| Dimethyl sulfide?DMS?is the most important and abundant volatile biogenic organic sulfide in seawater,which can alleviate global warming.Its precursor is dimethylsulfoniopropionate,mainly in phytoplankton.Filter feeding bivalve is an important ecological group in coastal ecosystem.In order to explore the impact of filter-feeding bivalve mariculture on the production and transfer of DMS?P?,The following work was carried out:1. In this study,the DMS measurement method was the headspace solid phase microextraction-mass spectrometry method.Through optimization experiments,the optimal conditions of the chromatographic column and extraction settings were selected.The Vocol chromatographic column was selected,the extraction temperature was selected at 24?,and the extraction time was selected.20min,the analysis time is 2min,and The adding quantity of Na Cl is 2.5g.The recovery rate of the method is 93%?103%,the relative standard deviation is<7%,the detection limit is 0.11nmol/L and R2is always>0.995 under different concentration gradients.This method meets the needs of experimental determination.2. Phytoplankton is the precursor of DMSP and is the main food for filter-feeding bivalve.The investigation of the characteristics of phytoplankton community in the culture area can provide a reference for laboratory feeding experiments.Four seasonal cruises were carried out in April 2017?Spring?,July?Summer?,November?Autumn?and in January 2018?Winter?in Sanggou Bay,a typical bivalve culture bay.Results showed that 51 species of 31 genus.Phytoplankton were identified in the surveyed area.Among them,there were 43 species from 24 genera of Diatoms,4 species from 3 genera of Dinoflagellates,2 species from 2 genera of Chlorophyta,and 1 species of Cyanophyta.Diatoms were the dominant species.3. Four kinds of common economic filter-feeding bivalves include oyster?Crassostrea gigas?,mussel?Mytilus edulis?,scallop?Chlamys farreri?and clam?Ruditapes philippinarum?,phytoplankton Isochrysis galbana,Chaetoceros muelleri Lemmerman,Nitzschia closterium,Chlorella sorokiniana,Phaeodactylum tricornutum were selected to be fed.Experiments were carried out on mussel feeding on different density of phytoplankton?Isochrysis galbana?,different bivalves feeding on phytoplankton?Isochrysis galbana?,and mussel feeding on different phytoplankton.The variations of DMS?P?in water under the static condition are monitored in laboratory by simulation experiment,Results showed that the production of DMS was not significantly affected by the feeding activity of all kinds of bivalves?P>0.05?under the static condition,but which?40%of the DMSPp intake was converted into feces DMSP?DMSPf?due to ingestion.At the same time,the accumulation effect of mussel feeding activities on DMSP was discussed.Through the experiment of feeding the mussels with phytoplankton?Isochrysis galbana?for 31 consecutive days,it was found that the content of DMSPtissuewas significantly increased,compared with 0.97±1.03?g/g at 0d,the DMSPtissuereached 128.47±80.65?g/g at 30d,while the DMSPtissue of the natural seawater group was 1.06±1.09?g/g,with no significant change.This indicates that the effect of feeding activity on the production and transfer of DMS?P?also includes the accumulation of DMSP by filter-feeding bivalve.4. To understand the effect of filter feeding bivalve feeding activities on the production and transfer of DMS?P?under disturbance conditions,Under laboratory simulation conditions,The change of DMS?P?in the total original water disturbance experiment and quantitative fecal disturbance experiment were discussed.It was found that the DMSPf would diffuse into the water with the disturbance,and then increase the amount of DMSPt and DMS in the water.In the total original water disturbance experiment,compared with the control group?0 rpm?,the DMS and DMSPt in the experimental group could be increased by 16.8%and 38.5 times.The experiment of quantitative fecal disturbance found that in the DMS seawater with quantitative feces,as the degree of disturbance increased,DMS and DMSPt increased,from 7.6 nmol/L and 906.4 nmol/L in the static state to a maximum of 21.3 nmol/L and 2505.9 nmol/L,which increased by 180%and 174%,respectively.5. The distribution of DMS?P?in the bivalve culture area can reflect the impact of filter-feeding bivalve feeding activities on the production and transfer of DMS?P?to a certain extent.The distribution of DMS?P?in the Sanggou Bay area was investigated in May 2019,The results show that the DMSPd and DMSPt in bivalve culture areas were29.10 nmol/L and 43.54 nmol/L,respectively,which were higher than those in the control area 9.27 nmol/L and 25.97 nmol/L.The dissolution and diffusion of bivalve biodeposition may be the reason for this phenomenon,The average DMS concentration in the aquaculture area is 3.97 nmol/L,which is less than 10.20 nmol/L in control area.For this phenomenon,continuous investigation and study are required. |
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