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Environmental conditions at different water depths on tropical atolls are substantially different, but few studies have investigated the depth distribution and adaptation in the microbiomes of juvenile and adult corals. We collected samples of juvenile and adult Pocillopora verrucosa from different depths on an atoll in the central South China Sea and analyzed their communities of symbiotic Symbiodiniaceae and associated bacteria. Results showed that the Symbiodiniaceae communities were significantly different at different depths in both juvenile and adult P. verrucosa. Symbiodiniaceae community changed with increasing depth and was dominated by Durusdinium and Cladocopium at 1-m and 20-m depth, respectively. Furthermore, the composition and diversity of Symbiodiniaceae in juvenile and adult corals were different at the same depths. The compositions of associated bacterial communities at different depths also differed significantly between juvenile and adult P. verrucosa. The relative abundance of Endozoicomonas in juvenile and adult P. verrucosa increased with increasing depth, while the Thermus decreased. Our study suggests that juvenile and adult P. verrucosa corals in shallow-water regions associate with high abundances of thermotolerant Symbiodiniaceae and bacteria in the shallow reef flats with high temperature and intense solar radiation, but associate with Symbiodiniaceae and associated bacteria with high photosynthetic efficiency at greater depths. [ABSTRACT FROM AUTHOR]

Sexual reproduction plays an important role in population and community structure maintenance in scleractinian corals, particularly in growth and development after larvae settlement. Despite this, only a few studies have been conducted to monitor the post-settlement growth and development of scleractinian coral larvae. Our study aimed to inform this question by collecting adult Galaxea fascicularis colonies from Weizhou Island (21°00′–21°10′ N, 109°00′–109°15′ E) and recording their early life cycle, from fertilization to recruitment, for one year ex situ. The results demonstrated that G. fascicularis could reproduce sexually when reared in a pond for 2 y. The spawning occurred in April and May, in synchrony with wild corals. Larvae showed association with zooxanthellae 9 d after spawning (4 d after settlement) and completed metamorphosis after 1 month. The mean diameter of G. fascicularis recruits was 4.74 ± 1.12 mm in the first year, which was lower than that reported in the literature for other broadcast corals. The recruits' survival rate decreased continuously every month, with the most severe decline occurring in the second month, from 80.87% to 50.82%. By the end of the first year, the final survival rate was 5.46%, which may be attributed to their competition with algae. This study improved our understanding of the early life cycle of scleractinian corals. [ABSTRACT FROM AUTHOR]

High-latitude coral communities have attracted much attention due to their potential as refuges during global climate change. However, this function is being constrained by the combined pressure of global climate and anthropogenic activities. To determine how the reef has developed, we conducted a long-term monitoring study on coral communities along the Bailong Peninsula in the northern South China Sea. The results showed that the distribution area of corals was 3.67 km2 and that corals extended about 4.7 km along the coastline. The coral distribution pattern is scattered and uneven. Our results showed that the growth of reef-building corals and coral recruitment are improving, indicating that coral recruitment plays an important role in regulating the structure of adult coral populations and promoting the development of coral communities. Bailong Peninsula is expected to become a refuge for corals provided that human activities impacting coral restoration potential are controlled. [ABSTRACT FROM AUTHOR]

As a typical contaminant in fossil fuels, vanadium has undergone dramatically increase due to the impacts from human activities. The excessive anthropogenic vanadium emissions have altered natural geochemical processes. However, research on vanadium geochemistry in the ocean, which is the major sink for vanadium mobilized on land, has lagged much behind relative to those of other contaminants. Here we reconstruct historical patterns of vanadium in surface seawater utilizing a high-resolution temporal record (1984–2015 CE) of geochemical proxies (vanadium/calcium (V/Ca), δ18O, δ13C, etc.) in a Porites coral colony from an offshore non-estuarine island in the northern South China Sea (SCS). We find a close association between the surface winds and the temporal patterns of coral V/Ca ratios, revealing great potential for documenting prehistoric changes in tropical cyclones. Moreover, the coral V/Ca record remarkably captured the temporal patterns of anthropogenic activities, offering a valuable and novel tool for testing the efficacy of specific legislation on pollution prevention. Combined with the other reported coral vanadium data, we recovered the historical changes in vanadium emissions in the northern SCS and identified that changing industrial practices should be responsible for the differences in anthropogenic vanadium emissions at each stage. Our results demonstrated that the coral V/Ca ratio at a high temporal resolution has great potential as a new and direct geochemical proxy for tropical cyclones after removing artificial disturbances in the ocean. [ABSTRACT FROM AUTHOR]

Ecological surveys observe coral "winners" and "losers" in global coral bleaching events. However, the key contributors to holobiont tolerance and interactions between symbionts remain unclear. Herein, we compared bleaching and unbleaching Acropora pruinosa corals from Weizhou Island, during an extreme high-temperature event in the northern South China Sea in 2020. We found the dominant Symbiodiniaceae subclade in the bleaching and unbleaching corals to be C1; however, the density of Symbiodiniaceae in the latter was significantly higher than that in the former. Additionally, the symbiotic bacteria α diversity in the unbleaching coral was significantly higher than that in the bleaching coral, with a reorganized bacterial community structure. Core microbiome analyses revealed 55 bacterial core operational taxonomic units (OTUs), of which 10 were significantly differentially enriched between the two coral groups. The significantly enriched bacterial core OTUs in the unbleaching coral were primarily nitrogen cycling related, while those enriched in the bleaching coral were associated with antimicrobial activity. RNA-Seq analyses revealed that significantly upregulated genes in the bleaching coral were primarily associated with diseases and autophagy, while those in the unbleaching coral were associated with immune defense and maintenance of the symbiotic relationship between corals and symbionts. We propose that the differences in tolerance of A. pruinosa result from the cooperation between coral host, Symbiodiniaceae, and symbiotic bacteria. In extreme high-temperature events, unbleaching corals may maintain stable symbiotic relationships by increasing the diversity of symbiotic bacteria, regulating the structure of the symbiotic bacteria community, improving the interaction between coral host and symbiont and enhancing host immunity, thus avoiding coral bleaching. This study illuminates the relationship between the coral symbiont and tolerance differences of coral holobionts, providing new insights for further exploration into the adaptability of scleractinian corals in the context of global warming. [ABSTRACT FROM AUTHOR]