Interstitial meiofauna of Namib sandy beaches

Abstract

Interstitial meiofauna were sampled across the intertidal zone and into the sublittoral region on two exposed sandy beaches on the Namibian coast, Langstrand and Cape Cross. A transverse barrip beach configuration at Langstrand allowed a comparison between the distribution and abundance patterns at the horn and within the bay of the cusp formation on this beach. Of the eight major meiofauna groups, nematodes were widely distributed and always dominant. The crustaceans, harpacticoid copepods and mystacocarids, were prominent in the mid-shore at Cape Cross but occurred in low numbers at Langstrand , where archiannelids were abundant at mid-tide level. Notably high numbers of gastrotrichs (> 1000 per 100 cm³) were found sublittorally at both beaches. Non-selective deposit feeders accounted for at least 58% of those nematodes examined from all stations, suggesting an abundant particulate food supply in coastal waters off South West Africa. Cape Cross supported the highest total meiofauna biomass followed by the Langstrand cusp horn and then cusp bay. A slightly elevated slope over a wide beach face, promoting rapid drainage and optimal oxygenation and food input, appeared as characteristics promoting meiofaunal colonization. These Namibian beaches could mark a zone of decline in the abundance of interstitial meiofauna which, from published work, appears to reach a maximum farther to the south.