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The article presents a study on the carbon transfer between herbivore and microbial loop-dominated food webs and its implication to fish production. It states that the study was performed in the southern Barents Sea during spring and summer. Herbivorous food web dominated the system during spring in which the diet of protozoa consists of bacteria and phytoplankton. When the microbial loop dominated the food chain in the summer, four times more bacteria were ingested by protozoa than phytoplankton. Young cod Gadus morhua aged less than 3 year old depends on microbial loop while adults relied less on microbial loop and preyed more herbivorous krill. It concludes that fish production was comparable between spring and summer seasons.

Seasonal and geographical variations of suspended single-celled organisms on a transect across the western part of the Barents Sea in March and May 1998 and in June–July 1999 revealed that pico- and nanoplankton flagellates and monads (<2 and 2–20 μm, respectively) entirely dominated total algae and protozoa numbers and biomass in March and in June–July, but in May, microplankton (>20 μm) prevailed in total biomass. In general, spring bloom progresses independently of the southern part of the Atlantic Water (AW) and follows the receding ice edge in the Arctic Water (ArW) to the north. The blooms started almost simultaneously and had similar composition (small diatom Chaetoceros socialis dominated total phytoplankton biomass) in both localities, so the share of resting spores, indicating the age of the bloom, differed markedly. As for underwater rise—the Sentralbanken (SBW) altered this pattern, and the spring bloom spreads from north to the south from the rise to the trench. The next stage of the bloom was dominated by the large diatoms Thalassiosira antarctica var. borealis above the Sentralbanken, in the Polar Front (PF) and in the ice-edge areas. In the southern part of transect, this stage of the spring bloom had a delay or was absent due to low stability of water column and/or due to grazing impact. The presence of ribbon-shaped forming species indicated the earlier stage of bloom in Marginal Ice Zone (MIZ). In May 1998 as well as in June/July 1999, at the ice-covered stations, early spring conditions—rather similar to the conditions in March 1998—were observed. Summer conditions at most of the stations in June–July 1999 were characterized by high species diversity of diatoms and dinoflagellates. High abundance of heterotrophic dinoflagellates and protozoans indicated the active functioning of the microbial loop in the nutritive chains. [Copyright &y& Elsevier]

In a transect across the Barents Sea into the marginal ice zone (MIZ), five 24-h experimental stations were visited, and uptake rates of NH4+ and NO3− by bacteria were measured along with their contribution to total dissolved inorganic nitrogen (DIN) assimilation. The percent bacterial DIN uptake of total DIN uptake increased substantially from 10% in open Atlantic waters to 40% in the MIZ. The percentage of DIN that accounted for total bacterial nitrogen production also increased from south to north across the transect. On average, at each of the five 24-h stations, bacteria accounted for 16–40% of the total NO3− uptake and 12–40% of the total NH4+ uptake. As a function of depth, bacteria accounted for 17%, 23%, and 26% of the total NH4+ assimilation and 17%, 37%, and 36% of the total NO3− assimilation at 5, 30, and 80 m, respectively. Bacteria accounted for a higher percentage of total NO3− uptake compared to total NH4+ uptake in 12 out of 15 samples. Bacterial productivity explains a substantial amount of the variability associated with bacterial DIN uptake, but the relationship between bacterial production and bacterial DIN uptake is best explained when the data from the open Atlantic water stations are grouped separately from the MIZ stations. The percentage of DIN that accounts for bacterial N production is approximately four-fold higher in 24 h MIZ stations compared with open Atlantic stations. This suggests that bacteria play a larger role in NO3− utilization, particularly in the MIZ, than previously hypothesized and that bacterial uptake of NO3− should not be ignored in estimates of new production. Understanding processes that affect autotrophic based new production, such as heterotrophic bacterial utilization of NO3−, in polar oceans is of particular significance because of the role these regions may play in sequestering CO2. [Copyright &y& Elsevier]