Influence of Oxygen Minimum Zone on Macrobenthic Community Structure in the Northern Benguela Upwelling System: A Macro-Nematode Perspective

Abstract. Macrobenthic samples were collected offshore Namibia on board R/V Mirabilis during the 3^rd RGNO training and the National Marine Information and Research Centre's (NatMIRC's) plankton survey from 13^th May to 17^th May 2016. Two transects, Cape Frio (20º S) and Walvis Bay (23º S), hosted three stations each, while the third transect, Luderitz (26º S), hosted only one station. From the results, three oxygen zones were identified, namely Microxic (< 0.1 ml l⁻¹), Dysoxic (0.1–1.0 ml l⁻¹), and Oxic (> 1.0 ml l⁻¹). A total of 20 Macrobenthic taxa were identified; Nematoda, Polychaeta, Cumacea, and Oligochaeta were the most dominant taxa and recorded abundances in all oxygen zones. Eighteen genera of macro-Nematoda were identified; Desmolaimus and Paracomesoma dominated in all oxygen zones, Metoncholaimus recorded higher abundance in the Dysoxic stations, and no abundance in the Oxic stations, and the opposite was observed for Halanonchus and Dorylaimopsis. H′ Diversity values for both the general Macrofauna and Macro-Nematoda were higher in the Oxic stations and lower in both the Dysoxic and Microxic stations, while an opposite trend was observed for Dominance values. Density values were lower in Microxic stations and higher in Dysoxic stations, while at the Oxic stations, the density values fell in between the two hypoxic zones.