Taxonomic composition and functional potentials of gastrointestinal microbiota in 12 wild-stranded cetaceans.

Cetaceans play a crucial role in marine ecosystems; however, research on their gastrointestinal microbiota remains limited due to sampling constraints. In this study, we collected hindgut samples from 12 stranded cetaceans and performed 16S rRNA gene amplicon sequencing to investigate microbial composition and functional potentials. Analysis of ZOTUs profiles revealed that the phyla Firmicutes, Proteobacteria, and Bacteroidetes dominated all hindgut samples. However, unique microbial profiles were observed among different cetacean species, with significant separation of gut microbiota communities according to biological evolutionary lineages. Different genera that contain pathogens were observed distinguishing delphinids from physeteroids/ziphiids. Delphinid samples exhibited higher abundances of Vibrio, Escherichia, and Paeniclostridium, whereas physeteroid and ziphiid samples showed higher abundances of Pseudomonas, Enterococcus, and Intestinimonas. Functional analysis indicated convergence in the gut microbiota among all cetaceans, with shared bacterial infection pathways across hindgut samples. In addition, a comparison of the gastrointestinal microbial composition between a stranded short-finned pilot whale (Globicephala macrorhynchus) and a stranded rough-toothed dolphin (Steno bredanensis) using 16S rRNA gene sequencing revealed distinct microbial community structures and functional capacities. To the best of our knowledge, this study represents the first report on the gastrointestinal microbiota of the pantropical spotted dolphin (Stenella attenuata), Blainville's beaked whale (Mesoplodon densirostris), and rough-toothed dolphin, with various comparisons conducted among different cetacean species. Our findings enhance the understanding of microbial composition and diversity in cetacean gastrointestinal microbiota, providing new insights into co-evolution and complex interactions between cetacean microbes and hosts.

Geographic and tissue-specific variations of the trace elements and trophic niches of three offshore cetaceans in Chinese waters.

Systematical investigation on trace elements' (TEs) distribution and trophic niches of cetaceans are essential to understand marine mammal ecology and environmental toxicology. Here, the concentrations of 10 TEs and isotopic values in six tissues of stranded Stenella attenuata (SA) and Kogia breviceps (KB) from the northern South China Sea (SCS) and Peponocephala electra (PE) from the East China Sea (ECS) were investigated. The TEs levels of the studied cetaceans were characterized by geo- and tissue-specific distributions. For SA and KB, most TEs levels were in the normal ranges, with low toxicological risk. For PE, several toxic TEs accumulated above the thresholds up to 892.80 µg/g of Hg and 335.24 µg/g of Cd, indicating that land-based anthropogenic pollution may be an ongoing threat to top predators in the ECS. The liver, spleen, and kidney are the main organs that accumulate toxic TEs, and there are strong positive, such as Se-Hg, correlations in several tissues. In particular, for PE with severe Hg and Cd exposure, tissue-specific distribution and correlations were more obvious. The results of stable carbon and nitrogen isotopes showed partly overlapped trophic niches of the three cetaceans, with similar calculated trophic levels in a narrow range of 4.29-4.43.