In the biogeochefmical cycles of the ocean, a multitude of processes are catalyzed by Bacteria and Archaea, and the fufnctioning of these cycles in the Barents sea do not differ qualitatively from those at lower latitudes. The carbon cycle may well serve as an example of the biogeochemical cycles (Figure 2.4.1). The heterotrophic procaryotes, denoted bacteria for simplicity, are the major degraders of dissolved organic carbon (DOC), which is their principle source of energy and carbon. At high latitudes, DOC accumulates in the photic zone during the productive season, and the concentration decreases in September/October due to the combination of bacterial degradation and physical mixing processes (Børsheim and Myklestad 1997; Børsheim 2000).
Primary production is the ultimate source of DOC, but all life processes contribute to the transfer from organismal carbon in the primary producers into the pool of DOC (Børsheim et al., 2005). Grazing and predation produces form fecal material which may be released as DOC, or occur as pellets. Fecal pellets may sediment to the seafloor or sometimes getting dissolved in the water column as DOC. The shelf basin of the Barents Sea is fairly shallow and the water column mixes from surface to bottom during winter at many parts of the basin. Therefore resuspension of sediments and leaching of DOC accumulated in sediments provide an additional source of DOC in the Barents Sea, presumably mostly during winter. Figure 2.4.2 shows concentrations of DOC in the Northwestern Barents Sea July-August 1996. High values in the upper 100 meters are DOC accumulated during the productive season, and the high values in the deeper part are presumably a result of sediment resuspension and leaching.
For qualitative specification and overall biomonitoring of aquatic environments estimation of functional activity and reconfiguration of bacterial complex is a critical aspect.
Bacterioplankton from eutrophic areas of the world’s oceans including waters of the Barents Sea is characterized by a wide range of abundances, as well as high variability in structure and functional rates (Teplinskaya, 2001). The total bacterial abundance in the south-eastern sea varies from 1. 4•105 to over 106 cells per ml. The highest total bacterial abundance is in the coastal areas and zones having water masses with different characteristics. Vertical distribution of bacterioplankton is tesselated, with increased abundace in the thermocline layer at the depth of 30 m or lower, in 30-50 m layer. Values of the total abundance and bacterial biomass can vary during the year twice in the mean, with maximal rates observed in spring-summer, and minimal – winter and autumn (Baytaz and Baytaz, 1987; 1991; Teplinskaya, 1990; Mishustina et al., 1997).
Parasitism by viruses also constitutes a source of DOC. This is illustrated by the reproductive cycle of the lytic bacteriophages, which are viruses parasitizing bacteria (Figure 2.4.3). After infecting a bacterial cell and multiplying within the cell at the cost of the bacterial metabolism, the host cell is destroyed in order to let the viral particles to be released to the water. As the cell breaks up dissolved constituents are also released. Not only bacteria, but all other organisms from phytoplankton to mammals are susceptible to virus attacks Brussard et al., 2007; Frada et al., 2008; Marcussen and Have, 1992). Although the bacteriophages have the most extreme effect in that they can completely destroy their hosts, the effect of killing hosts with subsequent release of organic substrate for bacteria is a general consequence of viral infectivity.
For the viruses, the probability of finding a host to infect is dependent on the concentration of hosts. Therefore more dense populations are more likely to suffer from epidemic viral infections than rare populations. The concentration effect on microbial population dynamics has been coined the “killing the winner” hypothesis (Thingstad and Lignell, 1997). The populations that are successful in terms of nutrient acquisition and fast growth will increase their abundance consequently also the probability of propagating their viral parasites. The logical prediction of the hypothesis is that viruses are important in keeping diversity high.
Virus existence seems to incorporate the ability to snatch genes from their hosts, and from other viruses, and transfer them along for benefit of their own existence (Mann et al., 2005).
In addition, sometimes genes from viruses happen to be incorporated in the genomes of their hosts, and it is currently believed that such horizontal transfer of viruses between not related organisms are mediated by viruses and that this is an important factor in evolution (Biers et al., 2008; Lang and Beatty, 2007). Some genes that are transported by viruses are factors of pathogenic ability and have been extensively studied. The gene for toxin production in the bacterium causing cholera is carried by a virus, changing harmless cells of the common estuarine bacterium Vibrio cholera into an extremely potent pathogen of humans (Waldor and Mekalanos, 1996).
The numbers of viruses are in every way staggering. Counted in the microscope, the virus numbers normally exceed bacterial number roughly by a factor of ten. Measured as genotypes, which is a fair proxy for species, there are more than 5000 different types in 100 litres of seawater. In a kg of sediment the number may be around a million (Breitbart et al., 2002; 2004). What is even more intriguing than the diversity of viruses is the diversity within their individual genomes. Clearly every genotype consists of a mosaic of gene sequences with a variety of ages and origins (Dinsdale, 2008).
Both bacteria and viruses show highly variable abundance in the Barents Sea (Figure 2.4.4). A transect in midsummer showed that the concentration of viruses varied from 5•108 to 9•109 particles per litre, and bacterial total counts varied from 5•108 to 6•109 cells•l-1 (Howard-Jones et al, 2002). The viral abundance covaried to a fair degree with bacterial abundance, except for the station farthest north which was ice-covered. Thus in general the dynamics of bacteria and viruses in this area do not differ from other parts of the ocean, but the situation in the ice-covered areas in the north remains to be investigated.
Data on current situation on bacteria and viruses in the Barents Sea is scarce, and is therefore not addressed in Chapter Current and expected state of the ecosystem.