Introduction: Shellfish play an important role in ecological restoration and as carbon (C) sinks, but studies on their ecological carrying capacity (ECC) and C sequestration potential are sparse.Methods: In this study, we selected a 57-hectare artificial oyster reef in a typical marine ranching in Bohai Bay, China, to evaluate the ECC and their C sequestration potential of bivalve shellfish, and projecting their impact on functional groups in the system, with an Ecopath with Ecosim (EwE) food web model. We conducted four biological surveys to obtain the biomass measurements, with one conducted in each of the summer, autumn, and winter of 2019 and one in the spring of 2020; and the functional groups included in the surveys comprised fish, cephalopods, crustaceans, snails, bivalve shellfish, annelids, other macrobenthos, meiobenthos, starfish, sea cucumbers, zooplankton, phytoplankton, and detritus.Results and Discussion: The EwE model prediction results showed that the ECC of bivalve shellfish was established to be 282.66 t/km², far more than the existing quantity of 187.76 t/km². Therefore, at present, the ecosystem of the study marine ranching is not yet mature. Moreover, our ecological network analysis parameters indicated that the marine ranching ecosystem will be mature and stable when the bivalve shellfish population reaches its ECC. However, the increase in bivalve shellfish biomass will result in a decrease in the population sizes of species competing for food resources with bivalve shellfish, mainly gobiid fish such as Tridentiger bifasciatus, Tridentiger trigonocephalus, Tridentiger barbatus. Simultaneously, when the bivalve shellfish reach their ECC, 29.23 t of CO₂ can be sequestrated by bivalve shellfish, comprising 14.32 t being removed from the ecosystem as prey and 14.91 t being stored on the seafloor through biodeposition.Conclusion: Therefore, the research demonstrated that, within the scope of ECC, the increasing bivalve shellfish can improve the C sequestration capacity of the marine ranch ecosystem, and effective management of bivalve shellfish in marine ranching can improve the economic benefits and C sink service functions of marine ranching.

Objective: This study aimed to study the spatial and temporal variation in archaeal-bacterial community and niche differentiation of nitrite/nitrate-dependent anaerobic methane oxidation (N-/Nr-DAMO) microbes in the sediment of aquaculture ponds. Methods: Field sampling was carried out in May, July and September which represented different farming seasons in Northern China. The sediment samples were collected in the depth range of 0-15 cm at 5 cm intervals. The spatiotemporal distributions of sediment bacteria, archaea and N-/Nr-DAMO microbes, and characterized the niche differentiation of microbes were investigated in grass carp ( Ctenopharyngodon idella ) aquaculture ponds compared with a natural successional pond without human-induced practices. The copy numbers of total bacteria, total archaea, N-DAMO bacterial pmoA and Nr-DAMO archaeal mcrA were determined by qPCR, and the microbial community composition were determined by high-throughout sequencing analysis. Results: Bacterial and archaeal abundances and diversities were significantly higher in aquaculture ponds than in natural succession ponds, with distinct vertical distribution patterns. Specifically, the bacterial abundance and diverse, as well as the archaeal abundance showed decreasing trends with increasing sediment depth, whereas diversities of archaea displayed an opposite trend that increased with sediment depth in May and July. Bacterial co-occurrence networks were less complex in aquaculture ponds. In the case of N-DAMO bacteria, the copy numbers of the functional gene pmoA , the relative abundance, and diversity were higher, while their occurrences in bacterial networks were lower. The archaeal co-occurrence networks were more complexity and stability in aquaculture pond sediment. In the case of Nr-DAMO archaea, their relative abundances decreased significantly, and fewer Nr-DAMO archaea were present in the archaeal co-occurrence networks. Conclusion: The vertical profiles, as well as the aquaculture practices impact the bacterial and archaeal community structure which were shaped mostly by ORP and nutrient availability. In aquaculture ponds, bacterial co-occurrence networks were less complex, and fewer N-DAMO bacteria were presented in the bacterial co-occurrence networks. The archaea (e.g. desulphurizor, denitrifiers, methanogens) showed negatively correlated with respect to the distribution of Nr-DAMO archaea which were fewer presented in the archaeal co-occurrence networks. These results appeared that the niches of N-/Nr-DAMO microbes were suppressed in aquaculture ponds.

Baiyangdian Lake, the largest freshwater shallow lake on the North China Plain, plays a pivotal role in maintaining the regional ecological balance and biodiversity. Meiofauna are integral components of Baiyangdian Lake; however, their community characteristics and relationship with environmental factors have not yet been studied. The aim of the following study was to evaluate the density, spatiotemporal patterns, and habitat response dynamics of meiofauna in Baiyangdian Lake. A field investigation was conducted at 33 sites spanning various habitats, including aquatic plant-dominant, trench, and pelagic areas, across the spring, summer, and autumn seasons of 2021. The results revealed that the meiofauna in Baiyangdian Lake primarily comprise freshwater nematodes (91.78%), ostracods, and copepods, with a mean abundance of 69.40 ± 35.20 ind. 10 cm⁻², peaking in the spring, followed by summer and autumn. The mean biomass was 164.95 ± 99.39 dwt. 10 cm⁻², with that of ostracods being the most substantial and that of copepods being the least, with both of them exhibiting seasonal fluctuations. Notably, in the summer, the abundance of meiofauna was positively correlated with the water depth and negatively correlated with ammonia nitrogen levels (R² = 0.13 and R² = 0.24, respectively; p < 0.05 and p < 0.01; n = 33). The results of our study indicate that the distribution and abundance of meiofauna are significantly affected by environmental factors, with the water depth and ammonia nitrogen levels being potential key determinants. The results of the present study are conducive to evaluating the health status of the Baiyangdian ecosystem, protecting biodiversity, and studying the impacts of anthropogenic activities and environmental changes on the lake, and can also provide scientific support for its ecological restoration and governance as well as the assessment of ecological service functions.