Comparative transcriptome analysis reveals changes in gene expression in sea cucumber (Holothuria leucospilota) in response to acute temperature stress.

Ambient temperature is an important abiotic factor that influences growth performance and physiological functions in sea cucumbers. To understand the molecular responses of the sea cucumber Holothuria leucospilota to acute temperature stress, we performed a de novo transcriptome analysis of body wall tissue from H. leucospilota exposed to 2 hoursh of acute heat (35 ± 1 °C) and cold stress (15 ± 1 °C). A total of 99,015 unigenes were obtained after assembly of the sequenced reads. Compared with a control group maintained at 25.0 ± 1 °C, 1169 differentially expressed unigenes (DEGs) were identified after heat stress, 781 were up-regulated and 388 were down-regulated. After cold stress, 1464 DEGs were identified; 900 were up-regulated and 564 were down-regulated. The annotation of DEGs revealed that heat shock proteins play important roles in protecting H. leucospilota from high temperature stress. Furthermore, KEGG pathway enrichment analysis showed that the categories: "Ribosome" and "Protein processing in endoplasmic reticulum" were strongly affected by heat stress. These two pathways are associated with biosynthesis and processing of proteins, and refolding of misfolded proteins. The lipid metabolism pathways "Sphingolipid metabolism" and "Ether lipid metabolism", were affected by cold stress. The RNA-Seq results for eight selected DEGs were verified the expression by quantitative real-time PCR analysis. Our results will improve the understanding of the molecular response mechanisms of H. leucospilota to ambient temperature stress.

Seasonal and spatial variation of protist communities from reef water and open ocean water in patchy coral reef areas of a semi-enclosed bay.

Protists are an important component of the marine ecosystem and play an essential role in material cycle and energy flow, but the distribution of protists in coral reefs have not been fully studied. In this study, high-throughput amplicon sequencing technology was used to study the biodiversity and community structure of protists from coral reefs and open sea areas, with the typical semi-enclosed bay Daya Bay as the research field. There were significant seasonal differences in the dominant phyla of protists, biodiversity index values and ßeta diversity (P < 0.05) but no significant differences in the different sampling areas (P > 0.05). The topological parameters of the co-occurrence network showed the protist co-occurrence network in the open sea had more complex interactions and stronger stability than in the coral reef areas because of the hydrodynamics, waves, and relatively poor nutrients. Redundancy analysis and the Mantel test showed that the structure of the protist community was affected by seawater temperature, pH, salinity, and dissolved oxygen. This study analysed the temporal and spatial differences in protists in the coral reef and open sea areas of Daya Bay to provide important information for the study of protist biodiversity and community structure in semi-enclosed bays.

Response of protist community dynamics and co-occurrence patterns to the construction of artificial reefs: A case study in Daya Bay, China.

Artificial reefs (ARs) are widely used for biodiversity conservation and coastal habitat restoration. Although protists play an important ecological role in marine ecosystems, the response of the protist community to ARs is still poorly understood. In the current study, an Illumina sequencing analysis of 18S rDNA was performed, and the diversity, community structure, and co-occurrence networks of protists in the ARs and open sea area (OW) in Daya Bay were described. The results indicated that significant seasonal differences occur in the seawater protists between the surface and bottom of the ARs and OW. However, the protists in the ARs and OW had different seasonal variations. The ARs always affected the alpha diversity of marine protists in different seasons, while the surface and bottom OW sites had different seasonal effects. The ARs sites had different effects on the community composition of the surface and bottom seawater in different seasons relative to the OW sites. The linear discriminant analysis (LDA) effect size (LEfSe) method showed that 85 biomarkers mainly belonging to 11 taxa, including Bacillariophyta, Chlorophyta, and Dinophyceae, were affected by the ARs (P < 0.05, LDA > 2.0). The ARs played an important role in the seasonal changes in the protist community composition and had different effects on the dominant species of protists in the surface and bottom seawater. A redundancy analysis (RDA) significance test showed that the structure of the protist community in Daya Bay was mainly affected by environmental factors, such as seawater temperature, salinity and dissolved oxygen. Compared with the OW group, the surface and bottom layers of the ARs had more complex protist interactions or more niches. The ARs increased the degree of spatial heterogeneity, which may lead to significant niche differentiation, indicating that ARs as habitat factors affect the complexity and stability of the symbiotic network of protists. The results could provide basic data on the response of the protist community to the ARs in Daya Bay and a reference for assessments of the impact of ARs on the ecological environment.

[Establishing potential habitats of Mytilopsis sallei with Maxent niche model]. / 应用Maxent建立沙筛贝潜在生境模型.

Mytilopsis sallei, an invasive alien species, has strong reproductive ability and high adaptability. It can severely endanger biodiversity of intertidal ecosystem after invasion. The intertidal zones and oyster breeding areas in some coastal areas of Guangdong Province have been severely invaded by M. sallei. To examine the potential habitat of M. sallei in China, we established a potential habitat prediction model of M. sallei using Maxent and ArcGIS method for China and global scales. The model was verified by the method of receiver operating characteristic curve (ROC) analysis and field investigation. The results showed that M. sallei could distribute with high probabili-ty in the area between North and South America, South India in Asia, Sri Lanka, the south coast of the Yangtze River in China, and in Van Dimen Bay of the southern hemisphere. In China, M. sallei mainly distributed in coastal provinces south of Shanghai. The main environmental factors affecting the suitable distribution areas for M. sallei were water vapor pressure, temperature, and solar radiation. After ROC detection, the AUC values of both the training and testing sets were 0.996, indicating that the prediction reached an excellent level. Our results provide theoretical basis for the risk assessment and management of M. sallei, and complement the potential habitat prediction of invasive species in China.