Integrative taxonomy reveals the biodiversity of intertidal marine flatworms of the suborder Acotylea (Platyhelminthes: Polycladida) in the South China Sea

Parabens and their metabolite in a marine benthic-dominated food web from the Beibu gulf, South China Sea: Occurrence, trophic transfer and health risk assessment

Pseudo‐nitzschia is a group of widely distributed planktonic diatoms. Some species produce the neurotoxin domoic acid. Herein, two new Pseudo‐nitzschia species were described from Chinese coastal waters and the South China Sea after combining morphological and molecular data, together with biogeographical traits. Pseudo‐nitzschia punctionis sp. nov. was similar to Pseudo‐nitzschia bipertita morphologically, but differed in poroid structure, which was undivided in P. punctionis but divided in two sectors in P. bipertita. This difference corresponded to the presence of two hemicompensatory base changes (HCBCs) in the secondary structure of internal transcribed spacer 2. Pseudo‐nitzschia polymorpha sp. nov. was sister to Pseudo‐nitzschia limii phylogenetically, but distinct by the various shapes of perforations on the valve and copula, which was supported by four HCBCs. In a metabarcoding analysis, multiple new ribotypes were identified within the two new species, and intraspecific genetic divergences were analyzed. Metabarcoding data revealed that P. punctionis had a broader temperature range (12.9–30.5°C) than P. polymorpha (22.3–30.5°C). Within the two new species, different traits were found among the amplicon sequence variants regarding temperature and biogeography, representing different microevolutionary directions under environmental selection. The two new species had different biogeographical traits when compared to their closely related species. Domoic acid was detected in strains of P. punctionis at a concentration of 13.5–17.7 fg/cell, but the toxin was not found in strains of P. polymorpha. A combination of characters based on laboratory strains and field metabarcoding data provided more data for delimiting Pseudo‐nitzschia species and gave new insights into their diversity and biogeography.

Ecotoxicology of Methylmercury: A Transdisciplinary Challenge

Pollution and health risks of antibiotics in marine food webs from the South China Sea.

The finless porpoise (Neophocaena phocaenoides) inhabits a wide range of tropical and temperate waters of the Indo-Pacific region. Genetic structure of finless porpoises in Chinese waters in three regions (Yangtze River, Yellow Sea, and South China Sea) was analyzed, including the Yangtze finless porpoise which is widely known because of its highly endangered status and unusual adaptation to freshwater. To assist in conservation and management of this species, ten microsatellite loci were used to genotype 125 individuals from the three regions. Contrary to the low genetic diversity revealed in previous mtDNA control region sequence analyses, relatively high levels of genetic variation in microsatellite profiles (H E = 0.732–0.795) were found. Bayesian clustering analysis suggested that finless porpoises in Chinese waters could be described as three distinct genetic groups, which corresponded well to population “units” (populations, subspecies, or species) delimited in earlier studies, based on morphological variation, distribution, and genetic analyses. Genetic differentiation between regions was significant, with F ST values ranging from 0.07 to 0.137. Immigration rates estimated using a Bayesian method and population ancestry analyses suggested no or very limited gene flow among regional types, even in the area of overlap between types. These results strongly support the classification of porpoises in these regions into distinct evolutionarily significant units, including at least two separate species, and therefore they should be treated as different management units in the design and implementation of conservation programmes.

Comparison of potentially toxic elements (PTEs) in marine and freshwater food webs: Levels, bioaccumulation, and trophodynamics.

The widespread presence of plastic debris in marine ecosystems was first highlighted as a serious concern in the United Nations Convention on the Law of the Sea (UNCLOS) and the 1972 London Convention. This realization identified plastic pollution as one of the major global environmental issues. Majorities of plastic debris are neither recycled nor incinerated, as a result, it eventually makes its way into lakes, rivers, and oceans. Analysis of water and sediment worldwide indicates that microplastics and nanoplastic are ubiquitous in soils, freshwater, and marine ecosystems. Microplastic and nanoplastics are distributed throughout marine environments via processes such as biofouling and chemical leaching, contaminating both pelagic and benthic species. Despite growing recognition of the hazards posed by microplastics and nanoplastics, regulatory efforts remain hampered by limited understanding of their broader ecological impacts, particularly how diverse factors translate into population declines and ecosystem disruptions. This review examines the pathways of microplastic and nanoplastic pollution, their interactions with other environmental stressors such as climate change and chemical pollution, and their effects on marine food webs. The review highlights the urgent need for further research into the behavior and fate of nanoplastics, which are the degradation product of microplastics, owing to their nano size they pose additional risks, unique properties, and potential for widespread ecological impacts. Studies have demonstrated that smaller microplastics and nanoplastics, particularly nanoplastics, are more toxic than larger microplastics. Additionally, microplastics and nanoplastics serve as vectors for contaminants such as heavy metals, exacerbating their toxicity. They also translocate through marine food chains, posing potential health risks. While evidence of their impact continues to grow, the chronic toxicity of microplastics and nanoplastics remains poorly understood, emphasizing the need for further research, particularly at the cellular level, to fully understand their effects on marine ecosystems and human health. This review also concludes with a call for standardized measurement methods, effective mitigation strategies, and enhanced international cooperation to combat this escalating threat. Future research should prioritize the complex interactions between microplastics and nanoplastics, other pollutants, and marine ecosystems, with the ultimate goal of developing holistic approaches to manage and mitigate the impact of plastic pollution. PRACTITIONER POINTS: Microplastic/nanoplastic translocate through marine food webs, affecting species and human health. Nanoplastics are more toxic than microplastics, exacerbating environmental risks. Nanoplastic aggregation influences their distribution and ecological interactions. Future research should focus on nanoplastic behavior, transport, and toxicity.

Gastropod pedal mucus retains microplastics and promotes the uptake of particles by marine periwinkles

ABSTRACTAimCopepods are the key secondary producers in marine ecosystems, yet their in situ diet and symbionts remain underexplored due to technical challenges, limiting our understanding of their population dynamics and ecological functions. Using DNA metabarcoding, we jointly characterised the natural diet and symbionts of copepods across Chinese coastal waters, aiming to unveil their diversity, dynamics, and ecological drivers under various environmental conditions.LocationThree coastal regions of Chinese seas: Qinhuangdao coastal waters (the Bohai Sea), the South Yellow Sea, the Yangtze River estuary and its adjacent waters.MethodsCopepods were sorted and pooled by species for DNA extraction. The 18S rDNA of diet (gut content) and symbiont were amplified using modified copepod‐excluding eukaryote‐common primers and subjected to high‐throughput sequencing. Analyses covered OTU‐based diversity, feeding selectivity, host preference, and environmental drivers. Co‐occurrence network analysis characterised the potential association between prey and symbionts. Symbiotic ciliate genetic diversity was assessed via phylogenetic reconstruction.ResultsOur protocol effectively suppressed amplification from 13 copepod species while capturing all eukaryotic supergroups spanning over 30 phyla. Diverse diet and symbionts are associated with copepods, including taxa unreported in copepods or Chinese waters. Environmental filtering, rather than copepod identity, primarily shaped diet and symbiont communities, and prey‐symbiont associations also contributed. Copepods exhibited significant trophic plasticity, evidenced by wide feeding selectivity ratios across samples. Nine symbiotic ciliate ribogroups were revealed and unevenly distributed among hosts and regions, suggesting host specificity or environmental preference.Main ConclusionsOur findings demonstrate the feasibility of DNA metabarcoding for profiling copepod natural diet and symbionts. We unveiled their higher diversity and dynamic variability than previously recognised, positioning copepods as amplifiers of hidden marine microbial diversity. Protecting the intricate trophic and symbiotic network associated with copepods is critical for future marine ecosystem conservation.

Bioaccumulation and potential risk of organophosphate flame retardants in coral reef fish from the Nansha Islands, South China Sea

Reappraising adaptive radiation

Perfluoroalkyl substances in marine food webs from South China Sea: Trophic transfer and human exposure implication

The increasing discharge and ubiquitous occurrence of novel brominated flame retardants (NBFRs) in aquatic environments have initiated intense global concerns; however, little information is available regarding their structure-related trophodynamics in marine food webs. In this study, a tropical marine food web including 29 species (18 fish and 11 invertebrate species) was collected from coral reef waters of the Xisha Islands, the South China Sea, for an analysis of 11 representative NBFRs. The mean ∑NBFR concentrations generally increased in the following sequence: sea cucumbers (0.330 ng/g lw) < crabs (0.380 ng/g lw) < shells (2.10 ng/g lw) < herbivorous fishes (2.30 ng/g lw) < carnivorous fishes (4.13 ng/g lw), with decabromodiphenyl ethane (DBDPE) and hexabromobenzene (HBB) as the predominant components. Trophic magnification was observed for all of the investigated NBFRs, with trophic magnification factors (TMFs) ranging from 1.53 (tetrabromobisphenol A bis(dibromopropyl ether)) to 5.32 (HBB). Significant negative correlations were also found between the TMFs and the tested in vitro transformation clearance rates (CLinvitro) for the target NBFRs except for bis(2-ethylhexyl)-3,4,5,6-tetrabromo-phthalate (TBPH) (p < 0.05). Multiple linear regression analysis confirmed that the transformation rate is a more powerful predictor for TMFs than the hydrophobicity of NBFRs in this marine food web.

the recovery of fishery resources and sustainability of the marine ecosystem functions. However, how these stressors interactively impact the ecosystems is still poorly understood. Thus, disentangling the effect of these stressors on marine fisheries and ecosystem dynamics will help us better understand the synergies and dependencies of fishery resources, diversity, nutrient cycles, ecosystem threats, and management practices. More importantly, it will provide managers and decision-makers with reliable information for management to preserve marine biodiversity and recover fishery resources.In this special issue, we collected seventeen research papers linked to this topic about marine fisheries and ecosystems. These papers covered multiple marine biomes, including fishes, zooplankton, and invertebrates, and used various algorithms to analyze the collected data, such as stable isotope, mass models, DNA-based analyses, etc. For instance, an investigation study conducted by Xu et al (2022) identified the species diversity and distribution of crustacean larvae in the Zhongsha Islands waters, South China Sea by using DNA barcoding and molecular species identification approach, revealing that the crustacean diversity in the islands had been seriously underestimated before.Fisheries management policies have received considerable critical attention for their conservation effects on resource recoveries. Compared the carbon transfer efficiency of the three large marine ecosystems around China to other ecosystems, Chen et al (2022) revealed that without proper fisheries management, the fisheries in the ecosystems were likely to collapse with an increasing carbon transfer efficiency. Indeed, effective fisheries management considering other relevant factors that may affect marine ecosystems is imminent and worth exploring. Based on two mass balance models, Xu et al ( 2022) revealed that the implementation of fisheries management policies, especially seasonal fishing moratorium, had positive effects on fishery resources recovery, especially commercial fish in the East China Sea. Thus, they suggested that fishery management in the East China Sea needs to be strengthened by extending the seasonal fishing moratorium and reducing fishing pressure afterward.Climate change is another factor significantly altering marine fisheries and ecosystems over the world. Here, three studies were conducted to explore the role of climate change in affecting specific marine fishery species. Hou et al ( 2022 Moreover, investigating the trophic niches of particularly important commercial fish is also critical to the conservation and management of fishery resources. Stable isotope analysis has been widely used in the past decades in the field. In this topic, Wang et al (2022) and Jiang et al (2022) applied the stable isotope analysis to disentangle the trophic interactions of key fisheries species (Sciaenidae and Thunnus) in the Solomon Islands and Zhoushan Islands, respectively. They both found that niche overlap existed to some extent between the focal species reflecting the similarity of resources used and prey competition between them.Nonetheless, the differentiation in habitats, migration routes, or body size allows their coexistence in an ecosystem in the same area.Nearshore species, estuaries, and bay ecosystems are more vulnerable to human disturbance than other marine species and ecosystems. Zeng et al ( 2022) investigated the impacts of human disturbances on the species and functional dynamics of the demersal fish community in the Pearl River Estuary, highlighting the complicated interactions between the demersal fish community and disturbances. Ke et al (2022) revealed that high anthropogenic nutrient loading might reduce the difference in trophic niches among zooplankton groups. They provided detailed information on the distribution of zooplankton δ13C and δ15N in Jiaozhou Bay, China, which will be useful for understanding the anthropogenic influence on the ecosystem structure and function. Du et al ( 2022) also found that long-term changes existed in zooplankton composition in the Changjiang estuary due to human disturbance and water temperature rise.Besides focusing on the taxonomic species groups, two studies assessed the functioning of marine ecosystems with artificial reefs using Ecopath models. Wang et al ( 2022) provided a dynamic model framework to alternatively estimate the ecological carrying capacity for stock enhancement practices in the development of marine ranching ecosystems. In contrast, Zhang et al (2022) revealed that the current artificial system had formed complicated interspecies relations and high-level stability, which could be a way to alleviate the current natural coral reef crisis. These two studies used a similar approach to illustrate the functioning evolvement of established artificial reefs and provide the scientific basis for the improvement of marine fishery production and management.

The China Seas include the South China Sea, East China Sea, Yellow Sea, and Bohai Sea. Located off the Northwestern Pacific margin, covering 4700000 km2 from tropical to northern temperate zones, and including a variety of continental margins/basins and depths, the China Seas provide typical cases for carbon budget studies. The South China Sea being a deep basin and part of the Western Pacific Warm Pool is characterized by oceanic features; the East China Sea with a wide continental shelf, enormous terrestrial discharges and open margins to the West Pacific, is featured by strong cross-shelf materials transport; the Yellow Sea is featured by the confluence of cold and warm waters; and the Bohai Sea is a shallow semi-closed gulf with strong impacts of human activities. Three large rivers, the Yangtze River, Yellow River, and Pearl River, flow into the East China Sea, the Bohai Sea, and the South China Sea, respectively. The Kuroshio Current at the outer margin of the Chinese continental shelf is one of the two major western boundary currents of the world oceans and its strength and position directly affect the regional climate of China. These characteristics make the China Seas a typical case of marginal seas to study carbon storage and fluxes. This paper systematically analyzes the literature data on the carbon pools and fluxes of the Bohai Sea, Yellow Sea, East China Sea, and South China Sea, including different interfaces (land-sea, sea-air, sediment-water, and marginal sea-open ocean) and different ecosystems (mangroves, wetland, seagrass beds, macroalgae mariculture, coral reefs, euphotic zones, and water column). Among the four seas, the Bohai Sea and South China Sea are acting as CO2 sources, releasing about 0.22 and 13.86– 33.60 Tg C yr−1 into the atmosphere, respectively, whereas the Yellow Sea and East China Sea are acting as carbon sinks, absorbing about 1.15 and 6.92 –23.30 Tg C yr−1 of atmospheric CO2, respectively. Overall, if only the CO2 exchange at the sea-air interface is considered, the Chinese marginal seas appear to be a source of atmospheric CO2, with a net release of 6.01 –9.33 Tg C yr−1 , mainly from the inputs of rivers and adjacent oceans. The riverine dissolved inorganic carbon(DIC) input into the Bohai Sea and Yellow Sea, East China Sea, and South China Sea are 5.04, 14.60, and 40.14 Tg C yr−1 , respectively. The DIC input from adjacent oceans is as high as 144.81 Tg C yr−1 , significantly exceeding the carbon released from the seas to the atmosphere. In terms of output, the depositional fluxes of organic carbon in the Bohai Sea, Yellow Sea, East China Sea, and South China Sea are 2.00, 3.60, 7.40, and 5.92 Tg C yr−1 , respectively. The fluxes of organic carbon from the East China Sea and South China Sea to the adjacent oceans are 15.25–36.70 and 43.93 Tg C yr−1 , respectively. The annual carbon storage of mangroves, wetlands, and seagrass in Chinese coastal waters is 0.36 –1.75 Tg C yr−1 , with a dissolved organic carbon (DOC) output from seagrass beds of up to 0.59 Tg C yr−1 . Removable organic carbon flux by Chinese macroalgae mariculture account for 0.68 Tg C yr−1 and the associated POC depositional and DOC releasing fluxes are 0.14 and 0.82 Tg C yr−1 , respectively. Thus, in total, the annual output of organic carbon, which is mainly DOC, in the China Seas is 81.72 –104.56 Tg C yr−1 . The DOC efflux from the East China Sea to the adjacent oceans is 15.00 –35.00 Tg C yr−1 . The DOC efflux from the South China Sea is 31.39 Tg C yr−1 . Although the marginal China Seas seem to be a source of atmospheric CO2 based on the CO2 flux at the sea-air interface, the combined effects of the riverine input in the area, oceanic input, depositional export, and microbial carbon pump (DOC conversion and output) indicate that the China Seas represent an important carbon storage area.