Epiphytic cryptogam communities differ little despite strong variation in coastal fog exposure

Because mosses and lichens obtain water directly from their surroundings, coastal fog is expected to strongly influence epiphytic cryptogam communities during the long summer droughts of Mediterranean-climate ecosystems. We examined epiphytic mosses and lichens on coyote brush (Baccharis pilularis) across coastal and inland transects on San Bruno Mountain, California, where marine-layer exposure produces a sharp local microclimate gradient. We surveyed coyote brush availability, sampled standardized branches, monitored temperature and relative humidity, and quantified cryptogam occurrence, diversity, morphology, and reproduction. Morphological and chemical identifications were supplemented with molecular markers, while bacterial 16S sequencing was used to characterize cryptogam-associated microbiomes across host taxa and, for the dominant moss Pulvigera pringlei, across transects. Coastal microsites were cooler and more humid, whereas inland microsites experienced substantially greater daytime atmospheric drying demand. Despite this pronounced environmental contrast, cryptogam abundance, reproduction, and visible community composition differed little between transects, although branch-level genus diversity was modestly higher on the coastal transect. Macrolichen lobe or branch length and cryptogam patch area were greater inland in pooled comparisons, but these differences weakened after accounting for taxonomic composition. Bacterial communities differed strongly among cryptogam host taxa, but the P. pringlei microbiome showed no detectable difference in diversity or composition between coastal and inland transects. The broad similarity of cryptogam communities across a strong fog gradient is consistent with buffering of epiphytic cryptogams against fine-scale variation in marine-layer exposure. For the predominantly green-algal lichens in this community, the ability to absorb water vapor from humid air may reduce dependence on direct fog wetting, while host-associated bacterial communities may be structured more strongly by host identity than by local microclimate. Together, our results show that epiphytic cryptogam communities and microbiomes can remain remarkably similar across pronounced microclimatic variation despite modest morphological shifts.