Effects of carbonic anhydrase inhibition on biomass and primary production of estuarine benthic microalgal communities

Abstract

Recent studies have focused on carbon concentrating mechanisms and the associated enzyme, carbonic anhydrase, to better understand the efficiency of CO2 uptake rates and carbon fixation in photoautotrophs. Some benthic microalgae (BMA) may be limited by inorganic carbon availability because high photosynthetic rates withdraw a large amount of CO2 and HCO3– in the top layer of sediment. Investigating the mechanisms that affect carbon acquisition are necessary if we are to fully understand the functioning and structuring processes of these systems. From this, we can better predict the potential impacts of increasing atmospheric CO2 concentrations on BMA communities. The purpose of this research was to examine a carbon concentrating mechanism used by BMA through their responses to induced carbon limitation. This approach was conducted through the removal of carbonic anhydrase (CA) activity using an inhibitor, ethoxyzolamide. Microcosm experiments were performed on intertidal muddy sediments from North Inlet Estuary, SC. Exposure to ethoxyzolamide resulted in a reduction of gross primary productivity (GPP) without a reduction in total BMA biomass. Furthermore, removed CA activity caused BMA cumulative GPP maxima to shift upward toward the surface in the sediment column. Active CA was necessary to maintain high GPP rates in these communities and allowed motile BMA to use a wider portion of the sediment column. Available HCO3– at lower depths could still be dehydrated into CO2 by microalgae with CA. Changes in global atmospheric CO2 concentrations leading to higher CO2 availability at the atmosphere-sediment interface may alter the structure and function of these BMA systems, and the vertical distribution of GPP. These consequences may have important implications for the biogeochemical cycling occurring in estuaries.