Synecological response of desert spring benthic prokaryotes and macroinvertebrates to Sierra Nevada roof pendant-derived calcium

Despite the ecological significance of desert springs, little is known about relationships between spring hydrogeochemistry and ecology, particularly over multiple trophic levels. Here, we surveyed microbial communities (bacteria and archaea) and benthic macroinvertebrate (BMI) communities in springs that recharge through granitoid rocks in Owens Valley, CA, to determine whether subtle geochemical differences imparted by Paleozoic roof pendant weathering in the source area affects spring ecosystems. Relative to other springs, roof pendant-recharged springs were characterized by elevated: (i) Ca2+/Na+, Ca2+/Mg2+, and divalent/monovalent cation ratios, (ii) relative abundance of benthic aerobes/facultative anaerobes and holdfast/stalked bacteria, and (iii) abundance and diversity of shredder and collector-gatherer BMIs. These BMI feeding groups graze on biofilm communities and stimulate bacterial degradation of particulate organic matter, consistent with extensive bacteria-BMI connections in co-occurrence networks of these springs. Springs not impacted by roof pendants were instead enriched with anaerobes and chemolithotrophs and low-diversity BMI communities with poor bacteria-BMI network connectivity. We speculate that excess Ca2+ derived from roof pendant weathering plays a key role in biofilm formation on coarse granite substrates, with subsequent synergy between benthic microbial biofilms and diverse BMI shredders/collector-gatherers to degrade allochthonous organic material.