 μm flagellates and 8.35% for greater than 20 μm sized flagellates.The lowbiomass of heterotrophic flagellates often occurred at the surface of water (0 m),while the maximum value of biomass occurred at different depths.The biomass of total heterotrophic microbial community ranged from 4.20 to 10.03 mg/m3.The mean biomass distribution for all stations was 82.58% for bacteria, 15.77% for flagellates and 1.66% for ciliates.