| Assessment of aquaculture carrying capacity is an important basis for scientific planning of aquaculture scale,rational adjustment of aquaculture structure and promotion of modern development,which has attracted extensive attention in recent years.There are many methods for assessment shellfish aquaculture capacity,such as "static" empirical method,instantaneous growth rate,energy budget method and "dynamic" ecosystem dynamics model method.From the core parameters of assessment method,food source is the most important parameter for assessment the carrying capacity of filter-feeding shellfish aquaculture.Current methods for assessing aquaculture carrying capacity mostly use total chlorophyll-a as the driving parameter.Studies have shown that most filter-feeding shellfish can not effectively retain phytoplankton smaller than 2μm due to the gill filament structure.With the deepening understanding of the biogeochemical cycling process and mechanism of aquaculture ecosystem,the characterization of key biological and ecological processes involved in aquaculture carrying capacity assessment tends to be refined.In this context,three typical filter-feeding shellfish,namely Crassostrea gigaslong,Chlamys farreri and Mytilus coruscus,were selected to investigate the retention efficiency of three shellfish for different particle sizes.Investigated the spatial and temporal distribution of the size fraction of phytoplankton,the abundance and biomass of pico-plankton in large-scale bivalve mariculture area.The ecological contribution of the main components of the microbial loop to the Crassostrea gigas was studied by in situ Flow-through Method.The results provide important theoretical basis and data support for further understanding the structure and function of aquaculture ecosystem and effectively improving the accuracy of aquaculture capacity assessment.The main results are as follows:1.The retention efficiency of three important filter-feeding shellfish on sizes fractionated particle.We conducted experiments use in situ Flow-through Method in July and September 2018,respectively.The results show that,in the range of 2-30μm,the standard retention efficiency of three kinds of shellfish increases with the increase of particle size.The average standard retention efliciencies of Crassostrea gigaslong,Chlamys farreri and Mytilus coruscus is 85%,71%,and 85%in summer and 91%,79%,and 84%in autumn,respectively.Compared with the other two species,Chlamys farreri had a lower retention efficiency for small particle size,9.60%for<2μm in summer,and 49%in Crassostrea gigaslong and Mytilus coruscus.2.The spatial and temporal distribution of size fractionated phytoplankton in typical large-scale bivalve mariculture areaFrom 2017 to 2018,a total of 10 field cruises were conducted in Sanggou Bay,Jiaozhou Bay and Zhangzidao Island,and the spatial and temporal distribution of size fractionated phytoplankton were obtained.(1)Distribution of size-fractionated phytoplankton and its relationship with environmental variables in Sanggou Bay.Results showed that the chlorophyll-a concentration in the surface and bottom layers ranged from 0.74-3.27μg/L and 0.81-3.66μg/L,respectively,with the average values of 1.90±1.28μg/L and 2.01q1.29μg/L.There were significant differences in both chlorophyll-a concentration(P<0.01)and spatial distribution between seasons.In spring,micro-phytoplankton was the most abundant,which accounted for 54.05%and 58.08%of the total phytoplankton,respectively in both surface and bottom layers.In summer,the pi co-phytoplankton was most abundant,which accounted for 24.46%and 20.70%of the total cholorophyll-a,respectively.In autumn,the pico-phytoplankton accounted for 35.88%and 40.77%of the total cholorophyll-a in surface and bottom respectively.The contribution of pico-phytoplankton was low in winter and spring but increased significantly in summer and autumn.Redundancy analysis(RDA)results show that temperature is the main environmental factor affecting the size structure of phytoplankton.Dissolved oxygen had a significant effect on the percentage of pico-phytoplankton to total phytoplankton.The percentage of nano-phytoplankton correlated with NO2-and NH4+.There was a significant positive correlation between temperature and the percentage of micro-phytoplankton.This study provided basic knowledge for understanding the size structure of phytoplankton and estimating the carrying capacity of filter-feeding shellfish in the aquaculture ecosystem in Sanggou Bay(2)Seasonal and spatial variations of different size-fractionated phytoplankton in the surface layer of Jiaozhou BayThe chlorophyll-a concentration in the surface layers of Jiaozhou Bay with the average values of 3.33μg/L.There were significant differences in both chlorophyll-a concentration(P<0.01)and spatial distribution between seasons.In spring,the average concentration of chlorophyll-a was 2.09 ug/L.The contribution of micro-phytoplankton,nano-phytoplankton and pico-phytoplankton to total phytoplankton was 15%,81%and 4%,respectively.In summer,the average value of phytoplankton is 4.72 ug/L,and the ratio of size fractionated phytoplankton to total phytoplankton is consistent with spring.In autumn,the average concentration of chlorophyll-a was 2.23 μ1gL.micro-phytoplankton and nano-phytoplankton were dominant,and accounted for 37%and 56%,respectively.In winter,the average concentration of chlorophyll-a is 4.28μg/L.And it is still dominated by nano-phytoplankton,accounting for 55%,and the contribution of pico-phytoplankton is the smallest,only 4%(3)Seasonal and spatial variations of different size-fractionated phytoplankton in the surface layer of Zhangzidao IslandIn August 2017,the average concentration of total chlorophyll-a was 0.71 μg/L,of which micro-phytoplankton,nano-phytoplankton and pico-phytoplankton were 0.12μgL,0.46 μgL,and 0.14 μg/L,and they account for 16%,65%,and 19%of total phytoplankton,respectively.In August 2018,the average concentration of total chlorophyll-a was 1.00 μg/L,of which micro-phytoplankton,nano-phytoplankton and pico-phytoplankton were 0.13 μg/L,0.75 μg/L,and 0.12 μg/L,and they account for 13%,75%,and 12%of total phytoplankton,respectively3.The spatial and temporal distribution of picoplankton and its relationship with environmental variables in Sanggou BayWe conducted four surveys of the Sanggou Bay in 2017-2018,and obtained the temporal and spatial distribution of Synechococcus,Picoeukaryotes and Heterotrophic Bacteria.The main results are as followsThe average of Synechococcus,Picoeukaryotes and Heterotrophic Bacteria was(2.93±2.29)×103cell/ml,(13.84±12.81)×103cell/ml and(1.03±0.28)×106cell/ml in the surface layer of Sanggou Bay.There were significant differences in both abundance and spatial distribution between seasons(P<0.01).The annual changes of Synechococcus,Picoeukaryotes and Heterotrophic Bacteria have the same trend,that is,the abundance is low in spring and winter,and is significantly increased in summer;the abundance of heterotrophic bacteria is the lowest in winter,and the other seasons are basically consistent.In terms of biomass,among the four surveys,heterotrophic bacteria always dominated,accounting for 73.60-94.56%of the total picoplankton biomass;Picoeukaryotes followed,accounting for 4.77-24.11%;Synechococcus only contributed 0.67-2.30%.The correlation analysis between abundance of picoplankton and environmental factors showed that There was a significant positive correlation between chlorophyll-a,temperature and particulate organic matter and this three kinds of picoplankton.Picoeukaryotes correlated with NO3-and NH4+.4.Contribution of main components of microbial food loop to carbon demand of Crassostrea gigas in S anggou Bay aquaculture ecosystemIn July 2018,the contribution of plankton to the carbon demand of Crassostrea gigas was measured based on a in situ Flow-through Method.The results showed that the ranges of plankton clearance of Crassostrea gigas varied from 0.21 to 2.77 L·g-1·h-1 and increased with the increase of plankton size.The clearance rate of Crassostrea gigas to pico-phytoplankton was much lower than that micro-phytoplankton and nano-phytoplankton(P<0.01).In addition,compared with Nanoflagellates and ciliates,the clearance rate of Crassostrea gigas to pico-plankton were extremely low(P<0.01).Overall,the carbon source of Crassostrea gigas from natural plankton was 6945.84 ug·g-1·d-1.Chlorophyll-a of micro-and nano-phytoplankton was the main carbon source(73.73%).The second carbon source was nanoflagellates and ciliates(18.02%).The contribution of pico-plankton less than 2μm to Crassostrea gigas was the lowest(8.24%). |
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