Briny Biology: Nematodes From the Hypersaline Springs of the Central Namib Desert

Abstract

ABSTRACT Hypersaline environments approach the physiological limits of metazoan life, yet the distribution, abundance, and community structure of animals in such systems remain poorly resolved. Nematodes, which possess remarkable stress tolerance and cryptobiotic capabilities, provide an ideal model for exploring these limits. We investigated nematode communities in sediments and microbial mats from seven hypersaline desert springs in the central Namib Desert, Namibia, spanning nearly a twenty‐fold range in electrical conductivity (EC; 12.3 to > 500 mS cm −1 ). Using live‐extraction methods, we quantified nematode abundance, taxonomic composition, and diversity in relation to spring physicochemical properties. Nematodes were detected in all but four of 84 samples and reached exceptionally high densities (up to 1.6 × 10 5 individuals 100 g −1 dry weight), including in microbial mats in water exceeding 100 mS cm −1 . Contrary to expectations, nematode abundance was not correlated with EC, pH, or dissolved oxygen. However, taxonomic richness declined significantly with increasing EC, indicating environmental filtering of diversity. This impacted mainly rare taxa, and EC was not correlated to the Simpson Index of diversity. Community composition differed among springs and between microbial mats and underlying sediments, with mats supporting higher abundances and distinct assemblages. Multivariate analyses showed that site and substrate type explained substantially more variation in nematode communities than measured physicochemical variables. Communities were characterized by low diversity and dominance of a small number of saline‐tolerant taxa, particularly Monhystrella , which occurred at all sites. Live nematodes were recovered from sediments beneath water with EC > 500 mS cm −1 , suggesting that nematodes can persist under extremely high‐salinity conditions. Our results demonstrate that hypersaline desert springs can support dense but taxonomically simplified nematode communities and highlight microbial mats as key biological structures that buffer extreme conditions and sustain metazoan life.