Estivation is a widespread survival strategy for dealing with adverse environmental conditions such as high temperature, low oxygen and lack of water or food, which has been reported across multiple vertebrate and invertebrate species. The sea cucumber Apostichopus japonicus is an excellent model organism to investigate the adaptive mechanism of estivation in marine invertebrates. In this study, a metabolomics approach based on ultraperformance liquid chromatography coupled with electrospray ionization time-of-flight mass spectrometry (UPLC-ESI-Q-TOF/MS) was performed to reveal the metabolic response of intestines from adult A. japonicus over the annual estivation-arousal cycle: nonestivation (NA), deep-estivation (DA) and arousal from estivation (AA). A total of 424 metabolites were identified, and among them, 243, 238 and 37 significant differentially metabolites (DMs) were further screened in the comparisons of DA vs. NA, AA vs. DA, and AA vs. NA. Specifically, the levels of metabolites involved in glycolysis and the tricarboxylic acid cycle were significantly decreased, while higher amounts of long-chain fatty acids, phospholipids and free amino acids were found in A. japonicus during estivation, implying that sea cucumbers might reorganize metabolic priorities for ATP production by depressing carbohydrate metabolism and promoting lipid and amino acid catabolism. Interestingly, elevated relative carbon flow entry into the pentose phosphate pathway and accumulation of various nonenzymatic antioxidant molecules (e.g., tocotrienols, folic acid, catechin, genistein and resveratrol) were observed in estivating sea cucumbers, which suggested that enhancement of the reactive oxygen species defense system might promote long-term viability in the hypometabolic state in an energy-efficient manner. Thus, this research provides new insights into the adaptation mechanisms of marine invertebrates to estivation at the metabolic level.

Seagrass meadows are important marine ecosystems in coastal areas, offering ecological and economic services to the mankind. However, these ecosystems are facing declines due to climate changes and human activities. Rhizosphere-associated microbiomes play critical roles in the survival and adaptation of seagrasses. While prior studies have explored the general microbial communities and their roles in seagrass meadows, there is a gap in understanding the specific rhizosphere microbiomes of different seagrass species and their interdependent relationships. Our study analyzed the microbial community composition and their metabolism in the rhizosphere of Ruppia sinensis (RS), Zostera japonica (ZJ), and Zostera marina (ZM) obtained from the coastal area of Shandong, China, using high throughput and metagenome sequencing. We found that Rhodobacteraceae, Desulfocapsaceae, and Sulfurovaceae were enriched in RS, ZJ, and ZM samples, respectively, compared with the other two seagrass species, and the bacterial connections were decreased from RS to ZM and ZJ samples. The abundances of nirKS and norBC , mediating denitrification, were higher in RS samples with 2.38% ± 0.59% and 2.14% ± 0.24%, respectively. RS samples also showed a higher level of genes in assimilatory sulfate reduction but lower levels in dissimilatory sulfate reduction and oxidation, with a greater ability to convert sulfide into L-cysteine and acetate. Metagenome-assembled genomes from metagenome of RS rhizosphere had a higher diversity and were assigned to eight phyla. Our study could provide a typical project to analyze the bacterial community structures and metabolic functions in the rhizosphere microbiomes of different seagrasses. IMPORTANCE: Seagrasses are indispensable in marine ecosystems, offering numerous critical services, with their health significantly influenced by associated rhizosphere microbiomes. Although studies have investigated the microbial communities and their ecological roles in seagrass meadows, the correlations between rhizosphere microbiome and seagrass species from a particular geographic region are limited. Some studies concentrated on the bacterial composition within the rhizosphere of various seagrasses, but the functional aspects of these microbiomes remain unexplored. Our research delves into this void, revealing that Ruppia sinensis , Zostera japonica , and Zostera marina host diverse bacterial community in the composition, connections, functions, and metabolism, such as nitrogen and sulfur metabolism. Our study revealed that seagrass species play an important role in shaping the rhizosphere microbiomes in an equivalent environment, emphasizing the importance of seagrass species in shaping the rhizosphere microbial communities.

Ocean acidification (OA) and ocean warming (OW) are potential obstacles to the survival and growth of marine organisms, particularly those that rely on calcification. This study investigated the single and joint effects of OA and OW on sea cucumber Apostichopus japonicus larvae raised under combinations of two temperatures (19 °C or 22 °C) and two pCO₂ levels (400 or 1000 μatm) that reflect the current and end-of-21st-century projected ocean scenarios. The investigation focused on assessing larval development and identifying differences in gene expression patterns at four crucial embryo–larval stages (blastula, gastrula, auricularia, and doliolaria) of sea cucumbers, using RNA-seq. Results showed the detrimental effect of OA on the early development and body growth of A. japonicus larvae and a reduction in the expression of genes associated with biomineralization, skeletogenesis, and ion homeostasis. This effect was particularly pronounced during the doliolaria stage, indicating the presence of bottlenecks in larval development at this transition phase between the larval and megalopa stages in response to OA. OW accelerated the larval development across four stages of A. japonicus, especially at the blastula and doliolaria stages, but resulted in a widespread upregulation of genes related to heat shock proteins, antioxidant defense, and immune response. Significantly, the negative effects of elevated pCO₂ on the developmental process of larvae appeared to be mitigated when accompanied by increased temperatures at the expense of reduced immune resilience and increased system fragility. These findings suggest that alterations in gene expression within the larvae of A. japonicus provide a mechanism to adapt to stressors arising from a rapidly changing oceanic environment.