Changes Of Environmental Factors And Their Effects On Phytoplankton In The Scallop Culture Area Of Yantai

The physicochemical factors,nutrients,microorganisms and phytoplankton in 11scallop culture areas of Yantai were investigated for 8 voyages from April to November in2016.The indicators included:pH value,water temperature,salinity,dissolved oxygen,chemical oxygen demand,sulfide,inorganic nitrogen(nitrate,nitrite and ammonia nitrogen),total nitrogen,active phosphorus,total phosphorus,chlorophyll a,heterotrophic bacteria and Vibrio.The community composition and quantity of phytoplankton were detected by microscope.The following are the results of the study.The variation range of p H value in 11 scallop culture areas is 7.79~8.25,which is weak alkaline in general,and all meet the national water quality standards 1 and 2.The range of water temperature and salinity range are 10.1~28.7?and 29.13~30.313,respectively,which are within the optimum growth salinity range of bay scallop.The variation range of dissolved oxygen is 6.16~9.90 mg/L,which shows that the content of dissolved oxygen decreases with the increase of water temperature.The variation range of chemical oxygen demand is 0.48~2.76 mg/L in October,which accords with the second class standard of seawater water quality,and the others accord with the first class standard of national water quality.The variation range of nitrate,nitrite and ammonia nitrogen are0.008~0.413 mg/L,0.001~0.052 mg/Land 0.002~0.134 mg/L,respectively.The ratio of nitrate to total inorganic nitrogen is the largest,the proportion of nitrite is the smallest,the content of ammonia nitrogen is unstable,and the change trend is not obvious.The range of active phosphorus varies from 0.002 to 0.034 mg/L,and in October,the water quality of individual aquaculture areas exceeded the second class standard of sea water quality.The variation range of total nitrogen and total phosphorus were 0.496~1.324mg/L and 0.012~0.111 mg/L,which were in dynamic change.The organic pollution index of the 11 scallop aquaculture areas was-1.12~0.84,with good water quality and no organic pollution.The variation range of seawater nutrient index and seawater nutrition status index is 0.005~2.340 and 1.98~5.91 respectively,and the individual breeding area is eutrophication,but the degree is relatively low.The comprehensive evaluation of the sea water in the culture area showed that the 11 breeding areas were all in line with the requirements of the I and II areas in the scallop culture area.The range of heterotrophic bacteria varies from 21.5 to 6515 cfu/mL,and some aquaculture areas have a high concentration in April,May and November,and they are at the moderate level of pollution.The variation range of Vibrio is 0.5 to 43.5 cfu/mL,which is at a low level compared with other culture areas,and has little effect on scallop culture,which is not enough to cause scallop diseases.Correlation analysis shows that there is a very significant positive correlation between Vibrio and Chemical oxygen demand,activated phosphorus,total phosphorus,organic pollution index(A)and nutritional index(E)and seawater nutrient quality index(NQI)showed a significant positive correlation(p<0.01),which revealed the organic matter,phosphate and environmental pollution situation is conducive to the growth of Vibrio,attention should be paid to the detection in this respect.98 species in 5 phyla of phytoplankton were found during the investigation,including 63 species of Bacillariophyta,14 species of Pyrrhophyta,11 species of Chlorophyta,5 species of Chrysophyta and 5 species of Cryptophyta.Different Scallop in Shell farming area density and species number of phytoplankton that obvious season variation.The number of phytoplankton density and species showed significant seasonal difference in different scallop culture areas.The dominant species of phytoplankton including Guinardia delicatula,Nitzschia longissima,Nitzschia sp.,Skeletonemaceae costatum,Cyclotella sp.,Chaetoceros sp.,Chroomonas sp..The variation range of phytoplankton density was 4.29×10~3~1120.4×10~3 cell/L,with obvious seasonal difference.The phytoplankton community diversity index varied from 0.35 to 3.96,and the richness index varied from 1.47 to 4.89,and the evenness index varied from 0.11 to0.96.The overall biodiversity was good,the community structure was complex,and the ecological environment was well.Correlation analysis shows that In spring and autumn,there was a positive correlation between water temperature and phytoplankton density and species number,while in summer,there was a significant negative correlation between water temperature and phytoplankton density and species number(p<0.01),which shows that in a certain range of temperature,the increase of water temperature is beneficial to the growth of phytoplankton,but more than this temperature has a inhibitory effect.pH value,salinity,dissolved oxygen and COD had no significant correlation with phytoplankton in different seasons,indicating that these environmental factors had little or no effect on phytoplankton.there is a significant positive correlation between nitrate and phytoplankton density(p<0.01)in spring,both nitrate and inorganic nitrogen were significantly negatively correlated with phytoplankton density and species number(p<0.01)in autumn,compared with nitrogen nutrient,the correlation between phosphorus nutrition and phytoplankton density and species number is more significant,indicating that phytoplankton is more significant for phosphorus nutrition,and phosphorus nutrient has greater impact on phytoplankton,on the other hand,the dissolved inorganic phosphorus in summer and autumn may be a limiting factor for the growth of phytoplankton in Yantai scallop culture area.