Abstract
Assessment of ecosystem health entails consideration of species interactions within and between size classes to determine their contributions to ecosystem function. Elucidating microbial involvement in these interactions requires tools to distil diverse microbial information down to relevant, manageable elements. We used covariance ratios (proportionality) between pairs of species and patterns of enrichment to identify “core communities” of likely interacting microbial (<64 µm), meiofaunal (64 µm to 1 mm) and macrofaunal (>1 mm) taxa within assemblages hosted by a foundation species, the hydrothermal vent tubeworm Ridgeia piscesae. Compared with samples from co-located hydrothermal fluids, microbial communities within R. piscesae assemblages are hotspots of taxonomic richness and are high in novelty (unclassified OTUs) and in relative abundance of Bacteroidetes. We also observed a robust temperature-driven distinction in assemblage composition above and below ~25 °C that spanned micro to macro size classes. The core high-temperature community included eight macro- and meiofaunal taxa and members of the Bacteroidetes and Epsilonbacteraeota, particularly the genera Carboxylicivirga, Nitratifractor and Arcobacter. The core low-temperature community included more meiofaunal species in addition to Alpha- and Gammaproteobacteria, and Actinobacteria. Inferred associations among high-temperature core community taxa suggest increased reliance on species interactions under more severe hydrothermal conditions. We propose refinement of species diversity to “core communities” as a tool to simplify investigations of relationships between taxonomic and functional diversity across domains and scales by narrowing the taxonomic scope.
Highlights
From microbes to megafauna, interactions among species and with their environments shape biological assemblages [1] and, by extension, ecosystem function
Size class congruence and taxonomic covariance Using species and operational taxonomic units (OTUs) counts for the macro, meio and micro size classes from nine grab samples, we explored covariance of species associated with R. piscesae across its range of habitat conditions
Our coordinated analysis of a broad size spectrum of organisms associated with the foundation species Ridgeia piscesae has defined a robust temperature-driven distinction of communities
Summary
Interactions among species and with their environments shape biological assemblages [1] and, by extension, ecosystem function. Coordinated analyses of species-level variation in cohabiting vent fauna and microbes could be used to reveal potentially important interspecies associations beyond microbial-to-faunal food web Sample collection Microbial and faunal assemblages associated with the tubeworm Ridgeia piscesae (Supplementary Fig. 1) were sampled over a range of vent discharge intensities and supporting substrata (basalt and sulphide) using a manipulator arm on the remotely-operated vehicle ROPOS. Tubeworms were removed from the preserved half, and structures and their adhering microbial biofilms [34,35,36] slow the the residue sieved to separate macrofauna (>1 mm) from meiofauna dispersion of hydrothermal fluids and so control physico-chemical gradients for other metazoa and microbes [37] These broad codependencies provide direction for exploring potential functional relationships of micro- and macro-scale community members within the entire assemblage. Taxonomy was assigned to OTUs using the silva_nr_132 reference database [50] for bacteria and archaea and the PR2 v4.11.1 reference
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