Role of planktonic bacteria in productivity and cycling of organic matter in the Eastern Pacific Ocean

Abstract

Total number, biomass, production, and respiration of bacterioplankton were measured in oligotrophic, mesotrophic and eutrophic waters of the Eastern Pacific. Total number of bacteria in the upper mixed layer and in the upper thermocline boundary layers varied from 30-60.103 ml-' in oligotrophic waters to 100-400. lo3 ml-' in mesotrophic waters of fronts and divergences, and to l-25. lo6 ml-' in eutrophic waters of coastal upwellings. Wet biomass varied from 5-10 mg 1-l in oligotrophic waters, to 50-200 mg 1-l in mesotrophic waters, and to l-2 g m-3 in eutrophic waters. Below the layer of maximum temperature gradient i.e. below 35-50 m, bacterioplankton density decreased 5-10 times. P/B coefficients per day were highest in the oligotrophic surface water (N l), and lowest in the eutrophic ones (0.2-0.4). In mesotrophic waters they were intermediate (0.4-1.0). the stock of labile organic matter (LOM) accessible to microbial action varied from 0.3 to 1.6 mg C l-'. Its highest value occurred in the upwelling area. The stock of LOM does not noticeably decrease from the euphotic zone to a depth of 2000 m. Its turnover time varied from 5 to 45 days in surface waters, and 30-50 years in deep oceanic waters. The role of bacterioplankton in productivity and in cycling of organic matter in surface -and deep oceanic waters is discussed.

Ectoenzymatic activity and bacterial dynamics along a trophic gradient in the Caribbean Sea

“…The potential of oligotrophic bacteria for high growth rates in low-nutrient systems has been shown recently (Yoshinaga et al 1991). High turnover rates of bactenoplankton in oligotrophic situtations were also observed by Sorokin & Mamaeva (1991). The acceleration of this turnover seems to be caused by a change in the primary control mechanism of the bacterioplankton.…”

“…Although bacteria are the dominant biomass component in oligotrophic systems (Dortch & Packard 1989, Fuhrman et al 1989, Cho & Azam 1990, Herndl 1991 the absolute bacterial biomass found in oligotrophic situations is frequently lower compared to those found under eutrophic situations (Billen et al 1990, Sorokin & Mamaeva 1991. As shown in Fig.…”

“…The acceleration of this turnover seems to be caused by a change in the primary control mechanism of the bacterioplankton. Grazing by zooplankton might have a greater impact in controlling bacterial populations in oligotrophic systems (Sorokin & Mamaeva 1991). Billen et al (1990) concluded, based on theoretical assumptions of bactenoplankton dynamics, that the lack of interdependence found between potential bacterial turnover rates and the trophic situation could be explained by a general bottom-up control mechanism for bacterioplankton.…”

“…Studies on the variations of microbial parameters such as standing stocks and production rates along trophic gradients are rare but offer interesting insights into obviously changing food web structures with different trophic stages (Herndl 1991, Sorokin & Mamaeva 1991, Peduzzi & Herndl 1992. Understanding the processes causing these deviations is important to predict the frequently detected inversions of the food web pyramid (Dortch & Packard 1989, Fuhrman et al 1989.…”

“…Under such conditions bacterial biomass accounts for nearly 50 % of the total particulate organic carbon (Cho & Azam 1990). Bacterial production also declines towards oligotrophic systems (Billen et al 1990, Herndl 1991, Sorokin & Mamaeva 1991; it is difficult, however, to compare data given in the literature because of different methodology and conversion factors used (Riemann et al 1987, Cole et al 1988, Torreton et al 1989, Heinanen & Kuparinen 1991. Peduzzi & Herndl(1992) pointed out that bacteria from oligotrophic environments have the ability to grow fast and this growth is stimulated by both the activity of phyto-and zooplankton.…”