Uranium-thorium dating of coral mortality and community shift in a highly disturbed inshore reef (Weizhou Island, northern South China Sea)

Implementing a transformative approach to the coral reefs' recovery phase

Mitigation and rehabilitation are responses to climate change and human misuse. However, many regions worldwide still lose coral reefs even after implementing these responses. We chose Hurghada city, on the Red Sea, and Weizhou island, on the South China Sea, as sample regions to assess their various modes of coral community structure loss against the combined climatic and human impact drivers that led to this shift. Despite the former being considered a regional coral refuge, while the latter was limited, both regions have previously intervened with coral restoration. We found that even after three decades of impact cessation by forcing laws, most coral reef states are still declining (about a third and a half in both cities), have not harnessed the existing crowded larval density, and are unrecovered. Such findings imply that the combined impacts will persist, necessitating a broad connectivity analysis that enables a suitable intervention (hybrid solutions hypothesis). Each state of coral categories was connected to certain combined stressor factors using our broad connectivity analysis to grasp the extent and relative contribution of coral community shift since our data obtained from comparable sites were widely varied. Moreover, destructive emerged changes have transformed the coral community structure under the forced adaptation scenario of the community structure, boosting those who can resist at the expense of others. To prove our hypothesis, we used the connectivity findings in determining the optimal technique and spots for coral rehabilitation around the two cities. We then compared our findings with the outcomes of two other existing adjacent restoration projects related to other endeavors. Our hybrid approach harvested coral larvae that had been wasted in both cities. Thus, hybrid solutions are globally required for such cases, and proper early interventions are needed to maintain the genotype power to boost coral adaptability throw global ecological settings.

The bacterial signature offers vision into the machinery of coral fitness across high-latitude coral reef in the South China Sea

Coral-bacterial interaction is a major driver in coral acclimatization to the stressful environment. 16S rRNA High-throughput sequencing was used to classify the role of different coral reef compartments; sediment, water, and tissue; in the South China Sea (SCS), as well as different locations in shaping the microbial community. The majority of OTUs significantly shifted at impacted sites and indicated distinction in the relative abundance of bacteria compartment/site-wise. Richness and diversity were higher, and more taxa were enriched in the sediment communities. Proteobacteria dominated sediment samples, while Cyanobacteria dominated water samples. Coral tissue showed a shift among different sites with Proteobacteria remaining the dominant Phylum. Moreover, we report a dominance of Chlorobium genus in the healthy coral tissue sample collected from the severely damaged Site B, suggesting a contribution to tolerance and adaptation to the disturbing environment. Thus, revealing the complex functionally diverse microbial patterns associated with biotic and abiotic disturbed coral reefs will deliver understanding of the symbiotic connections and competitive benefit inside the hosts niche and can reveal a measurable footprint of the environmental impacts on coral ecosystems. We hence, urge scientists to draw more attention towards using coral microbiome as a self-sustaining tool in coral restoration.

A Critical Assessment of the Congruency between Environmental DNA and Palaeoecology for the Biodiversity Monitoring and Palaeoenvironmental Reconstruction

The present study suggests that standardized methodology, careful site selection, and stratigraphy are essential for investigating ancient ecosystems in order to evaluate biodiversity and DNA-based time series. Based on specific keywords, this investigation reviewed 146 publications using the SCOPUS, Web of Science (WoS), PUBMED, and Google Scholar databases. Results indicate that environmental deoxyribose nucleic acid (eDNA) can be pivotal for assessing and conserving ecosystems. Our review revealed that in the last 12 years (January 2008–July 2021), 63% of the studies based on eDNA have been reported from aquatic ecosystems, 25% from marine habitats, and 12% from terrestrial environments. Out of studies conducted in aquatic systems using the environmental DNA (eDNA) technique, 63% of the investigations have been reported from freshwater ecosystems, with an utmost focus on fish diversity (40%). Further analysis of the literature reveals that during the same period, 24% of the investigations using the environmental DNA technique were carried out on invertebrates, 8% on mammals, 7% on plants, 6% on reptiles, and 5% on birds. The results obtained clearly indicate that the environmental DNA technique has a clear-cut edge over other biodiversity monitoring methods. Furthermore, we also found that eDNA, in conjunction with different dating techniques, can provide better insight into deciphering eco-evolutionary feedback. Therefore, an attempt has been made to offer extensive information on the application of dating methods for different taxa present in diverse ecosystems. Last, we provide suggestions and elucidations on how to overcome the caveats and delineate some of the research avenues that will likely shape this field in the near future. This paper aims to identify the gaps in environmental DNA (eDNA) investigations to help researchers, ecologists, and decision-makers to develop a holistic understanding of environmental DNA (eDNA) and its utility as a palaeoenvironmental contrivance.

Marine heatwaves impair the thermal refugia potential of marginal reefs in the northern South China Sea

Frequent marine heatwaves (MHWs), concurrent with climate warming, threaten global low-latitude, pristine coral reefs, leading to growing interest in identifying marginal coral reefs (relatively high-latitude and/or turbid reef environments) that can serve as thermal refugia from mass coral bleaching. However, the thermal refugia potential of marginal reefs remains controversial. We evaluated the thermal refugia potential of inshore reefs in the northern South China Sea (nSCS), a globally typical marginal reef system, by characterizing the long-term trend of MHW intensity and frequency and assessing thermal stress during a mass bleaching event in summer 2020. An unprecedented peak intensity of around 20 °C-weeks of cumulative heat stress, associated with a prolonged anomalous western Pacific subtropical high (WPSH) and weakened monsoon activity, induced record-breaking bleaching. The geographical variability of bleaching was strongly related to the extent of heat exposure and satellite-derived temperature anomalies. Under ongoing global warming, the frequency and intensity of MHWs over nSCS coral habitats show a markedly increasing trend, especially during the last decade. Intense MHWs and coral bleaching have already occurred throughout all El Niño-Southern Oscillation (ENSO) phases (e.g., 2010, 2015, and 2020). Climate change has pushed marginal coral reefs to or beyond the limits of their resilience, and frequent MHW events have amplified the increasing risk of thermal stress. There are no long-term thermal refugia for marginal reefs in the nSCS.

Distribution, partitioning behavior and potential source of legacy and alternative per- and polyfluoroalkyl substances (PFASs) in water and sediments from a subtropical Gulf, South China Sea

Legacy per- and polyfluoroalkyl acids (PFASs) have received global concern over the scientific and public community since this century. However, the information on alternative PFASs pollution in the marine environment, especially in the subtropical marine environment is extremely limited. This study investigated the occurrence, partitioning, potential sources, and ecological risks of PFASs, including perfluoroalkane sulfonic acids (PFSAs), perfluoroalkyl carboxylic acids (PFCAs), and alternative PFASs, in surface water and sediments from the subtropical Beibu Gulf, South China. Concentrations of total PFASs (∑PFASs) were in the range of 0.98-2.64 ng/L in water and 0.19-0.66 ng/g (dry weight, dw) in sediment, respectively. Perfluorooctanoic acid (PFOA) was the most abundant PFAS in water, while PFASs in sediment were dominated by perfluorooctanesulfonic acid (PFOS) and PFOA. Among investigated environmental parameters (total organic carbon (TOC), grain size, water pH, sediment pH, and salinity), TOC and salinity were the dominant factors influencing the sediment-water distribution coefficient (K_d) of PFOA, perfluorodecanoic acid (PFDA), and perfluorononanoic acid (PFNA). Log K_d and log soil organic carbon-water distribution coefficient (K_oc) both increase with increasing carbon chain length of PFASs. Significantly positive correlations between PFOS and perfluorohexanoic acid (PFHxA) (p < 0.05), PFOA and perfluoro-1-butane-sulfonamide (FBSA) were observed, suggesting that these PFASs might have similar sources and transport routes. Preliminary environmental risk assessment showed that PFOA and PFOS would not pose risks to the marine aquatic environment. This is the first comprehensive survey of legacy and alternative PFASs in a subtropical area of the Beibu Gulf, which provides significant data and scientific basis to better understand the fate of PFASs and pollution control management.

Turbid Coral Reefs: Past, Present and Future—A Review

Increasing evidence suggests that coral reefs exposed to elevated turbidity may be more resilient to climate change impacts and serve as an important conservation hotspot. However, logistical difficulties in studying turbid environments have led to poor representation of these reef types within the scientific literature, with studies using different methods and definitions to characterize turbid reefs. Here we review the geological origins and growth histories of turbid reefs from the Holocene (past), their current ecological and environmental states (present), and their potential responses and resilience to increasing local and global pressures (future). We classify turbid reefs using new descriptors based on their turbidity regime (persistent, fluctuating, transitional) and sources of sediment input (natural versus anthropogenic). Further, by comparing the composition, function and resilience of two of the most studied turbid reefs, Paluma Shoals Reef Complex, Australia (natural turbidity) and Singapore reefs (anthropogenic turbidity), we found them to be two distinct types of turbid reefs with different conservation status. As the geographic range of turbid reefs is expected to increase due to local and global stressors, improving our understanding of their responses to environmental change will be central to global coral reef conservation efforts.