Nitrogenase Activity in Intertidal Sediment Along the Tanzanian Coast, Western Indian Ocean

Abstract

Nitrogenase activity was determined using the acetylene reduction assay in the littoral areas near Tanga, Dar es Salaam and Mafia with the aim of investigating its spatial and temporal distribution along the Tanzanian coastal line. Ethylene (C₂H₄) production rates ranged from 0.07 - 13.5 nmol C₂H₄ cm-²h-¹ in Tanga area, 0.30 - 5.43 nmol C₂H₄ cm-²h-¹ in Dar es Salaam and from 0.10 - 6.25 nmol C₂H₄ cm-²h-¹ in Mafia. Significantly higher rates of nitrogenase activity were measured during night-incubated samples compared to daytime incubated samples suggesting that the sediments were mostly composed of non-heterocystous diazotrophic organisms. However, there were no significant differences in rates of nitrogenase activity between
the rainy and dry season and between the sandy and muddy beaches. Also, there were no
significant differences in nitrogenase activity between the upper, mid and lower littoral zones, and between the three sampling locations, i.e. Tanga, Dar es Salaam and Mafia. A nitrogen fixation rate of 38 mmol N m-²y-¹ was estimated. We conclude that diazotrophs contribute a substantial amount of nitrogen input to the Tanzania coastal ecosystems.

Keywords: Nitrogen fixation, Acetylene Reduction Assay, diazotrophs, intertidal sediment,
Tanzania

West Indian Ocean Journal of Marine Science Vol. 5 (2) 2006: pp. 133-140