Mollusc aquaculture homogenizes intertidal soft‐sediment communities along the 18,400 km long coastline of China

Integrated microRNA study and pathological analysis provides new insights into the immune response of Ruditapes philippinarum under Vibrio anguillarum challenge

Manila clam (Ruditapes philippenarum) is an important shellfish aquaculture product. The large-scale breeding of clams is often affected by V. anguillarum and causes large-scale death. However, the pathogenesis, immune response and metabolic pathway of V. anguillarum are still unclear. In this study, we found that the bacterial load in the hepatopancreas of R. philippinarum peaked at 48 h after V. anguillarum infection, and then gradually decreased, while the activity of lysozyme reached the peak at 12 h. Tissue section observation reveals that the infected hepatopancreas cells lost normal structure or necrosis. Additionally, six small RNA libraries were constructed using hepatopancreas of clams. A total of 15 differentially expressed (DE) microRNA (miRNA) were identified at 48 h after V. anguillarum infection, including 8 upregulated and 7 downregulated miRNAs. GO and KEGG enrichment results indicated the prediction of 48 known miRNAs and 127 new miRNAs, with functional annotation suggests that endocytosis pathway and bacterial recognition proteins may play key roles in immune response. The sequencing results were basically consistent with the qRT-PCR validation, indicating the accuracy of the data. This study provides a new idea to explore the immune regulation mechanism of shellfish after V. anguillarum infection, which brings important reference significance for modern immunological research.

Spatiotemporal variations in migratory bird diversity and abundance along the coast of Gochang getbol

Tidal flats provide critical habitat for migratory waterbird species; however, populations of migratory waterbirds have significantly declined due to tidal flat loss and degradation caused by human activities, particularly in Asia. Gochang getbol is one of tidal flats located on the southwest coast of South Korea and a center of clam production. Using bird monitoring data collected at five zones (zone1 to zone5) established across Gochang getbol and near coastal area, we examined distribution patterns of migratory bird diversity and conservation-related species along the coast of Gochang getbol. The intensity of human activity ‒ mudflat culture (mostly bivalve) and aquaculture was relatively high at zone2 and zone3, occupying > 30% of 2km circular area surrounding most sample points of these zones. Zone1 and particularly zone4 contained more natural/semi-natural habitats (less disturbed mudflats and wetlands) and zone5 had smallest mudflat than others. Shannon diversity, species richness, and abundance of migratory birds differed between zones (Anova test, P ≤ 0.02) except Shannon diversity in winter. In fall, all values were higher at zone4 than zone3 and zone5. In winter, zone1 showed greatest species richness and higher abundance than zone2, zone3, and zone5. In spring, while most differences were found between zone4 and zone5, abundance at zone4 was somewhat higher than zone2. The results from the fourth corner analysis indicated that abundance of species foraging at mudflat level was positively associated with zone1 (winter) but negatively with zone3 (fall). Sandpipers were positively associated with zone4. Abundance distribution maps of conservation-related species, created by inverse distance-weighted interpolation modeling, also showed high abundance of most conservation-related species at zone4 and 1. The findings of our study suggest the importance of natural/semi-natural habitat, and the possible link between human activity and distribution patterns of migratory birds in Gochang getbol. While we need further investigation on direct response of migratory birds to human activity, areas with low human activity with more natural/semi-natural habitat, e.g., zone4 and zone1 may be crucial for the conservation of migratory birds.

Assessing shorebird mortalities due to razor clam aquaculture at key migratory stopover sites in southeastern China

Aquaculture can provide foraging habitat for birds, but it can also result in intentional and accidental mortality. We examined an overlooked conflict between razor clam (Sinonovacula spp.) aquaculture and declining shorebirds in southeastern China's Fujian and Zhejiang provinces. We surveyed 6 out of 11 internationally important stopover sites for these shorebirds and monitored shorebird mortality in 2 sites (Xinghua Bay, Yueqing Bay) with razor clam aquaculture. We visited an additional 32 sites in these 2 provinces to determine if there was netting in other razor clam farms. Approximately 8-9 km2 of intertidal foraging habitat was covered by horizontal nets to prevent birds from feeding on young razor clams at Xinghua Bay and Yueqing Bay. We conservatively estimated that 13,676 (2.5th-97.5th percentile 8,330-21,285) individual shorebirds were entangled in the nets at the 2 monitored sites in April and May 2021, including 2 endangered and 7 near-threatened species. Mortality of 5 species for which we had sufficient data accounted for 0.76% (black-tailed godwit [Limosa limosa]) to 4.27% (terek sandpiper [Xenus cinereus]) of their total flyway populations. This level of mortality could strongly affect their populations. We found netting at 17 additional razor clam farms, indicating a widespread threat to shorebirds. Although razor clams are typically harvested in late March to early April, nets are left on the mudflats throughout the spring and summer, including when the bulk of shorebird migration takes place. Immediately removing these nets after the clam harvest could prevent most of the spring mortality of shorebirds, although this is unlikely to happen without government regulations or economic incentives. To better assess and mitigate the impacts of this conflict, future research should quantify shorebird mortality at other razor clam farms, including during winter, explore less harmful deterrence methods, and assess the socioeconomic factors driving the conflict.

Importance of habitat heterogeneity in tidal flats to the conservation of migratory shorebirds

Understanding species distribution patterns and what determines them is critical for effective conservation planning and management. In the case of shorebirds migrating along the East Asian-Australasian Flyway (EAAF), the loss of stopover habitat in the Yellow Sea region is thought to be the primary reason for the precipitous population declines. However, the rates of decline vary considerably among species, and it remains unclear how such differences could arise within a group of closely related species using apparently similar habitats at the same locales. We mapped the spatial distributions of foraging shorebirds, as well as biotic (benthic invertebrates consumed by migrating shorebirds) and abiotic (sediment characteristics) environmental factors, at a key stopover site in eastern China. Five of the six sediment characteristics showed significant spatial variation with respect to distance along the shoreline or distance from the seawall in the same tidal flat. The biomasses of four of the six most abundant benthic invertebrates were concentrated in the upper or middle zones of the tidal flat. The distribution patterns of all three focal shorebird species on the tidal flat were best explained jointly by this heterogeneity of sediment characteristics and invertebrate prey. These results suggest that the loss of tidal flats along the Yellow Sea, which is typically concentrated at the upper and middle zones, may not only reduce the overall amount of staging habitat, but also disproportionately affect the most resource-rich portions for the birds. Effective conservation of shorebird staging areas along the EAAF and likely elsewhere must consider the subtle habitat heterogeneity that characterizes these tidal flats, prioritizing the protection of those portions richest in food resources, most frequently used by focal bird species, and most vulnerable to anthropogenic threats. Article impact statement: Heterogeneity of tidal flats with respect to biotic and abiotic factors must be considered in shorebird conservation planning.

Assessment of eutrophication from Xiaoqing River estuary to Laizhou Bay: Further warning of ecosystem degradation in typically polluted estuary

The coast of Laizhou Bay is plagued by a number of environmental issues, such as eutrophication, which are likely to worsen over the next few decades as a result of trends toward industrialization and urbanization. High nutrient levels in the Xiaoqing River are believed to be the main cause of Laizhou Bay becoming eutrophicated. Therefore, we conducted two cruises from the Xiaoqing River estuary to Laizhou Bay in August 2022 and December 2022, respectively, in the wet and dry periods to assess the potential impact of status of eutrophication due to human activities. The results showed that the concentration of DIN was higher than the quality standard for water (f_i > 1) in both the wet season (August 2022) and the dry season (December 2022). DIN has major environmental impacts in Laizhou Bay. The eutrophication level index and organic pollution index have obvious spatial and temporal characteristics. In terms of time, the dry season is higher than the wet season. In space, Xiaoqing estuary is higher than Laizhou Bay. In the two surveys, DIN and DIP concentrations were significantly positively correlated, indicating that N and P pollution in the region had a common source and destination, and the spatial distribution was also similar. In addition, the current environmental conditions in the region are not ideal, reaching moderate and severe eutrophication levels, which proves that the ecosystem has the risk of aggravating degradation. As the Xiaoqing River is about to resume full navigation, human-related nutrient input (especially DIN) will continue to increase, and it is expected that the eutrophication risk in this area will increase in the next few years due to the increase in nutrient load.

Effects of aquaculture on the maintenance of waterbird populations

The global aquaculture industry has expanded rapidly and is increasingly important for maintaining food security while also providing alternative artificial habitats for many waterbirds. Clarifying how waterbirds use aquafarms and how aquafarm use affects waterbird population maintenance can be useful for improving management of the artificial landscape that can also provide waterbird habitat. Here, we investigated aquafarm use by waterbirds in China, the world's largest producer of aquaculture products, supported by literature review and questionnaire survey. We used Bayesian phylogenetic generalized linear mixed models to analyze the relationship between the degree of aquafarm use and population trends of waterbirds. The results showed that 69% of waterbird species in China have been recorded at aquafarms. Approximately one-quarter of all waterbird species and about the same proportion of threatened species were found to forage at aquafarms, consuming either cultured aquatic products or other food types. In general, species with a high degree of aquafarm use were unlikely to exhibit a population decline over the past two decades, when rapid loss of natural habitats occurred in China. This relationship was not detected in threatened species, despite there being no significant difference in the degree of aquafarm use between threatened and non-threatened species. Our study suggests that the large and expanding aquaculture industry is important for maintaining waterbird populations in China. However, aquafarms are not a replacement for natural habitats, because threatened species benefit less from aquafarm use. Given that aquafarms often come at the expense of natural wetlands, the degree to which aquafarms compensate for natural habitat loss probably depends on the quality of aquafarm habitat. We recommend an integrated ecological and economic analysis for formulating management policies that help conserve wildlife within the constraints and opportunities associated with maintaining human livelihoods. This article is protected by copyright. All rights reserved.

Unravelling processes between phenotypic plasticity and population dynamics in migratory birds

Populations can rapidly respond to environmental change via adaptive phenotypic plasticity, which can also modify interactions between individuals and their environment, affecting population dynamics. Bird migration is a highly plastic resource‐tracking tactic in seasonal environments. However, the link between the population dynamics of migratory birds and migration tactic plasticity is not well‐understood.

The quality of staging habitats affects individuals' migration timing and energy budgets in the course of migration and can consequently affect individuals' breeding and overwintering performance, and impact population dynamics. Given staging habitats being lost in many parts of the world, our goal is to investigate responses of individual migration tactics and population dynamics in the face of loss of staging habitat and to identify the key processes connecting them.

We started by constructing and analysing a general full‐annual‐cycle individual‐based model with a stylized migratory population to generate hypotheses on how changes in the size of staging habitat might drive changes in individual stopover duration and population dynamics. Next, through the interrogation of survey data, we tested these hypotheses by analysing population trends and stopover duration of migratory waterbirds experiencing the loss of staging habitat.

Our modelling exercise led to us posing the following hypotheses: the loss of staging habitat generates plasticity in migration tactics, with individuals remaining on the staging habitat for longer to obtain food due to a reduction in per capita food availability. The subsequent increasing population density on the staging habitat has knock‐on effects on population dynamics in the breeding and overwintering stage. Our empirical results were consistent with the modelling predictions.

Our results demonstrate how environmental change that impacts one energetically costly life‐history stage in migratory birds can have population dynamic impacts across the entire annual cycle via phenotypic plasticity.