{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,4]],"date-time":"2026-02-04T06:30:52Z","timestamp":1770186652211,"version":"3.49.0"},"posted":{"date-parts":[[2026]]},"group-title":"SSRN","reference-count":73,"publisher":"Elsevier BV","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"abstract":"<jats:p>Resolving the spatial organization and taxonomic composition of host-associated microbiomes is fundamental for understanding their roles in host physiology and ecosystem resilience. Animal microbiomes, including diverse bacterial, archaea, and eukaryotes, often vary across geographic regions due to selection, dispersal, and drift. Among the diverse forms of host-microbe symbioses, endolithic microbial communities, which inhabit and corrode calcium carbonate structures of corals, bivalves, and other calcifiers, represent a particularly intriguing, yet understudied component of marine ecosystems. By weakening shells, altering energy budgets, or modulating thermal stress through shell discoloration, they can exert both detrimental and beneficial effects on their hosts. Using high-resolution metabarcoding, we investigated the taxonomic and functional composition of endolithic communities in the intertidal mussel Mytilus galloprovincialis and the oyster Magallana gigas across a biogeographic gradient along the Atlantic coastline. Community composition showed strong biogeographic structuring, with significant regional turnover yet consistent dominance of Cyanobacteria, Proteobacteria, and Bacteroidota, reflecting a mix of widely distributed core taxa alongside locally restricted taxa whose abundances shift across environments. Diversity metrics and FAPROTAX-inferred metabolic profiles also varied geographically, but major functional groups (photoautotrophs, photoheterotrophs, and chemoheterotrophs) remained stable, indicating a conserved functional core. Together, these findings suggest that the bivalve shell provides a relatively stable microenvironment capable of buffering microbial functions against broader environmental gradients.<\/jats:p>","DOI":"10.2139\/ssrn.6174103","type":"posted-content","created":{"date-parts":[[2026,2,3]],"date-time":"2026-02-03T18:41:36Z","timestamp":1770144096000},"source":"Crossref","is-referenced-by-count":0,"title":["Endolithic microbiomes of bivalve shells exhibit strong biogeographic structuring across hosts"],"prefix":"10.2139","author":[{"given":"Sarah","family":"Bollina","sequence":"first","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8798-5794","authenticated-orcid":true,"given":"Gerardo  I.","family":"Zardi","sequence":"additional","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8525-9967","authenticated-orcid":true,"given":"Heliana","family":"Teixeira","sequence":"additional","affiliation":[]},{"given":"Luana","family":"Corona","sequence":"additional","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7071-141X","authenticated-orcid":true,"given":"Katy  R.","family":"Nicastro","sequence":"additional","affiliation":[]}],"member":"78","reference":[{"key":"ref1","author":"D G Adams","year":"2012","journal-title":"Cyanobacterial Symbioses. 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