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Blue carbon can be transferred from primary producers to primary consumers through oyster filter feeding. Understanding the carbon (food) sources is crucial for understanding coastal food webs and management of oyster aquaculture ecosystems. In the present study, Bayesian stable isotope mixing models (MixSIAR) were used to identify and quantify food composition within a cultured oyster ecosystem at six sites along a salinity gradient in the estuarine bay of Zhenhai (ZHB). The carbon stable isotope (δ13C) signatures of oyster Crassostrea hongkongensis ranged from −22.06 to −27.27‰, with significant spatial differences (p < 0.001), indicating variations in food resources along the salinity gradient. The primary food source for cultured oysters was suspended particle organic matter across ZHB (55.7–90.6%), with sedimentary organic matter contributing more in the mid-estuary (28.9–44.3%). Partial least squares regression (PLSR) was used to explore the effects of habitat environment and human disturbance on spatial variation in oyster diets. The results indicated that dissolved oxygen, sediment particle size, elevation, and mangrove-related landscape indices were the main factors influencing oyster diet in ZHB. The findings provide insights into the dietary composition of cultured oysters and the underlying factors in a typical shallow bay in southern China, with particular emphasis on the role of terrestrial landscape features. In addition, the findings validate PLSR as a reasonable tool for predicting the food composition of consumers in estuarine bays. • Providing the carbon isotope data in a typical oyster culture region of South China. • The MixSIAR model was employed to quantify the spatial distribution of oyster diets. • Food resources of cultured oysters changed spatially along the salinity gradient. • Coastal land use patterns in aquaculture areas could influence oyster diets. • Managing oyster aquaculture production using partial least squares regression. [ABSTRACT FROM AUTHOR]

Naked carp (Gymnocypris przewalskii) is a migratory fish endemic to the Qinghai Lake, the largest inland saline-alkaline lake in China. Based on our previous results of comparative transcriptome sequencing, we found that pathways related to regulation of actin cytoskeleton, plasma membrane damage, and inflammation-related signaling were significantly enriched during saline-alkaline stress, suggesting involvement of annexin (ANN) family proteins in stress adaption in naked carp. Herein, to explore the role of annexin family in naked carp under saline-alkaline stress, twenty GpANNs family members were identified at the genome-wide scale, and bioinformatics and expression analysis under saline-alkaline stress were performed. The predicted subcellular localization showed that most members of GpANNs were distributed in the cytoplasm, and the rest were localized in the cytoskeleton, nucleus, or mitochondria, respectively. GpANNs family proteins contained specific type II Ca2+-binding motifs, actin-binding motifs, GTP-binding motifs, etc. Phylogenetic tree analysis showed that the annexin homologues from naked carp, carp (Cyprinus carpio), zebrafish (Danio rerio), and chinese cavefish (Sinocyclocheilus rhinocerous) were divided into eight groups, i.e. ANN1 ∼ 6, ANN11 and ANN13. But homologues of ANN7 ∼ 10 groups were not found in these three fish species. Twenty-eight, nineteen and twenty-nine orthologous gene pairs were identified between naked carp and carp, zebrafish and chinese cavefish, respectively. Six paralogous gene pairs were identified in naked carp, all of which had a Ka/Ks ratio less than one, suggesting that the GpANNs family may have undergone purifying selection pressure during evolution. Expression of GpANN3 was significantly up-regulated in the kidney tissue under saline-alkaline stress, while GpANN2 was significantly down-regulated. Similar trends of protein expression were also observed by Western blot, suggesting involvement of GpANN3 and GpANN2 in stress response. Confocal microscopy revealed that GpANN2 was localized in both cytoplasm and nucleus, but GpANN3 was preferentially localized in the cytoplasm. Our study demonstrated the role of annexins in stress adaption, and provided the basic information required for further function analyses in naked carp. • The annexin family were comprehensively analyzed in G. przewalskii for the first time, but ANN7 ∼ 10 memebers were lacked. • GpANNs contain a variety of motifs which may be important sites for protein function under saline-alkaline conditions. • GpANNs exhibited differential expression patterns in 12 different tissues under saline-alkaline stress. • In kidney, GpANN2 and GpANN3 significantly responded to saline-alkaline stress at both mRNA and protein levels. [ABSTRACT FROM AUTHOR]