Diversity and seasonal occurrence of haptophyta in northern South China Sea through size-fractionated metabarcoding.

Haptophyta plays a key role in marine pico-nanoeukaryote communities but information on their diversity and ecology is extremely limited. A total of 103 water samples were collected in northern South China Sea to assess the diversity of haptophyta through metabarcoding targeting 18S V4 rDNA. Furthermore, we investigated the potential genetic differentiation among seasonal occurring Phaeocystis globosa using the high resolution molecular marker pgcp1. 18S V4 rDNA metabarcoding dataset revealed 41 species of haptophytes, with 16 of them as the first record in this region. Notably, six harmful species were detected, including Chrysochromulina leadbeateri, Phaeocystis globosa, and Prymnesium parvum. The pgcp1 marker revealed two clades of Phaeocystis globosa and both of them were present around the year. Clade I was found to predominate in warm season, while Clade III tended to bloom in cold waters. Our results highlight the risk potential of harmful haptophytes in the northern South China Sea.

Linking coral fluorescence phenotypes to thermal bleaching in the reef-building Galaxea fascicularis from the northern South China Sea.

Coral fluorescence phenotypes have been suggested as an adaptation to a broad range of environmental conditions, yet the mechanisms linking thermal bleaching tolerance in reef-building coral populations, associated with fluorescence phenotypes due to GFP-like proteins, remains unclear. In this study, the relationship between the thermal sensitivity and phenotypic plasticity of corals was investigated using two phenotypes of Galaxea fascicularis, green and brown. The results reveal that brown G. fascicularis was more susceptible to bleaching than green G. fascicularis when exposed to a higher growth temperature of 32 °C. Both phenotypes of G. fascicularis were associated with the thermotolerant Symbiodiniaceae symbiont, Durusdinium trenchii. However, the brown G. fascicularis showed a significant decrease in Symbiodiniaceae cell density and a significant increase in pathogenic bacteria abundance when the growth temperature was raised from 29 to 32 °C. The physiological traits and transcriptomic profiles of Symbiodiniaceae were not notably affected, but there were differences in the transcriptional levels of certain genes between the two phenotype hosts of G. fascicularis. Under heat stress of 32 °C, the gene encoding green fluorescent protein (GFP)-like and chromosome-associated proteins, as well as genes related to oxidative phosphorylation, cell growth and death showed lower transcriptional levels in the brown G. fascicularis compared to the green G. fascicularis. Overall, the results demonstrate that the green form of G. fascicularis is better able to tolerate ocean warming and defend against pathogenic bacteria, likely due to higher gene transcription levels and defense ability. Supplementary Information: The online version contains supplementary material available at 10.1007/s42995-023-00190-1.

Critical factors driving spatiotemporal variability in the phytoplankton community structure of the coral habitat in Dongshan Bay, China.

This study investigated the spatiotemporal distribution of the phytoplankton in the coral habitat of Dongshan Bay (China), along with critical factors affecting the distribution, during June, August, and December 2022. Phytoplankton abundance in Dongshan Bay exhibited considerably temporal variation, peaking in June 2022, gradually decreasing thereafter, and reaching its lowest point in December 2022. The abundance of bottom-layer phytoplankton consistently exceeded that of the surface layer throughout all seasons. The average phytoplankton abundance in the coral habitat of Dongshan Bay was lower than that in non-coral habitat areas. Fluctuations in the Zhangjiang River and coastal upwelling influenced the diversity and community structure of the phytoplankton. Critical factors causing spatiotemporal variability in phytoplankton community structure included nutrient concentrations and seawater temperature. Nutrients played key roles in influencing various phytoplankton groups. Dominant diatom species, such as Thalassionema nitzschioides and Thalassiosira diporocyclus, were positively correlated with ammonia nitrogen, seawater salinity, coral cover, and the number of coral species present. In winter, Calanus sinicus exhibited a negative correlation with harmful algal bloom species. Additionally, it was found that both in the coral habitat and surrounding open sea, currents, nutrients, and zooplankton may play crucial roles in determining the spatiotemporal variability in the phytoplankton community structure.

Lineage-specific symbionts mediate differential coral responses to thermal stress.

BACKGROUND: Ocean warming is a leading cause of increasing episodes of coral bleaching, the dissociation between coral hosts and their dinoflagellate algal symbionts in the family Symbiodiniaceae. While the diversity and flexibility of Symbiodiniaceae is presumably responsible for variations in coral response to physical stressors such as elevated temperature, there is little data directly comparing physiological performance that accounts for symbiont identity associated with the same coral host species. Here, using Pocillopora damicornis harboring genotypically distinct Symbiodiniaceae strains, we examined the physiological responses of the coral holobiont and the dynamics of symbiont community change under thermal stress in a laboratory-controlled experiment. RESULTS: We found that P. damicornis dominated with symbionts of metahaplotype D1-D4-D6 in the genus Durusdinium (i.e., PdD holobiont) was more robust to thermal stress than its counterpart with symbionts of metahaplotype C42-C1-C1b-C1c in the genus Cladocopium (i.e., PdC holobiont). Under ambient temperature, however, the thermally sensitive Cladocopium spp. exhibited higher photosynthetic efficiency and translocated more fixed carbon to the host, likely facilitating faster coral growth and calcification. Moreover, we observed a thermally induced increase in Durusdinium proportion in the PdC holobiont; however, this "symbiont shuffling" in the background was overwhelmed by the overall Cladocopium dominance, which coincided with faster coral bleaching and reduced calcification. CONCLUSIONS: These findings support that lineage-specific symbiont dominance is a driver of distinct coral responses to thermal stress. In addition, we found that "symbiont shuffling" may begin with stress-forced, subtle changes in the rare biosphere to eventually trade off growth for increased resilience. Furthermore, the flexibility in corals' association with thermally tolerant symbiont lineages to adapt or acclimatize to future warming oceans should be viewed with conservative optimism as the current rate of environmental changes may outpace the evolutionary capabilities of corals. Video Abstract.

Particle manipulation with twisted circle Pearcey vortex beams.

In this Letter, we present an approach for particle manipulation utilizing twisted circle Pearcey vortex beams. These beams are modulated by a noncanonical spiral phase, which allows for flexible adjustment of rotation characteristics and spiral patterns. Consequently, particles can be rotated around the beam's axis and trapped with a protective barrier to avoid perturbation. Our proposed system can quickly de-gather and re-gather multiple particles, enabling a swift and thorough cleaning of small areas. This innovation opens up new possibilities in particle cleaning and creates a new platform for further study.

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.

Identification of quorum sensing-regulated Vibrio fortis as potential pathogenic bacteria for coral bleaching and the effects on the microbial shift.

Coastal pollution, global warming, ocean acidification, and other reasons lead to the imbalance of the coral reef ecosystem, resulting in the increasingly serious problem of coral degradation. Coral bleaching is often accompanied by structural abnormalities of coral symbiotic microbiota, among which Vibrio is highly concerned. In this study, Vibrio fortis S10-1 (MCCC 1H00104), isolated from sea cucumber, was used for the bacterial infection on coral Seriatopora guttatus and Pocillopora damicornis. The infection of S10-1 led to coral bleaching and a significant reduction of photosynthetic function in coral holobiont, and the pathogenicity of V. fortis was regulated by quorum sensing. Meanwhile, Vibrio infection also caused a shift of coral symbiotic microbial community, with significantly increased abundant Proteobacteria and Actinobacteria and significantly reduced abundant Firmicutes; on genus level, the abundance of Bacillus decreased significantly and the abundance of Rhodococcus, Ralstonia, and Burkholderia-Caballeronia-Paraburkholderia increased significantly; S10-1 infection also significantly impacted the water quality in the micro-ecosystem. In contrast, S10-1 infection showed less effect on the microbial community of the live stone, which reflected that the microbes in the epiphytic environment of the live stone might have a stronger ability of self-regulation; the algal symbionts mainly consisted of Cladocopium sp. and showed no significant effect by the Vibrio infection. This study verified that V. fortis is the primary pathogenic bacterium causing coral bleaching, revealed changes in the microbial community caused by its infection, provided strong evidence for the "bacterial bleaching" hypothesis, and provided an experimental experience for the exploration of the interaction mechanism among microbial communities, especially coral-associated Vibrio in the coral ecosystem, and potential probiotic strategy or QS regulation on further coral disease control.

Deciphering pH-dependent microbial taxa and functional gene co-occurrence in the coral Galaxea fascicularis.

How the coral microbiome responds to oceanic pH changes due to anthropogenic climate change, including ocean acidification and deliberate artificial alkalization, remains an open question. Here, we applied a 16S profile and GeoChip approach to microbial taxonomic and gene functional landscapes in the coral Galaxea fascicularis under three pH levels (7.85, 8.15, and 8.45) and tested the influence of pH changes on the cell growth of several coral-associated strains and bacterial populations. Statistical analysis of GeoChip-based data suggested that both ocean acidification and alkalization destabilized functional cores related to aromatic degradation, carbon degradation, carbon fixation, stress response, and antibiotic biosynthesis in the microbiome, which are related to holobiont carbon cycling and health. The taxonomic analysis revealed that bacterial species richness was not significantly different among the three pH treatments, but the community compositions were significantly distinct. Acute seawater alkalization leads to an increase in pathogens as well as a stronger taxonomic shift than acidification, which is worth considering when using artificial ocean alkalization to protect coral ecosystems from ocean acidification. In addition, our co-occurrence network analysis reflected microbial community and functional shifts in response to pH change cues, which will further help to understand the functional ecological role of the microbiome in coral resilience.

Biofriendly Waste Shell Powders/Polylactic Acid Composites for Antibacterial Engineering Applications.

With the rapid progress of agriculture and aquaculture, waste shells are harming the environment because of large production, and highly valued recycling is now holding more attention. However, there are still no good ways for simultaneously solving the poor mechanical and antibacterial performance during the recycling process. In this work, antibacterial shell-grafting-Ag powders/polylactic acid (shell-g-Ag/PLA) biocompatible composites, with comparable mechanical properties to industrial polymer counterparts, were prepared via the in situ reduction of Ag ions on surfaces of polydopamine-modified shell powders. The introduction of Ag particles increases the compatibility on the interface and endows the composites with antibacterial performance by inheriting the prominent characteristic from Ag. Without scarifying the mechanical properties by improving the crystallinity and interface, the loaded Ag particles in the composites endowed the composites with valorized antibacterial performance, evidenced by a bacterial inhibition width from 0 to ∼3.29 mm. The biofriendly composites, together with comparable mechanical properties to industrial PLA products, can serve as a sustainable material to be applied in the field of disposable packaging.

Rigid, eco-friendly and superhydrophobic SiO2-Polyvinyl alcohol composite sponge for durable oil remediation.

Development of durable and eco-friendly adsorbents for oil remediation is in great demands. However, most of adsorbents were designed to pursue large capabilities while ignored their strength after adsorbing oil, which might cause secondary oil spilling during complex salvage process. Herein, an eco-friendly and superhydrophobic SiO2-modified polyvinyl alcohol composite (H-SiO2-G-PVA) sponge with extraordinary rigid structure after oil adsorption is designed for durable oil remediation. Through a two-step hydrolysis-condensation process including deposition of silica microparticles and introduction of hexadecyltrimethoxysilane (HDTMS), a superhydrophobic H-SiO2-G-PVA sponge has been successfully constructed. The sponge presents stable superhydrophobicity in various complex environments，therefore it efficiently adsorbs oil from water (up to 6 g g-1) and separate surfactant-stabilized water/oil emulsion with high efficiency (>99%). Noticeably, the H-SiO2-G-PVA sponge maintains tough strength (3.5 MPa) after oil adsorption, which ideally overcomes secondary oil spilling problem and endows the sponge with excellent recycling performances (>20 cycles). Meanwhile, the excellent biocompatibility of the sponge (high cell viability of 91.85%) ensures the potential for practical applications. This rigid, eco-friendly oil-adsorbing sponge that achieves stable superhydrophobicity and recyclability, fulfills the application needs for durable oil remediation.

High vulnerability and a big conservation gap: Mapping the vulnerability of coastal scleractinian corals in South China.

Scleractinian corals build the most complex and diverse ecosystems in the ocean with various ecosystem services, yet continue to be degraded by natural and anthropogenic stressors. Despite the rapid decline in scleractinian coral habitats in South China, they are among the least concerning in global coral vulnerability maps. This study developed a rapid assessment approach that combines vulnerability components and species distribution models to map coral vulnerability within a large region based on limited data. The approach contained three aspects including, exposure, habitat suitability, and coral-conservation-based adaptive capacity. The exposure assessment was based on seven indicators, and the habitat suitability was mapped using Maximum Entropy and Random Forest models. Vulnerability of scleractinian corals in South China was spatially evaluated using the approach developed here. The results showed that the average exposure of the study region was 0.62, indicating relatively high pressure. The highest exposure occurred from the east coast of the Leizhou Peninsula to the Pearl River Estuary. Aquaculture and shipping were the most common causes of exposure. Highly suitable habitats for scleractinian corals are concentrated between 18°N-22°N. Only 21.6 % of the potential coral habitats are included in marine protected areas, indicating that there may still be large conservation gaps for scleractinian corals in China. In total, 37.7 % of the potential coral habitats were highly vulnerable, with the highest vulnerability appearing in the Guangdong Province. This study presents the first attempt to map the vulnerability of scleractinian corals along the coast of South China. The proposed approach and findings provide an essential tool and information supporting the sustainable management and conservation of coral reef ecosystems, addressing an important gap on the world's coral reef vulnerability map.

Proteome and microbiota analyses characterizing dynamic coral-algae-microbe tripartite interactions under simulated rapid ocean acidification.

Ocean acidification (OA) is a pressing issue currently and in the future for coral reefs. The importance of maintenance interactions among partners of the holobiont association in the stress response is well appreciated; however, the candidate molecular and microbial mechanisms that underlie holobiont stress resilience or susceptibility remain unclear. Here, to assess the effects of rapid pH change on coral holobionts at both the protein and microbe levels, combined proteomics and microbiota analyses of the scleractinian coral Galaxea fascicularis exposed to three relevant OA scenarios, including current (pHT = 8.15), preindustrial (pHT = 8.45) and future IPCC-2100 scenarios (pHT = 7.85), were conducted. The results demonstrated that pH changes had no significant effect on the physiological calcification rate of G. fascicularis in a 10-day experiment; however, significant differences were recorded in the proteome and 16S profiling. Proteome variance analysis identified some of the core biological pathways in coral holobionts, including coral host infection and immune defence, and maintaining metabolic compatibility involved in energy homeostasis, nutrient cycling, antibiotic activity and carbon budgets of coral-Symbiodiniaceae interactions were key mechanisms in the early OA stress response. Furthermore, microbiota changes indicate substantial microbial community and functional disturbances in response to OA stress, potentially compromising holobiont health and fitness. Our results may help to elucidate many complex mechanisms to describe scleractinian coral holobiont responses to OA and raise interesting questions for future studies.

Nitrogen cycling in a tropical coral reef ecosystem under severe anthropogenic disturbance in summer: Insights from isotopic compositions.

Coral reefs, one of the most productive ecosystems, have been dramatically declining in recent decades. While studies contend a prominent correlation between coral reef degradation and increased anthropogenic nitrogen (N) loads, a quantitative description of the N sources and cycling processes in these ecologically important ecosystems is lacking. Through a comprehensive depiction of the δ15N compositions of seawaters and sediments, we systematically accessed the N cycling processes in the Weizhou coral reef ecosystem. The correlations between the nitrate (NO3-) concentrations and isotopic compositions (δ15N/δ18O-NO3-) indicated the pelagic NO3- loads were largely regulated by mixing between precipitation and sewage. Biological NO3- turnover processes appeared to be weak. In the sediments, N2 fixation contributed about one-third of the sedimentary organic N, with the rest coming from the settlement of pelagic organic N. We also uncovered significant sedimentary mineralization-nitrification-denitrification processes in which the N loss was greater than the input. While pelagic N significantly contributed to the sedimentary N, the N export from the sediments to surface seawater was potentially short-circuited by the high N retention and recycling efficiencies of the organisms in the coral reef ecosystem. Overall, this study shows that the complex N cycling processes in the ecosystem are effectively reflected in the isotopic compositions of seawater and sediment, thus adding an important dimension to understanding the N cycling in coral reef ecosystems.

Untangling ITS2 genotypes of algal symbionts in zooxanthellate corals.

Collectively called zooxanthellae, photosynthetic dinoflagellates in the family Symbiodiniaceae are typical endosymbionts that unequivocally mediate coral responses to environmental changes. Symbiodiniaceae are genetically diverse, encompassing at least nine phylogenetically distinct genera (clades A-I). The ribosomal internal transcribed spacer 2 (ITS2) region is commonly utilized for determining Symbiodiniaceae diversity within clades. However, ITS2 is often inadvertently interpreted together with the tailing part of the ribosomal RNA genes (5.8S and 28S or equivalent), leading to unresolved taxonomy and equivocal annotations. To overcome this hurdle, we mined in GenBank and expert reference databases for ITS2 sequences of Symbiodiniaceae having explicit boundaries with adjacent rRNAs. We profiled a Hidden Markov Model of the ITS2-proximal 5.8S-28S rRNA interaction, which was shown to facilitate the delimitation of Symbiodiniaceae ITS2 from GenBank, while considerably reducing sequence ambiguity and redundancy in reference databases. The delineation of ITS2 sequences unveiled intra-clade sequence diversity and inter-clade secondary structure conservation. We compiled the clean data into a non-redundant database that archives the largest number of Symbiodiniaceae ITS2 sequences known to date with definite genotype/subclade representations and well-defined secondary structures. This database provides a fundamental reference catalog for consistent and precise genotyping of Symbiodiniaceae and a tool for automated annotation of user-supplied sequences.

Recent collections of sea spiders (Arthropoda: Pycnogonida) from China seas, with some new records and a checklist of the area.

Though research about sea spiders limited in China seas, a complete checklist has not yet exist so far. After checking recent collections obtained from Shandong, Zhejiang, Fujian and the East China Sea, all these sixty-eight specimens were identified as six species belonged to four families and five genera, including three ones new to China. We described and illustrated them in this study, and also revised all previous records about Chinese pycnogonids and provided a checklist for the presently known forty-one species.

Temporal changes of a food web structure driven by different primary producers in a subtropical eutrophic lagoon.

Coastal lagoons are often characterized by eutrophic conditions which are known to impair the structure and functioning of both pelagic and benthic compartments. However, the manner in which eutrophication triggers a series of cascade effects in the whole food web in coastal lagoons has received little attention. Using stable isotope (SI) analyses, we investigated the food web structure in the hypertrophic lagoon of Yundang (Xiamen, China) in two periods of the year characterized by the recurrent alternation of Ulva lactuca and phytoplankton blooms in the cool (March) and warm (September) seasons, respectively. Large temporal fluctuations in the dominance of primary producers (i.e. macroalgae vs. phytoplankton) and, thus, in the available food items, were reflected in major changes in the diet and SI signals of several primary consumers, such as the amphipod Grandidierella japonica, the polychaetes Neanthes japonica and Capitella capitata, and omnivorous fishes (i.e. Mugil cephalus, Oreochromis niloticus, and Sardinella zunasi), while these changes were limited in top carnivorous fishes, such as Lateolabrax japonicus. Furthermore, reduced macrozoobenthic abundance available for omnivores in September was found to force omnivores to switch their feeding habits to those of herbivores. The present study provides evidence that the periodical alternation of macroalgal and phytoplankton blooms throughout the year strongly affect the relations among different trophic levels leading to a cascading effect across the whole food web and to major changes in the lagoon's food web structure. Importantly, our study shows that the lagoon's food web structure under persistent eutrophic conditions can still cope with seasonal changes in primary energy source type from macroalgae to microalgae due to the ability of omnivorous fishes to conduit different food sources up to the highest trophic levels. Thus, this study suggests that in such a highly variable eutrophic system, omnivores play a central role in the lagoon's functioning, and help to sustain the biological resources and the ecosystem services provided by the lagoon.

An updated checklist of the marine fish fauna of Redang Islands, Malaysia.

BACKGROUND: Redang Islands Marine Park consists of nine islands in the state of Terengganu, Malaysia. Redang Island is one of the largest off the east coast of Peninsular Malaysia, which is famous for its crystal-clear waters and white sandy beaches. The ichthyofauna of the Redang archipelago was surveyed by underwater visual observations between August 2016 and May 2018. Census data were compiled with existing records into the checklist of the marine fish of the Redang archipelago presented herein. A total of 314 species belonging to 51 families were recorded. The most speciose families (Pomacentridae, Labridae, Scaridae, Serranidae, Apogonidae, Carangidae, Gobiidae, Chaetodontidae, Lutjanidae, Nemipteridae and Siganidae) were also amongst the most speciose at the neighbouring Tioman archipelago (except Chaetodontidae). The coral fish diversity index value for the six families of coral reef fishes (Chaetodontidae, Pomacanthidae, Pomacentridae, Labridae, Scaridae and Acanthuridae) of the study sites was 132. We estimated that there were 427 coral reef fish species in the Redang archipelago. According to the IUCN Red List, eight species are Near Threatened (Carcharhinus melanopterus, Chaetodon trifascialis, Choerodon schoenleinii, Epinephelus fuscoguttatus, E. polyphekadion, Plectropomus leopardus, Taeniura lymma and Triaenodon obesus), eleven are Vulnerable (Bolbometopon muricatum, Chaetodon trifasciatus, Chlorurus sordidus, Dascyllus trimaculatus, Epinephelus fuscoguttatus, E. polyphekadion, Halichoeres marginatus, Heniochus acuminatus, Nebrius ferrugineus, Neopomacentrus cyanomos and Plectropomus areolatus) and three are Endangered (Amphiprion clarkia, Cheilinus undulatus and Scarus ghobban) in the Redang archipelago. NEW INFORMATION: Five species are new records for Malaysia (Ctenogobiops mitodes, Epibulus brevis, Halichoeres erdmanni, H. richmondi and Scarus caudofasciatus) and 25 species are newly recorded in the Redang archipelago.

First record of the dotted grouper Epinephelusepistictus (Temminck & Schlegel, 1843) (Perciformes, Serranidae) in Malaysia.

Five specimens of Epinephelusepistictus (Temminck & Schlegel, 1843) were collected from a major landing site located on the west coast of Peninsula Malaysia during a fish faunal survey on 23 August 2017. The present study extends the distribution range of E.epistictus southwards from Andaman Sea to the Strait of Malacca. Species identification was confirmed by colour pattern and DNA barcoding (567 bp of cytochrome C oxidase I) of all E.epistictus specimens and nine closely related Epinephelus species. The interspecies genetic distance ranged from 0.002-0.245. This study also presents, for the first time for Malaysia, data on length-weight relationships and otolith measurements. It contributes to a better understanding of taxonomy, and phylogenetic and genetic diversity of E.epistictus.

Spatiotemporal variation in environmental features and elemental/isotopic composition of organic matter sources and primary producers in the Yundang Lagoon (Xiamen, China).

Aquatic eutrophication is a major problem globally, leading to significant chemical-compositional changes in the first trophic levels of a food web. These will consequently affect the whole food web dynamics in eutrophic coastal ecosystems. In this study, we analyzed the spatiotemporal variation in water chlorophyll-a, total organic carbon (TOC) and TOC/Chl-a ratio, and in the elemental/isotopic (Cat/Nat, δ13C, δ15N) composition of particulate organic matter (POM), phytoplankton, sedimentary organic matter, benthic microalgae, U. lactuca, and decaying leaves of mangrove plants in the eutrophic, urban lagoon of Yundang (Xiamen, China). Investigations were carried out in four different sectors of the lagoon in March (dominated by Ulva lactuca) and September (dominated by phytoplankton) 2009, and the feasible contribution of potential organic matter (OM) sources to POM was assessed in each period. The results showed significant spatiotemporal variation in δ13C and δ15N of POM, owing to changes in its carbon sources. The POM in the diversion canal (POMDC) of the lagoon originated mainly from terrestrial OM both in March and September, as evidenced by a Cat/Nat ratio of 12~17 and a TOC/Chl-a ratio exceeding 400, as well as depleted δ13C (- 27.3~- 23.7‰) and δ15N (- 2.8~0.1‰). The POM in the main canal (POMMC) and the inner (POMIL) and outer (POMOL) sectors of the lagoon were largely composed of lagoon-borne phytoplankton in September. This was revealed by TOC/Chl-a values below 100 and enriched δ13C values (- 22.7~- 17.9‰) which are close to the values typical for fresh phytoplankton. However, these were strongly regulated by exogenous OM in March. The combined contribution of POMMC and POMDC to POM in March reached 64-99% in the inner lagoon and 67-88% in the outer lagoon. Non-living POM, which originates from terrestrial organic detritus, was the main contributor to POM (60.7~85.7%) both in the inner and outer sections of the lagoon. Overall, the present study demonstrates that the temporal changes in the dominance of primary producers were reflected in significant variation in the environmental features and elemental/isotopic composition of OM sources and their contribution to POM in the Yundang Lagoon. To further our understanding of the effects of eutrophication due to different primary producers on the resource partitioning in the Yundang Lagoon, additional studies on the consumers and the whole food web of the lagoon are expected.

Different calcification responses of two hermatypic corals to CO2-driven ocean acidification.

Understanding how calcification is influenced by the enhanced dissolution of CO2 in the oceans is the key to evaluating the effects of ocean acidification (OA) on coral reefs. In this study, two branching hermatypic corals widely distributed in the South China Sea, Pocillopora damicornis and Seriatopora caliendrum, were used to study the calcification responses to CO2-driven OA (7.77 ± 0.07 vs. 8.15 ± 0.12). Our results showed that the calcification rate (0.17 ± 0.04%/day to 0.21 ± 0.12%/day) in P. damicornis remained unchanged in the acidified seawaters, but that in S. caliendrum decreased significantly (0.62 ± 0.21%/day to 0.44 ± 0.11%/day). Our results suggested that reef corals with high calcification rates may be more susceptible to the enhanced dissolution of CO2. Differential calcified response to elevated CO2 may be closely attributed to coralline capacity of the upregulation at their site of calcification in acidified seawater.