Enhancement of microplankton respiratory activity in the Almería-Oran Front (Western Mediterranean Sea)

Abstract

The activity of the respiratory electron transfer system (ETS) in microplankton (<200 μm cell size) was measured along depth profiles from the surface to 100 m in the Almería-Oran Front (Eastern Alboran Sea). ETS activity gives an estimation of respiratory metabolism of plankton that can be compared with biomass and primary production values. Three regions, Frontal Water (FW), Mediterranean Surface Water (MSW) and Modified Atlantic Water (MAW), were sampled. Chlorophyll a was also determined. The front appears as an enriched region, with chlorophyll concentration and ETS activity higher than in the adjacent waters. Changes in biomass and activity were strongly related to hydrographic conditions. Chlorophyll distributions were mostly influenced by depth, and ETS distribution by differences among the subregions. ETS activity showed a statistically significant correlation with chlorophyll in the whole region and in the three subregions. Depth-integrated ETS activity showed an increase of 62% in frontal versus Mediterranean water, whereas the chlorophyll concentration was only 40% higher, indicating an enhancement of biomass-specific activity. Depth-integrated respiration (estimated from ETS measurement) represents between 30 and 50% of depth-integrated primary production according to published data on this zone.