The bivalve Lembulus bicuspidatus may enhance denitrification in shelf sediment at the Angola–Benguela Frontal Zone

We collected living individuals of the bivalve Lembulus bicuspidatus , which shows an unusual preference for the oxygen-deficient habitat found at the Angola–Benguela Frontal Zone of the southeastern Atlantic. With a series of incubation experiments with 15 N-labelled nitrate as a tracer in combination with membrane-inlet mass spectrometry, we studied the potential contribution of L. bicuspidatus to nitrate reduction in the upper sediment layer. Our preliminary results suggest that L. bicuspidatus enhances nitrate reduction if the oxygen concentration is sufficiently low. The Lembulus -mediated nitrate reduction rate is then similar to the rate of microbial nitrate reduction in the surrounding sediment. Keywords: Benguela upwelling system, hypoxic bottom water, isotope-pairing, macrozoobenthos, membrane-inlet mass spectrometry, nitrate reduction, oxygen minimum zone