Centro de Investigación Oceanográfica en el Pacífico Sur Oriental (COPAS), Departamento de Oceanografía, Universidad de Concepción, Casilla 160-C, Concepción, Chile, Tel: +56 41 204239, Fax: +56 41 256571, E-mail: rquinone@udec.cl
Respiration and biomass by
size in a highly productive upwelling system off Central-south Chile
A study of the size-distribution of biomass and potential respiration in the pelagic ecosystem was carried out off central-south Chile. This upwelling ecosystem has annual primary production levels among the highest ever reported in the literature providing approximately 4% of the worldwide fish captures. Nevertheless, the biogeochemical pathways and the structure/functioning of the trophic web remains poorly understood. Here, we analyze the energy expenditure of the plankton community using body-size as the organizing criterion and we also test whether the regularities observed in the biomass and respiration size-spectra of more stable ecosystems hold under these far from equilibrium conditions.
Two cruises were conducted (36º to 38ºS) from the coast to 200nm offshore, during the spring 1998 and winter 1999. Biomass was determined as ATP and potential respiration was estimated using the electron transport system activity (ETSA). The samples were size-fractionated onboard generating a total of 12 size-classes per spectrum (from 0.7 to 8000 um).
The distribution of biomass and respiration by size in the spring and winter cruises can be described by linear normalized biomass (NBSS) and respiration (NRSS) size-spectra, respectively. The slope of the NBSS ranged from –0.97 to –1. 25 during the spring and from –0.86 to –1.56 during the winter, indicating wide variability in the distribution of biomass by size in both periods. The slopes of the NRSS ranged between –1.19 and –1.64 during October 1998 and between –1.39 and –1.79 during July 1999, although in some cases important residuals are observed.
The ETSA/Biomass ratio through the size-spectrum was almost constant, although its slope (–0.06) indicates a slight higher energy expenditure per unit biomass in the smaller size classes. Our results support the hypothesis that the distribution of respiration by size is a very conservative property of pelagic ecosystems. The biogeochemical significance of the size distribution of energy expenditure in this planktonic community in terms of carbon demand and CO2 production is discussed.