Respiratory ETS activity of plankton in the northwestern Alboran Sea: seasonal variability and relationship with hydrological and biological features

Abstract

Respiratory electron transport system (ETS) activity was measured in plankton samples (<200 μm) collected in the NW Alboran Sea. Sampling was carried out during seasonal cruises (summer and autumn 2003 and winter and spring 2004) in 12 stations located in transects off the coast of Malaga (southern Spain). This work reports for the first time seasonal variations of the Arrhenius activation energy (Ea) as well as being the first study to address CO₂ balance in the NW Alboran Sea. These variations were related to changes in the phytoplankton community assemblage, which could ultimately be caused by the seasonal variability of hydrological conditions. ETS activity was significantly higher in summer, coinciding with a higher chlorophyll a (Chl a) concentration and relatively high levels of particulate organic matter. The ETS:Chl a_total ratios were low during the four seasons, suggesting a high contribution of autotrophic phytoplankton to the respiratory activity of planktonic community. Respiratory CO₂ production (RCP) calculated from ETS activity ranged from 4.6 to 28.1 mg C m⁻³ day⁻¹ during the four cruises. Chl a-specific RCP was lower than the maximum photosynthetic rates reported in the literature for the studied area, suggesting that primary production (PP) and respiration in the water column might be unbalanced.