The super typhoon Lekima (2019) resulted in massive losses in large seagrass (Zostera japonica) meadows, soil organic carbon and nitrogen pools in the intertidal Yellow River Delta, China

Nonuniform organic carbon stock loss in soils across disturbed blue carbon ecosystems

Conserving blue carbon ecosystems (BCEs) has gained international attention in climate change mitigation, reflected in United Nations policies and voluntary carbon-offset projects. These efforts assume significant and uniform losses of soil organic carbon (Corg) throughout the top meter following disturbances, yet this assumption lacks robust empirical support. Here, we synthesized 239 paired observations of intact and disturbed BCEs globally. Soil Corg stock losses in the top meters vary widely: from -68.4% (agricultural conversion, ±13.4%, 95% confidence interval) to +0.8% (harvesting, ±46.2%) in mangroves, -25.9% (climate/hydrological change, ± 30.7%) to +48.6% (grazing, ±78.7%) in saltmarshes, and -34.2% (vegetation cover damage, ±22.4%) to -27.4% (dredging, ±33.6%) in seagrasses. Extensive disturbances deplete Corg down to 50-200 cm, while limited disturbances impact only the top 10-30 cm or resulted in negligible losses. This refinement contributes to improved global inventories of greenhouse gas emissions from BCEs, supporting abatement policy settings for nationally determined contributions commitments.

Climate change challenges coastal blue carbon restoration in China

Coastal blue carbon has become an emerging natural climate solution (NCS) that offers significant potential for mitigating global climate change while providing various ecosystem services. However, blue carbon ecosystems, including mangroves, tidal salt marshes, and seagrass meadows, are susceptible to the impacts of climate change, which in turn affects their potential to mitigate climate change. In this study, we employed the MaxEnt to evaluate the potential suitable areas and carbon sink potential of China's Coastal blue carbon ecosystem under three climate scenarios for the present and projected conditio ns in 2050. Our results reveal that China's coastal blue carbon ecosystems have an estimated carbon sequestration potential of 8.65 ∗ 105 t/a. Specifically the potential annual carbon sequestration of mangroves is 1.457 ∗ 105 t/a, tidal salt marshes is 6.714 ∗ 105 t/a, and seagrass is 4.769 ∗ 104 t/a. By 2050, due to climate change, the annual carbon sequestration potential of China's coastal blue carbon is projected to decrease by 0.733-2.351 ∗ 105 t/a, representing an 8-27 % reduction from the current levels. Furthermore, the distribution of potential suitable areas for these blue carbon ecosystems is expected to shifted to different degrees, among which the potential suitable areas of mangrove will be transferred to the greatest extent, showing a trend of northward expansion. Future conservation and restoration efforts for blue carbon ecosystems ought to consider the impact of climate change and fully utilize the potential of blue carbon.

The largest single-species Nanozostera japonica seagrass meadow of China: Its decline, restoration attempts, and short-term effects on macrobenthos and soil bacterial communities

Seagrass beds support vital ecological functions so that when seagrass experience severe degradation, their ecosystem service functions are diminished or lost. The largest Nanozostera japonica seagrass bed in China, situated in the Yellow River Delta, has undergone significant degradation due to Spartina alterniflora invasion and the impact of Typhoon Lekima (2019). The lack of seeds and overwintering shoots makes natural seagrass recovery challenging, prompting the urgent need for seagrass ecological restoration. In the present study, seed sowing experiments were conducted with varying burial depths, seed sources, and sowing times, as well as transplantation experiments with different transplant unit sizes and intervals in the severely degraded seagrass bed. Subsequently, changes in macrobenthos and soil bacterial diversity were tracked after seagrass recovery. According to the results, the optimal burial depth for N. japonica seeds varies across different sediment types, with 4 cm being suitable for sandy soil and 2 cm for silty soil. Seeds sown in May did not survive due to high temperatures. Seeds from Dalian exhibited superior growth after sowing, making them ideal material for seed restoration projects. Transplanting N. japonica sods with 25 × 25 cm transplant units and 50-cm intervals resulted in the most robust growth, indicating it as a suitable method for adult transplantation. Following seagrass re-establishment, macrobenthos and soil bacterial diversity increased significantly. The findings of the present study provide valuable technical guidance and theoretical support for the ecological restoration of N. japonica. Future efforts should prioritize the restoration of seagrass bed ecological functions, with longer-term effects examined.

Spatial variability in blue carbon storage and sequestration of seagrass meadows in southern China

Although seagrass meadows are intense carbon sinks, information on the regional variability in seagrass blue carbon stocks and carbon sequestration remains limited. We estimated the organic carbon (Corg) stocks and carbon accumulation rates (CAR) of seven seagrass meadows along the subtropical coast of China's Zhanjiang City and analyzed the driving factors of variability in sediment Corg stocks in three seagrass meadows. Results showed that most Corg (99.83 %) was stored in the sediments, and the contribution of living biomass was minor. The average Corg stocks of living biomass and sediments across all sites were 0.04 ± 0.01 and 42.03 ± 25.07 Mg C ha-1, respectively, which were significantly lower than the world average (2.52 ± 0.48 and 194.2 Mg C ha-1). The sediment Corg stocks of the upper 1 m ranged from 24.26 to 157.12 Mg C ha-1 with substantial variability among sites: Liusha Bay (64.93 ± 22.31 Mg C ha-1) > Donghai Island (33.8 ± 10.65 Mg C ha-1) > Dongshen Ferry (27.35 ± 4.15 Mg C ha-1). The average sediment CAR was 53.47 g C m-2 yr-1, and the total CAR of 864.18 ha seagrass meadows was 260.76 ± 4.86 Mg C yr-1 in these studied sites. Physicochemical factors, such as high moisture content, salinity, CaCO3 content, and low dry bulk density, jointly inhibited the mineralization rate of Corg in sediments. Our study provides data from understudied regions to a growing dataset on seagrass carbon stocks and sequestration rates and highlights the significance of local and regional differences in seagrass blue carbon storage to accurately assess the climate change mitigation potential of seagrass ecosystems.

Population genetic patterns across the native and invasive range of a widely distributed seagrass: Phylogeographic structure, invasive history and conservation implications

Aim

The seagrass Zostera japonica is a dramatically declined endemic species in the Northwestern Pacific from the (sub)tropical to temperate areas, however, it is also an introduced species along the Pacific coast of North America from British Columbia to northern California. Understanding the population's genetic patterns can inform the conservation and management of this species.

Location

North Pacific.

Methods

We used sequences of the nuclear rDNA internal transcribed spacer (ITS) and chloroplast trnK intron maturase (matK), and 24 microsatellite loci to survey 34 native and nonnative populations (>1000 individuals) of Z. japonica throughout the entire biogeographic range. We analysed the phylogeographic relationship, population genetic structure and genetic diversity of all populations and inferred possible origins and invasion pathways of the nonnative ones.

Results

All markers revealed a surprising and significant deep divergence between northern and southern populations of Z. japonica in the native region separated by a well-established biogeographical boundary. A secondary contact zone was found along the coasts of South Korea and Japan. Nonnative populations were found to originate from the central Pacific coast of Japan with multiple introductions from at least two different source populations, and secondary spread was likely aided by waterfowl.

Main Conclusions

The divergence of the two distinct clades was likely due to the combined effects of historical isolation, adaptation to distinct environments and a contemporary physical barrier created by the Yangtze River, and the warm northward Kuroshio Current led to secondary contact after glacial separation. Existing exchanges among the nonnative populations indicate the potential for persistence and further expansion. This study not only helps to understand the underlying evolutionary potential of a widespread seagrass species following global climate change but also provides valuable insights for conservation and restoration.

Tropical cyclone impacts on seagrass-associated fishes in a temperate-subtropical estuary

Major storms can alter coastal ecosystems in several direct and indirect ways including habitat destruction, stormwater-related water quality degradation, and organism mortality. From 2010–2020, ten tropical cyclones impacted coastal North Carolina, providing an opportunity to explore ecosystem responses across multiple storms. Using monthly trawl and contemporaneous seagrass surveys conducted in Back Sound, NC, we evaluated how cyclones may affect the nursery role of shallow-water biogenic habitats by examining seagrass-associated fish responses within a temperate-subtropical estuary. We employed a general before-after-control-impact approach using trawls conducted prior (before) and subsequent (after) to storm arrival and years either without (control) or with (impact) storms. We examined whether effects were apparent over short (within ~three weeks of impact) and seasonal (May-October) timescales, as well as if the magnitude of storm-related shifts varied as a function of storm intensity. Our findings suggest that the ability of these shallow-water habitats to support juvenile fishes was not dramatically altered by hurricanes. The resilience exhibited by fishes was likely underpinned by the relative persistence of the seagrass habitat, which appeared principally undamaged by storms based upon review of available–albeit limited seagrass surveys. Increasing cyclone intensity, however, was correlated with greater declines in catch and may potentially underlie the emigration and return rate of fish after cyclones. Whether estuarine fishes will continue to be resilient to acute storm impacts despite chronic environmental degradation and predicted increases major tropical cyclone frequency and intensity remains a pressing question.