MEPS 381:199-211 (2009)  -  DOI: https://doi.org/10.3354/meps07862

ABSTRACT: The zooplankton community plays a key role in biological carbon binding activity in the epipelagic marine ecosystem. The activity of the Electron Transport System (ETS), located in the mitochondrial membrane, is a specific and highly sensitive method to determine respiration rates and thus evaluate zooplankton carbon requirements. The present study focuses on the geographical distribution of zooplankton carbon demand and its day/night variability (measured over a 24 h period) in the top 200 m of the water column at 10 sampling stations throughout the Mediterranean Sea, from the Strait of Gibraltar to the Isle of Rhodes. To interpret the ETS data, species composition, abundance, and biomass (in mg wet weight m^–3; mg wet wt m^–3) of zooplankton were investigated. Oxygen consumption (µl O₂ g^–1 h^–1) rates were recalculated for measured in situ temperatures, converted into carbon demand and expressed as µg C g wet wt^–1 d^–1. The carbon requirements per unit zooplankton biomass indicated spatial, geographical and day/night differences in the Mediterranean Sea. The data revealed an increasing gradient from the Strait of Gibraltar to the easternmost station near the Isle of Rhodes, going from a mean value of 240866 to 419344 µg C g wet wt^–1 d^–1. The relationship between zooplankton ETS activity and sea surface temperature was analysed. At all stations, ETS activities, and thus carbon demand, were higher in samples collected between sunset and sunrise than in those collected during daytime. This was related to actively migrating organisms that mediate the vertical transport of material in the sea.

KEY WORDS: Electron Transport System · Oxygen consumption · Carbon consumption · Zooplankton · Mediterranean Sea