The Hidden Oases: Unveiling Trophic Dynamics in Namib's Fog Plant Ecosystem

Abstract The Namib Desert is a hyperarid coastal desert where fog is a major moisture source. We hypothesized that the fog-harvesting grass Stipagrostis sabulicola establishes an important ecological niche in the extreme Namib Sand Sea ecosystem, referred to as "Fog-Plant-Oases (FPO)". Using a combination of extraction methods, we collected and described the above- and belowground FPO invertebrate communities and inferred their trophic feedings based on stable carbon and nitrogen isotope values. Our findings revealed a complex trophic structure and a unique food web, all of which revolve around a single fog plant as the primary producer. We demonstrated that S. sabulicola serves as the primary energy source for the aboveground food web, encompassing a diverse range of trophic levels. Nevertheless, the distinctive stable isotope values of bacterial- and fungal-feeding nematodes indicated the separation of the aboveground niche, which is primarily sustained by S. sabulicola, from the belowground niche, where wind-blown sediments serve as the main energy source. These findings further accentuate the role of S. sabulicola not only as a primary producer but also as a source of moisture and habitat provider for belowground invertebrates.