AME 29:107-121 (2002)  -  doi:10.3354/ame029107

Spatial distribution of microbial biomass and activity (bacterivory and bacterial production) in the northern Weddell Sea during the austral summer (January 1994)

Dolors Vaqué*, Juan I. Calderón-Paz, Núria Guixa-Boixereu, Carlos Pedrós-Alió

Institut de Ciències del Mar-CMIMA (CSIC), Departament de Biologia Marina i Oceanografia, Passeig Marítim de la Barceloneta 37-49, 08003-Barcelona, Spain

ABSTRACT: Changes in bacterial production, bacterivory and microbial biomass (autotrophic and heterotrophic) were determined in a complex area characterized by different physico-chemical regimes during the austral summer (January 1994, ECOANTAR-94 cruise). The main goal was to explore the importance of bacterivory as a factor potentially controlling bacterial production in such an extreme environment. The area studied was located in the eastern part of the Bransfield Strait, between 59.5-64°S and 58-50°W. It covered part of the South Shetland Islands shelf and extended northwards to the Weddell-Scotia Confluence and southwards towards the ice edge. Stations were grouped into 4 zones under the influence of different hydrographic conditions: IEZ, influenced directly by the ice edge zone; WS, presenting typical characteristics of the Weddell Sea; FR, located within the Bransfield Strait frontal system and its continuation in the Weddell-Scotia Confluence; and BSO-WSC, containing stations influenced by waters originating in the Bellingshausen Sea and the Weddell-Scotia Confluence. We determined the spatial distribution of microbial biomass (chlorophyll a, bacteria, heterotrophic and phototrophic nanoflagellates and ciliates), bacterial heterotrophic production, and bacterivory. The highest values of chlorophyll a concentration and primary production as well as the lowest grazing rates (0.3 μg C l-1 d-1) and bacterial production values were found at IEZ, together with the lowest temperatures. In contrast, the highest bacterial losses (4.7 μg C l-1 d-1) coincided with high heterotrophic nanoflagellate biomass and bacterial production at the Weddell-Scotia Confluence and waters of Bellingshausen Sea origin (BSO-WSC). These waters showed the highest temperatures, and low chlorophyll a concentration and primary production values. Taking into account the whole data set, bacteria and heterotrophic nanoflagellate biomass explained 68% of the variability in grazing rates. Our results indicated that bacterial losses due to protists represented a large proportion of bacterial production (average 67% d-1). However, the variability detected in the study area was very large (from undetectable to >100%). Therefore, bacterivory does not seem to be the main factor in controlling bacterial production in all the zones studied.

KEY WORDS: Temperature · Hydrographic characteristics · Bacterial abundance · Bacterial production · Protist abundance · Grazing rates · Weddell Sea · Antarctica

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