Rylkova O. Structural and functional indices of bacterioplankton in coastal waters off the Crimea

Present state, seasonal dynamics, and the major structural (abundance: 0,2 - 10,5 106 cells·ml-1; biomass: 2 - 201 mg C m-3; ratio of the cells morphotypes etc.) and functional (specific growth rate: 0,04 - 2,74 day-1, respiration: 0,01 - 1,59 10-9 mg O2 cells-1 day-1) indices of bacterioplankton community in Sevastopol bay and coastal waters off the Southern Crimean are considered for the time period from 1992 to 2007. Intercorrelations between the indices and their dependence on biotic and abiotic factors were examined. Along the gradients of water pollution, the bacterioplankton abundance increased but their functional activity decreased from the open waters to the central part of the Sevastopol bay. Bacterioplankton constituted 45 to 65% of the total biomass of heterotrophic microplankton. Mortality of the bacteria due to their grazing by bacteriovorous plankton was the key factor controlling the community abundance. The interrelation between the bacterial gross growth efficiency and production rate indicated an uncoupling between the energy-producing processes (oxidation of organic matter) and biomass production. This can serve a marker of water pollution. Analysis of the earlier published data and those obtained in this study has revealed long-term trends in bacterioplankton dynamics in Sevastopol bay: a gradual increase from 1966 to 1988, a high variability between 1992 and 2003, and a stable decrease from 2004 to 2007 to the values observed in late 1970s - early 1980s. The latter indicates high ecological capacity of the bay and its capability for a stabilization and recovery if anthropogenic pressure is reduced.