Impacts of shellfish aquaculture on the ecological carrying capacity of Portunus trituberculatus in Laizhou Bay

In this study, we constructed an Ecopath model of the artificial reef ecosystem in Laizhou Bay, with special emphasis on the stock enhancement opportunities. Laizhou Bay is the largest semi-enclosed bay in the Bohai Sea, China, where multiple factors, especially overfishing, have led to the decline of many commercial marine fish stocks. Artificial oyster reefs were developed in 2011 in this region, providing shelter, feeding, and breeding sites for marine organisms. Additionally, stock enhancement by release can be used to replenish fishery species resources. Ad hoc stock enhancement, however, can fail to bring economic benefits and may impact ecosystem stability. Therefore, we estimated the ecological carrying capacity of the three main economic fish species in Laizhou Bay, including black rockfish (Sebastes schlegelii), fat greening (Hexagrammos otakii), and Chinese seabass (Lateolabrax maculatus) before release to ensure the sustainable use of fishery resources. The Ecopath model in Laizhou Bay was divided into 17 functional groups based on commercial relevance, dietary similarity, and habitat needs of the species present in the area. The ecological parameters, such as the ratio of total primary productivity to total respiration (1.205), connectance index (0.207), and system omnivory index (0.090) indicated that the artificial reef ecosystem in Laizhou Bay has a relatively simple food web structure. The ecological carrying capacities of S. schlegelii, H. otakii, and L. maculatus were assessed at 0.4676 t/km2, 0.5472 t/km2, and 0.3275 t/km2, respectively. This study provides a reference for the formulation of fishery strategies to maintain ecosystem stability and biodiversity and to maximize fishery returns and sustainability in Laizhou Bay.

Laizhou Bay’s coastline has undergone multiple alterations due to human activities such as land reclamation and port construction. These changes in the coastline have led to modifications in the bay’s hydrodynamic conditions, which, in turn, can impact the marine environment and potentially result in a decline in biodiversity. To date, there has been no comprehensive study focusing on the coastline changes and hydrodynamic variations in Laizhou Bay. Therefore, this study utilizes coastline and water depth data from four time points—1990, 2003, 2013, and 2023—to establish a two-dimensional tidal current model of Laizhou Bay using Delft3D. Based on the good agreement between the simulated tidal current results and the observed data, this study further investigates the changes in tidal prism and water exchange in Laizhou Bay. The results indicate that tidal currents dominate the bay, with significant influences of topographic changes on the velocity and direction of tidal flows. The Eulerian residual current velocity is substantially lower than the tidal current velocity. Both tidal and residual currents play a role in controlling the distribution of materials within Laizhou Bay. Over the past three decades (1990-2023), the tidal prism in Laizhou Bay has shown a downward trend, with the tidal prism during spring, intermediate, and neap tides in 2023 reduced by 2.03%, 6.36%, and 10.19%, respectively, compared to 1990. The water exchange capacity has also weakened, with the half-exchange time being 71 days in 1990, increasing to 73 days in 2003 and 81 days in 2013, and showing a slight increase of 1 day in 2023 compared to 2013. Thus, changes in the coastline and water depth of Laizhou Bay can alter its hydrodynamic conditions, significantly impacting the tidal prism and water exchange, leading to a decrease in tidal prism and exchange rate, an increase in the water exchange period, a slower dispersion rate of pollutants, and a reduced water environmental carrying capacity. This research provides a scientific reference for protecting the marine environment and coastal management in Laizhou Bay.

Biological characteristics, density and its spatial distribution of Portunus trituberculatus in Laizhou Bay, together with the impact of environmental factors, were analyzed based on the bottom trawl data of 9 surveys from May 2011 to April 2012, in order to provide scientific basis for utilizing and protecting the resource of P. trituberculatus. The monthly variation of biomass density could be described as September > October > July > August > June > November > March > May > April. The average values were highest in August 2011 and lowest in April 2012, for body mass, width and length, respectively. The individual fatness coefficient was highest in August 2011 both for the female (1.030) and the male (1.023), lowest in July both for the female (1.007) and the male (1.007). The difference of fatness coefficient was not significant (P>0.05) between the female and the male. The sex ratio (female/male) was less than 1.0 in most of all months except June, July and August. P. trituberculatus was mainly distributed in the Yellow River estuary and the offshore off Longkou in May-July, in offshore off Weifang and Longkou in August-September, and in deep-water area of the Laizhou Bay mouth from October to next April. Pearson correlation analysis indicated that environmental factors that best matched the density of P. trituberculatus were sea surface temperature (SST), dissolved oxygen (DO) and water depth (Dep), followed by salinity (Sal) and zooplankton density, the last were phytoplankton density and the number of other demersal fisheries species. The body length of P. trituberculatus in 2011 was significantly smaller (P<0.01) compared with that in 1981. To sustainably utilize the resource of P. trituberculatus in Laizhou Bay, we suggested that the fishing effort should be reduced, the catchable size should be raised, the research of enhancement basements should be promoted and more reasonable releasing quantity should be proposed.

Large-scale seaweed and shellfish aquaculture are increasingly being considered by policymakers as a source of food, animal feed and bioproducts for Europe. These aquacultures are generally thought to be low impact or even beneficial for marine ecosystems as they are ‘extractive’ – i.e., growing passively on foodstuff already available in seawater, and with potential habitat provision, fisheries, climate mitigation and eutrophication mitigation benefits. At some scale however, over-extraction of nutrients or chlorophyll could potentially have a negative effect on natural systems. Understanding the likely impacts of aquaculture production at scale is important to identify when safe limits are being approached. Taking seaweed aquaculture as the primary focus, this work uses operational oceanographic model outputs to drive prognostic growth models to predict the likely optimal distribution of seaweed farms across European waters to meet different production scenarios. A novel nutrient transport scheme is then used to model the interacting ‘footprints’ of nutrient drawdown from aquaculture facilities to demonstrate the likely spatial impact of large-scale aquaculture. Evaluation of both seaweed and shellfish contributions to CO2 balance under large scale production, and the potential impact on fisheries are also considered. The study finds that the impact of intensive seaweed aquaculture on nutrient availability could be significant where many farms are placed close together; but at the regional/basin scale even the highest level of production considered does not significantly impact total nutrient budgets. Seaweed aquaculture has the potential to extract large amounts of carbon dioxide, but the impact on carbon budgets depends on the end-use of the extracted seaweed. Shellfish aquaculture is a net source of CO2 due to the impact of calcification of shells on the carbonate system (i.e., alkalinity removal). However, gram-for-gram the CO2 impact of shellfish production is likely to be less than the impact of land-based meat production. Whilst operational oceanographic models are useful for taking a ‘broad brush’ approach to likely placement and impacts of aquaculture, reliable yield predictions for individual locations across European waters would require models integrating more physical and biogeochemical factors (wave environment, local currents, riverine inputs) at a finer scale than currently achievable.

Assessment of ecological security is essential for understanding the status of bay ecosystem and developing appropriate management strategy. Based on the driving force-pressure-state-impact-response (DPSIR) model, the demographic, economic, social, and ecological data of Laizhou Bay and its three neighboring counties were selected for the period from 2015 to 2021. An ecological security evaluation index system of Laizhou Bay containing 26 indicators was established, and the weights of each indicator were determined by the methods of AHP and EWM, and a comprehensive evaluation of the ecological security of Laizhou Bay was carried out by ESI. Correlations between indicators were analyzed by the Spearman's rank coefficient of correlation. The results showed that there were significant correlations between marine conditions and indicators such as population size in the surrounding area, mariculture area, industrial and domestic wastewater discharge, and treatment rate. Overall, from 2015 to 2021, the ecological security of Laizhou Bay showed a favorable trend, from a relatively unsafe level to a generally safe level, and then to a relatively safe level. Through the comprehensive evaluation of the ecological security of Laizhou Bay, we can recognize the utilization of marine resources and ecological carrying capacity, guide the rational development and utilization of marine resources, and promote the sustainable development of the marine economy.

Intense development has been occurring along the shores of the Bohai Sea that threatens to increase local levels of pollution. A need existed to extract the coastline data of the Bohai Sea from remote sensing images to document changes in the coastline. Landsat imagery from 2000 and 2016 was used to analyze the temporal-spatial changes along this coastline. The results showed that the total length of the coastline increased by 1 111.5 km (40&#x0025;) during this period. In addition, development has caused the conversion of natural coastline to man-made coastline, and the length of total man-made coastline increased by 1 532.9 km. Among three bays (Bohai, Liaodong, and Laizhou bay), Bohai Bay experienced the greatest increase in the coastline. The lengths of total coastline and the related man-made coastline both doubled a change that also involved a drastic reduction in sea area. The total area of the Bohai Sea declined by 2 360 km2 from 2000 to 2016 to 75 200 km2. Bohai and Laizhou bays both experienced a nearly 10&#x0025; reduction in their respective original areas. Specifically, Bohai Bay lost 1 165 km2 of area, accounting for half of the total reduction in the area of the Bohai Sea during this time period. More than 95&#x0025; of lost sea area was converted to enclosures for aquaculture or used for the construction of harbors, docks, and industrial parks. The reduction of sea area and changes in the hydrodynamic environment will affect the environmental carrying capacity of the Bohai Sea.

We evaluated genetic diversity and differentiation among five wild populations of the swimming crab(Portunus trituberculatus) using eight polymorphic microsatellite loci.We collected crabs from Zhoushan(ZS),Haizhou Bay(HZ),Huichang(HC),Laizhou Bay(LZ),and the mouth of the Yalu River(YL).We isolated 72 alleles from eight loci among the five populations.The number of alleles ranged from 6 to 12 and the average number of alleles(A) and effective numbers of alleles(Ne) were 9.0 and 5.467 7,respectively.The mean PIC value for the eight microsatellite loci was 0.696 7.The expected heterozygosity(He) of each population was as follows: LZ(0.770 4),HC(0.758 8),YL(0.755 2),HZ(0.741 5),and ZS(0.728 3).The observed heterozygosity(Ho) was between 0.648 1 and 0.760 4.Six loci deviated significantly or very significantly from Hardy-Weinberg equilib-rium.The genetic distances among populations ranged from 0.245 1 to 0.517 9.The UPGMA tree suggested that there were two different groups: one being composed of YL and LZ,and the other of HC,HZ and ZS.The Fst values ranged from 0.054 8 to 0.108 3,suggesting that the degree of differentiation was moderate among the five wild populations(0.05Fst0.15).

In this study, we investigated the community structure of crustaceans (decapod and stomatopod) inhabiting the sandy mud bottoms of Laizhou Bay (northeastern China) monthly from May 2011 to April 2012. Investigation was stopped from December 2011 to February 2012 because of the extreme weather and sea ice. A total of 205,057 specimens belonging to 31 species (shrimp, 15; crab, 15; and stomatopod, 1) were collected in 148 hauls. From 2011 to 2012, Oratosquilla oratoria was the dominant biomass species (47.80%), followed by Charybdis japonica (15.49%), Alpheus japonicas (12.61%), Portunus trituberculatus (6.46%), and Crangon spp. (4.19%). Crangon spp. was the most dominant species by individual (32.55%). O. oratoria was the most-frequently encountered species (81.76%), followed by Palaemon gravieri (70.95%), C. japonica (65.54%), A. japonicas (62.16%), and P. trituberculatus (54.73%). The biomass density increased from August to September 2011 and decreased from March 2012 to April 2012. The dynamics of the ecological indices evolve in a similar manner, with high values of diversity and evenness and rich species from May to June 2011 and low values from September to October 2011. O. oratoria, C. japonica, and P. trituberculatus differed by biomass data between groups I (samples obtained from September to October 2011) and II (samples in other months). These species contributed more than 70% to the similarity of the crustacean community structure. Furthermore, the subsets of environmental variables that best matched the crustacean-assemblage structure were as follows: water depth (WD) in summer (June to August); sea surface temperature (SST), dissolved oxygen (DO), and WD in autumn (September to November); and DO, salinity, and WD in spring (March to May). The calculated correlation coefficients and significance level were higher in the period of July to August 2011 than in other months. Comparing 2011 to 2012 with 1982 to 1983, the species composition remained stable. However, the dominant species changed significantly. High value and large species, such as F. chinensis, P. trituberculatus, and T. curvirostris, have been replaced by low value and small species (i.e., Crangon spp., P. gravieri, and C. japonica).

The direct and indirect impact of fish farms, shellfish aquaculture, and extensive forms of aquaculture such as seeding of juvenile sea urchins, on macrophytes (seaweeds and seagrasses), is reviewed in Mediterranean benthic ecosystems. Fish farms constitute a source of organic matter and nutrients (food and fecal pellets) that causes the extirpation of Posidonia oceanica seagrass meadows beneath and near to farm facilities. In addition to direct effects, the nitrogen enrichment of macrophytes tissues increases the grazing pressure by herbivorous fishes and sea urchins. In some cases, the impact can continue to increase several years after the cessation of farming activities. Natural restoration of extirpated seagrass meadows is generally unlikely at the human time scale. Shellfish aquaculture is the cause of the main flow of introduced macrophytes in the Mediterranean; the main vector is the importation of oyster spat from Japan and Korea. North-eastern Pacific seaweeds are now the dominant biotic component of some Mediterranean lagoons (e.g., Thau, Mar Piccolo and Venice lagoons). In addition to direct effects, mussel aquaculture can constitute a source of larvae that flow with currents, the adults of which can overwhelm seaweed forests (e.g., Carpodesmia mediterranea). Shellfish aquaculture is also a source of fecal pellets, resulting in changes in bottom macrophytes, and a vector of diseases of metazoans, the extirpation of which may change the functioning of recipient macrophyte ecosystems. The edible sea urchin Paracentrotus lividus is sometimes erroneously considered as in decline due to over-harvesting. However, its abundance in the second half of the 20th century was probably a consequence of human impact (overfishing of its predatory fish, organic pollution. This man-induced proliferation resulted in the extirpation of seaweed forests (e.g., Carpodesmia spp., Treptacantha spp. – formerly Cystoseira spp. – Sargassum spp.; many species are endemic), which play a key role in Mediterranean coastal ecosystems. Therefore, the attempts to restore sea urchin abundance, via seeding of juveniles from hatcheries, has further artificialized the habitats rather than contributing to the restoration of natural ecosystems. Good practices guidelines are proposed aimed at minimizing the impact of aquaculture on macrophytes.

In this study,total 35 microsatellite DNA markers were selected to analyze the genetic structure of 110 individuals in an F 2 family which is obtained by directional mating techniques for the selective program on fast growing Portunus trituberculatus.(The F 2 family was created by F 1 family which was generated by wild populations from Laizhou Bay and Zhoushan Island.) The results showed that total 87 different alleles were found,and the number of alleles was 2 to 4 in each locus,with 2.2 effective alleles on average.The value of mean observed heterozygosity,the value of mean expected heterozygosity and the mean Polymorphism Information Content(PIC) was 0.646 5,0.513 0 and 0.449 1,respectively.The probability value of chi-square test showed that most of the loci deviated from Hardy-Weinberg equilibrium significantly.The GLM procedure in SAS9.1 was used to analyze the correlation between these 35 microsatellite markers and growth related traits of P.trituberculatus.The growth related traits included full carapace width,body weight,carapace width,carapace length,body height,second obital margin width,meropodit length of the claw,meropodit length of the first peraeopod.Results indicated that Pot08 had a significant impact on full carapace width,body weight,carapace length,body height,second obital margin width;Pot42 had a significant impact on body weight,carapace length,meropodit length of the claw,meropodit length of the first peraeopod;Pot53 had a significant impact on carapace width and meropodit length of the claw,and had a very significant impact on second obital margin width;Pot57 and PTR30 had a significant impact on meropodit length of the first peraeopod and carapacel length,body weight,respectively;PTR8a had a significant impact on the first peraeopod and carapace length,body height,and had a very significant impact on body weight,second obital margin width,full carapace width and carapace width;PTR131 had a significant impact on body weight,full carapace width and carapacel width.Finally,PTR8a can be used for marker assisted selection which could be used for body weight selection.

Analysis on the utilization and carrying capacity of coastal tidal flat in bays around the Bohai Sea

Models and tools for assessing the carrying capacity of an area of interest for bivalve culture can be classified according to their level of complexity and scope. In this report, we discuss and outline four hierarchical categories of carrying capacity studies: physical, production, ecological, and social carrying capacity. The assessment of carrying capacity for progressively higher categories of models is based on a sound understanding of preceding categories. We discuss each in brief and the third in more detail as this is the level at which knowledge is the most lacking and for which science may make the most advances. (1) Physical carrying capacity may be assessed by a combination of hydrodynamic models and physical information, ideally presented and analysed within a Geographic Information System (GIS). (2) Most scientific effort to date has been directed towards modelling production carrying capacity and some of the resulting models have been used successfully to this end. Further development of these models should pay attention to (i) better modelling of feedback mechanisms between bivalve culture and the environment, (ii) a consideration of all steps in the culture process (seed collection, ongrowing, harvesting, and processing), and (iii) culture technique. (3) The modelling of ecological carrying capacity is still in its infancy. The shortcomings mentioned for models for production carrying capacity estimates are even greater for ecological carrying capacity models. GIS may be employed to consider interactions between culture activities and sensitive habitats. (4) It is recommended that social carrying capacity be evaluated only after the preceding levels have been completed so that an unbiased assessment is obtained. This however does not exclude direction from managers for scientists as to which factors (such as water clarity, specific habitats, etc.) should be evaluated. The use of expert systems to aid in management decisions is briefly discussed with a suggested application of a fuzzy expert system to this end.

Based on the water resource data and economic data from 2006 to 2017, this paper analyzes the temporal and spatial variation characteristics of sustainable water resources utilization in Yan’an, using a water ecological footprint model and the ten-thousand-yuan GDP water resource ecological footprint, combined with the ecological carrying capacity and ecological deficit principle. The result shows that the overall wave of the water resources ecological footprint in Yan’an rises but not in an obvious way, but the ecological carrying capacity and the ecological deficit of water resources are fluctuating. Production water accounts for the largest proportion in the water resources ecological footprint. Affected by industrial transformation, the industrial water consumption in Yan’an has increased year by year and ranked the first by exceeding agricultural irrigation water in 2009. The ecological footprint of water resources in Yan’an has always been greater than its ecological carrying capacity, and the water supply has been in an ecological deficit state; in general, the ten-thousand-yuan GDP water resources ecological footprint has decreased obviously, while the resource utilization has gradually been increasing. However, consumption on water resources by economic development is still faster than resource regeneration.

21世纪以来陕西生态足迹和承载力变化

The carrying capacity concept for bivalve aquaculture is used to assess production potential of culture areas, and to address possible effects of the culture for the environment and for other users. Production potential is depending on physical and production carrying capacity of the ecosystem, while ecological and social carrying capacity determine to what extent the production capacity can be realized. According to current definitions, the ecological carrying capacity is the stocking or farm density of the exploited population above which unacceptable environmental impacts become apparent, and the social capacity is the level of farm development above which unacceptable social impacts are manifested. It can be disputed to what extent social and ecological capacities differ, as unacceptable impacts are social constructs. In the approach of carrying capacity, focus is often on avoiding adverse impacts of bivalve aquaculture. However, bivalve populations also have positive impacts on the ecosystem, such as stimulation of primary production through filtration and nutrient regeneration. These ecosystem services deserve more attention in proper estimation of carrying capacity and therefore we focus on both positive and negative feedbacks by the bivalves on the ecosystem. We review tools that are available to quantify carrying capacity. This varies from simple indices to complex models. We present case studies of the use of clearance and grazing ratio’s as simple carrying capacity indices. Applications depend on specific management questions in the respective areas, the availability of data and the type of decisions that need to be made.