基于生态系统动力学模型的胶州湾菲律宾蛤仔养殖容量动态评估

Dynamical Ecosystem Model-Based Carrying Capacity Estimation for Manila Clam(Ruditapes philippinarum)in Jiaozhou Bay

养殖容量评估是衡量贝类养殖活动是否环境友好、碳汇功能能否充分发挥的重要前提。本研究基于2018年5月—2019年2月的走航观测和定点连续观测数据,通过构建营养盐–浮游植物–浮游动物–碎屑–菲律宾蛤仔(nutrients–photoplankton–zooplankton–detritus–clams,NPZD-C)生态系统动力学模型,动态评估了胶州湾菲律宾蛤仔(Ruditapes philippinarum)的养殖容量。结果显示,构建的生态系统动力学模型能够较好地反演菲律宾蛤仔的生长和浮游植物的动态响应,菲律宾蛤仔和浮游植物的实测值和模拟值均呈显著线性相关(P<0.01),R^(2)分别为0.9348和0.9264;不同放苗密度情境下的产量模拟结果显示,当苗种(2000~3000 ind./kg)的初始放苗密度分别为300、500、700、1000、1500 ind./m^(2)时,蛤仔的预测产量分别为10.5、15.6、18.9、21.6、23.2 t/hm^(2);养殖容量评估结果显示,若在期望的10个月养殖时间内收获湿重为5 g以上的商品蛤仔,放苗密度需控制在1000 ind./m^(2)以内,以生态效益和经济效益的最大化为判定标准,适宜的放苗密度为550~750 ind./m^(2)。研究结果可为实施生态系统水平的胶州湾菲律宾蛤仔养殖管理、充分发挥菲律宾蛤仔的碳汇功能提供理论依据和科学指导。

In recent years,aquaculture has rapidly developed in many countries,playing a positive role in ensuring food security and promoting economic development.However,it has also produced negative effects,such as water pollution and eutrophication.As the key species in integrated aquaculture systems,bivalves not only improve space utilization and provide economic benefits,but also regulate nutrient cycling,reduce water body eutrophication,increase the ability of blue carbon sinks to capture and hold carbon,improve system stability,and perform various ecosystem services,including nutrient removal and carbon sequestration.However,as a resource-dependent aquaculture industry,high-density and unreasonable bivalve aquaculture produces a strong downlink control effect on the phytoplankton community structure,which in turn restricts the carbon sink function of shellfish aquaculture ecosystems and negatively affects the ecosystem.China is the dominant country in terms of shellfish farming.In 2020,the total output of marine shellfish was 14.80 million tons,ranking first in the world.In China,the main target of marine shellfish farming is bivalves,which account for 95%of the total marine shellfish output.The total output of Ruditapes philippinarum is over 3 million tons,accounting for 90%of the global output.Jiaozhou Bay is an important large-scale aquaculture base for R.philippinarum in northern China,with a clam output of 325000 tons,accounting for 91.5%of the total output from this base.In April 2017,the core purpose of the proposal for the Chinese Academy of Engineering entitled"Proposal on Promoting Green Development of Aquaculture Industry"was to call for the establishment of an aquaculture capacity management system.In this context,research on the carrying capacity of shellfish is of theoretical and applied significance.The ecosystem dynamics approach assesses carrying capacity based on different evaluation criteria by constructing ecosystem models to simulate key biogeochemical processes and their interactions with important biogenic elements.As our understanding of the concept of carrying capacity and ecosystem structure and function continues to improve,ecosystem dynamics methods that can describe in more detail the physical,biological,and chemical processes and their interactions involving culture organisms in aquaculture ecosystems have become the mainstream direction for global carrying capacity researchers.Although these methods are now widely used in several aquaculture bays around the world,they remain rare in China.We estimated the carrying capacity of R.philippinarum in Jiaozhou Bay based on the Dame indices and Herman model,although the assessment method used portrayed coarse lines of ecological processes,which mainly considered shellfish feeding on phytoplankton,lacking the depiction of other biological roles,and the core parameters were not sufficiently comprehensive.In the present study,the individual growth model for R.philippinarum and a biogeochemical model were coupled to build the nutrient–phytoplankton–zooplankton–detritus–clams(NPZD-C)dynamic ecosystem model of Jiaozhou Bay,and the carrying capacity of R.philippinarum was estimated dynamically.The individual growth model for R.philippinarum in Jiaozhou Bay was constructed based on the dynamic energy budget(DEB)theory following model parameterization and validation.The simulated results from the dynamic ecosystem model well fit the observed results.Regression analysis showed a significant(P<0.01)linear correlation between the simulated and observed values of clam wet weight and phytoplankton concentration(R^(2)=0.9348 and 0.9264,respectively).The results of carrying capacity estimation showed that the final clam yield was 10.5,15.6,18.9,21.6,and 23.2 t/hm^(2) and the maximum phytoplankton(carbon)concentration was 231.3,176.9,147.6,125.1,and 109.8 mg/m^(3) when the initial seeding density was 300,500,700,1000,and 1500 clams/m^(2),respectively.Of note,carrying capacity assessed based on the ecosystem dynamics model varies depending on concerns regarding environmental quality,yield,and economic benefits,and there is no uniform standard.In the present study,the criteria used for the assessment of carrying capacity included the maximum stocking density to achieve the minimum size of commercial shellfish and the aquaculture density to maximize economic benefits within a limited period.Our assessment results can help farmers develop aquaculture management strategies.The seeding density should be less than 1000 clams/m^(2) if individuals with a wet weight of 5 g or more are harvested within the expected 10-month aquaculture period.According to the maximum economic and ecological benefits,the most suitable seeding density is 550~750 clams/m^(2).This study attempted to construct the NPZD-C ecosystem dynamics model for Jiaozhou Bay by coupling the individual growth model for R.philippinarum and a biogeochemical model and assess the carrying capacity of R.philippinarum in Jiaozhou Bay by considering economic and ecological benefits as the assessment criteria,proposing farming management suggestions for clam seeding density.The results are expected to provide data support and reference in decision-making for planning the development of the local R.philippinarum aquaculture industry and provide a theoretical basis and scientific guidance for managing shellfish aquaculture at the ecosystem level and exploiting the carbon sink function of shellfish.