Microbial communities network structure across strong environmental gradients: How do they compare to macroorganisms?

Abstract

The way strong environmental gradients shape multispecific assemblages has allowed us to examine a suite of ecological and evolutionary hypotheses about structure, regulation, and community responses to fluctuating environments. But whether the highly diverse co-occurring, free-living microorganisms are shaped in similar ways as macroscopic organisms, across the same gradients, has yet to be addressed in most ecosystems. The ‘everything is everywhere’ hypothesis suggests they are not, at least not to the same extent. Here we characterize the structure of intertidal microbial biofilm communities and compare the intensity of zonation at the ‘species’ level, changes in taxonomic diversity and composition at the community level, and network attributes, with those observed in co-occurring macroalgae and invertebrates. At the level of species and OTUs, for dominant macro and microorganisms respectively, microbes showed less variability across the tidal gradient than macroorganisms. At the community-level, however, microbes and macro-organisms showed similarly strong patterns of tidal zonation, with major changes in composition and relative abundances across tides. Moreover, the proportion of ‘environmental specialists’ in different tidal zones was remarkably similar in micro and macroscopic communities, and taxonomic richness and diversity followed similar trends, with lower values in the high intertidal zone. Network analyses showed similar connectivity and transitivity, despite the large differences in absolute richness between the groups. A high proportion of positive co-occurrences within all tidal zones and mostly negative links between the high and low tidal zones were observed among habitat specialist taxa of micro-and macro-organisms. Thus, our results provide partial support to the idea that microbes are less affected by environmental variability than macroscopic counterparts. At the species-level, the most common microbe species exhibit less variation across tides than most common macroscopic organisms, suggesting the former perceive a more homogeneous environment and/or are more resistant to the associated stress. At the community-level, most indicators of community and network structure across the gradient are similar between microbes and macro-organisms, suggesting that despite orders of magnitude differences in richness and size, these two systems respond to stress gradients, giving rise to zonation patterns.

First insights into the gut microbiomes and the diet of the Littorina snail ecotypes, a recently emerged marine evolutionary model

“…There were large differences were between the Crab and the Wave ecotypes; however, there were also differences in microbiomes of the Wave snails from low and high shore. The latter results agree with other studies showing the strong effect of the vertical shore gradients both on environmental bacterial communities and microbiomes of intertidal macro‐organisms (Arboleda‐Baena et al, 2021 ; Weigel & Erwin, 2017 ). This also supports the view that in many aspects, including microbiomes, the Wave ecotype snails should not be regarded as one homogeneous group.…”

“…Vertical zonation on the rocky shores is one of the strongest environmental gradients in the nature and likely to shape the microbiome composition. For example, the tidal zonation has been shown to affect bacterial biofilms on the shores in Chile (Arboleda‐Baena et al, 2021 ) and microbiomes of the sponges living in the subtidal and intertidal (Weigel & Erwin, 2017 ).…”

Unifying microorganisms and macrograzers in rocky shore ecological networks

“…In our study, we introduce a novel protocol for analyzing the cover of epilithic biofilm. This protocol utilizes natural intertidal rocks as the substrate, ensuring a more realistic and reproducible assessment (Protocols.io: dx.doi.org/10.17504/protocols.io.e6nvw5epdvmk/v1) (Arboleda-Baena et al 2023b).…”

“…Our study aimed to uncover the trophic and non-trophic connections between the prevalent intertidal mollusk grazers and the bacterial components of the co-occurring epilithic biofilms (periphyton) ( Fig. 1 ) (Arboleda-Baena et al 2021).…”

Hidden interactions in the intertidal rocky shore: variation in pedal mucus microbiota among marine grazers that feed on epilithic biofilm communities

“…In turn, the less stressful conditions ( i.e. , lower selection pressure) in the lower shore may permit microbiota to differ more widely among grazer species ( Arboleda-Baena et al, 2021 ). A larger variety of species from different shore levels must be investigated to separate effects dependent upon habitat from species-specific effects.…”