041 | Longitudinal characterization of the gut microbiota of Caretta caretta under controlled in-care conditions

Martina Maria Imburgia¹, Fanny Claire Capri, Vincenzo Monteverde, Giorgia Schirò, Rosaria Disclafani, Angelo Costanza, Rosa Alduina, Salvatore Dara, Paola Galluzzo | ¹Centro di Referenza Nazionale sul benessere, monitoraggio, diagnostica delle malattie delle Tartarughe Marine CRetaM, Istituto Zooprofilattico Sperimentale della Sicilia “A. Mirri”, Palermo, Italy; ²Dipartimento di Scienze e Tecnologie Biologiche, Chimiche e Farmaceutiche STEBICEF, Università degli Studi di Palermo, Italy.

Marine turtles (Caretta caretta) represent a sentinel model to explore gut microbiome patterns relevant to anthropogenic pressures on coastal ecosystems within a One Health perspettive [1]. The C.Re.Ta.M (National Reference Center for the welfare, monitoring, and diagnosis of marine turtle diseases), enables serial sampling of individuals during an in-care period and thus the assessment of gut microbiota changes over a defined time window. Here, we conducted a longitudinal analysis of the fecal microbiota came from 20 individuals, sampled at admission (T0) and approximately at 1 month into rehabilitation (T1), in order to describe taxonomic profiles (phylum, family, genus). 16S rRNA gene was amplified and the V3–V4 hypervariable region was sequenced and compared within-individual compositional changes between timepoints. At broader taxonomic ranks, we observed that community structure remained largely conserved, with no uniform cohort-wide shift, consistent with another study [2]. In contrast, genus-level profiling enabled individual-specific patterns; some individuals showed substantial compositional change while others remained relatively stable. These profiles were primarily driven by shifts in the relative abundance of dominant gut-associated genera (e.g., Rikenellaceae RC9, Akkermansia, and Vibrio), with patterns varying across individuals. In juveniles turtles, Rikenellaceae RC9 increased from 8.43 ± 10.81% (T0) to 15.76 ± 7.77% (T1), while Akkermansia decreased from 6.94 ± 11.08% to 0.71 ± 1.11%; conversely, in subadults, Rikenellaceae RC9 decreased from 14.43 ± 13.34% to 6.75 ± 9.27% whereas Akkermansia increased from 0.98 ± 2.35% to 7.13 ± 13.88%, alongside a marked decline in Vibrio (5.63 ± 16.86% and 0.40 ± 0.53%). Importantly, curved carapace length (CCL), serving as a proxy for body size and ontogeny (and ecological traits), was significantly associated with the direction and pattern of changes in community composition over time (p-value 0.044), denoting size-dependent microbiota dynamics across size classes. Furthermore, antibiotic resistance genes (ARGs) were already evident at admission. While no generalized linear association emerged between ARG load and the magnitude of microbiota change across the full cohort, an exploratory extreme-tercile comparison indicated higher within-host turnover in individuals with higher resistome (p-value 0.0428), consistent with a non-linear relationship. Overall, these findings present a view of the gut microbiome of C. caretta during rehabilitation as stable at broader taxonomic ranks yet capable of size-dependent compositional changes at higher resolution. This integrated microbiome–resistome framework can support both health monitoring during recovery and eco-epidemiological surveillance of ecological pressures.
This study was financially supported by the Italian Health Ministry (RC IZSSI 08/23).