Comparison of physiological and transcriptome responses of corals to strong light and high temperature.

Coral reefs are essential for marine ecology and biodiversity. Global climate change has resulted in severe coral reef degradation, partly via coral bleaching, which is caused by rising sea temperatures and solar light intensity. In this study, we examined the impact of strong light (300 µmol.m-2.s-1) and high temperature (33°C) on the growth, immunity, and gene expression of Galaxea fascicularis. Strong light caused coral bleaching in the absence of high sea temperatures, while no obvious bleaching was observed under high temperature alone. The effect of strong light on calcification rate of G. fascicularis is significantly weaker than that of high temperature. Both strong light and high temperatures significantly affected the immune enzyme activity of G. fascicularis symbionts, with the former having a strong effect on their photosystem. Temperature affected the digestive system, replication and repair, and cell growth and death of coral hosts, as indicated by transcriptomics analysis. These results provide a valuable for strategies to mitigate coral bleaching. TEASER: We explored the effects of strong light exposure and high temperature on coral reefs and their symbiont algae.

A review of metal contamination in seagrasses with an emphasis on metal kinetics and detoxification.

Seagrasses are important foundation species in coastal ecosystems, and they provide food and habitat that supports high biodiversity. However, seagrasses are increasingly subjected to anthropogenic disturbances such as metal pollution, which has been implicated as a significant factor driving seagrass losses. There have been several reviews synthesizing the metal concentrations in seagrasses and evaluating their utility as biomonitors for metal pollution in the coastal environment at the local scale. However, the interpretation of metal data in seagrass biomonitors requires a more mechanistic understanding of the processes governing metal bioaccumulation and detoxification. In this review, the progress and trends in metal studies in seagrasses between 1973 and 2022 were analyzed to identify frontier topics in this field. In addition, we tried to (1) analyze and assess the current status of metal contamination in seagrasses on a global scale by incorporating more metal data from tropical and Indo-Pacific seagrasses, (2) summarize the geochemical and biological factors governing metal uptake and loss in seagrasses, and (3) provide an up-to-date understanding of metals' effects on seagrasses and their physiological responses to metal challenges. This review improves our understanding of the highly variable metal concentrations observed in the field.

Physiological basis and differentially expressed genes in the salt tolerance mechanism of Thalassia hemprichii.

Seagrass plays a vital role in the stability of marine ecology. The human development of marine resources has greatly affected the survival of seagrass. Seawater salinity is one of the important factors affecting its survival. Seagrass can survive in high saline environments for a long time and has evolved a variety of effective tolerance mechanisms. However, little is known about the molecular mechanisms underlying salinity tolerance by seagrass. Thalassia hemprichii is a seagrass species with a global distribution. It is also an ecologically important plant species in coastal waters. Nevertheless, the continuous environmental deterioration has gradually reduced the ecological niche of seagrasses. In this study, experiments were conducted to examine the effects of salinity changes on T. hemprichii. The result showed that the optimal salinity for T. hemprichii is 25 to 35 PSU. Although it can survive under high and low salinity, high mortality rates are common in such environments. Further analyses revealed that high salinity induces growth and developmental retardation in T. hemprichii and further causes yellowing. The parenchyma cells in T. hemprichii also collapse, the structure changes, soluble sugar accumulates rapidly, soluble proteins accumulate rapidly, the malondialdehyde (MDA) content reduces, and lipid peroxidation reduces in plant membranes. The molecular mechanisms of salt tolerance differ significantly between marine and terrestrial plants. We found 319 differentially expressed genes (DEGs). These genes regulate transport and metabolism, promoting environmental adaptation. The expression of these genes changed rapidly upon exposure of T. hemprichii to salinity stress for three hours. This is the first report on the physiological and biochemical changes and gene expression regulation of T. hemprichii under different salinity conditions. The findings of this study well deepen our understanding of T. hemprichii adaptations to changes in the shoal living environment.

Bacterial epiphyte and endophyte communities of seagrass Thalassia hemprichii: the impact of feed extract solution.

The global seagrass bed ecosystem acts as a natural ecological barrier in the littoral coastal zone. In recent years, this ecosystem has suffered from serious eutrophication and destruction caused by the continuous expansion of aquaculture. However, our understanding of the influence of aquaculture on the bacterial community remains limited. In this study, we used 16S amplicon sequencing to evaluate the impact of aquaculture feed extract solution on the composition and function of bacterial epiphytes and endophyte communities of the core seagrass from the seagrass bed ecosystem in Hainan, Thalassia hemprichii. The feed extract solution was the main factor that significantly affected the bacterial epiphyte and endophyte community structure of seagrass leaves but had no marked effect on alpha diversity was observed. Additionally, the bacterial epiphyte and endophyte community of the T. hemprichii leaves alleviated the effects of organic matter, sulfide, and nutrients caused by aquaculture wastewater. The feed extract solution promoted the proliferation of Bacteroidales, Vibrio, Desulfobulbaceae, Desulfobacteraceae, Pseudoalteromonas, Paludibacter, Marinomonas, and Pseudomonas in the leaves and root of T. hemprichii, which can effectively improve the digestibility of eutrophication. In fact, Desulfobacteraceae and Desulfobulbaceae can reduce sulfate to sulfide and oxidize sulfide to sulfur within seagrass, indicating that the increase in Desulfobulbaceae and Desulfobacteraceae facilitated the accumulation of sulfide with the treatment of feed extract solution, which may be the reason for the degradation of seagrass caused by aquaculture wastewater containing high concentrations of organic pollutants. These results suggest that although seagrass beds can withstand low concentrations of aquaculture pollutants, sulfide emissions should be minimized.

The complete chloroplast genome of Enhalus acodoides and its phylogenetic analysis.

Complete chloroplast genome of Enhalus acodoides was obtained in this work. Circular mapping revealed that the complete chloroplast sequences of E. acodoides was 176,748 bp in length and had an overall GC content of 38.3%, encoded 132 genes which contained 86 protein-coding genes (PCGs), 38 transfer RNA genes (tRNA) and 8 ribosomal RNA genes (rRNA). The phylogenetic tree shows that E. acodoides had a closer relationship with Thalassia hemprichii in Hydrocharitaceae and its analysis will help better understand the evolution of Alismatales species.

Complete mitochondrial genome of the Scorpaenopsis cirrhosa (Scorpaeniformes: Scorpaenidae).

The complete mitochondrial genome of the Scorpaenopsis cirrhosa has been sequenced. The mitochondrial genome is 16 966 bp in length, containing 13 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNA genes, and 1 control region. The gene order and composition of S. cirrhosa mitochondrial genome was similar to that of most other vertebrates. The overall nucleotides base composition of the heavy strand is A (27.91%), G (17.71%), C (28.02%), and T (26.35%). With the exception of the NADH dehydrogenase subunit 6 (ND6) and eight tRNA genes, all other mitochondrial genes are encoded on the heavy strand. The tRNA-Ser2 gene lacked DHC arm and could not fold into a typical clover-leaf secondary structure. Seen from the phylogenetic tree, S. cirrhosa, a stonefish and four rockfishes from the same order (Scorpaeniformes) clustered into one branch.