Spatiotemporal Dynamics Of Phytoplankton And Its Relationship With Environmental Factors In The Coastal Water Of Weihai In 2022

With the influence of global change and human activities,toxic and harmful algal blooms have occurred frequently,which has brought many influences and uncertainties to coastal mariculture.Weihai is the city with the longest coastline in China,and the aquaculture industry in the coastal water is developed,but the research on phytoplankton community structure and its changes in the coastal water is relatively lacking at present.Based on the ecological investigation of phytoplankton in spring(April and May),summer(August)and autumn(October)in 2022,this paper studied the phytoplankton community structure,species composition,dominant species,cell abundance and their relationship with different environmental factors in the coastal water of Weihai by using vertical trawling and surface water samples.Combined with different aquaculture species in different sea areas,we analyzed the changes of dominant phytoplankton species,the relationship between red tide outbreaks and aquaculture organisms and their potential hazards,which provided important reference for red tide monitoring and early warning in this sea area.The main results were as follows:1.In this study,155 species of phytoplankton belonging to 64 genera and 3 phyla were found,among which diatom and dinoflagellate were the main groups.Among them,there were 116 species in 49 genera of diatom,38 species in 14 genera of dinoflagellate,and 1 species in 1 genus of silicoflagellate.The number of species found by the two investigation methods was the highest in summer and the lowest in spring.In spring,Coscinodiscus spp.and Paralia sulcata were the common dominant species in the two sampling methods.In summer,the dominance of Chaetoceros spp.and Pseudo-nitzschia spp.was significant,and Eucampia zodiacus was the absolutely dominant species in autumn.2.The average cell abundance of phytoplankton collected by trawl ranged from 0.63 to 30.18×10~3 cells/L,with an average abundance of(2.20±6.15)×10~3 cells/L.The phytoplankton cell abundance in the collected water samples ranged from 0.11×10~3 to 330.81 ×10~3 cells/L,with an average abundance of(29.05±68.74)×10~3 cells/L.The change trend of phytoplankton in the two sampling methods was slightly different.The average cell abundance of phytoplankton collected by trawl was the highest in autumn and the lowest in spring.The average cell abundance of phytoplankton in water samples was the highest in summer and the lowest in spring.3.The Shannon-Wiener diversity index was the highest in autumn and the lowest in spring(May).The Pielou evenness index was the highest in spring(May)and the lowest in summer。On the whole,phytoplankton in the coastal water of Weihai had good community stability.high species diversity and strong anti-interference ability.4.The analysis of the relationship between phytoplankton abundance and community structure and environmental factors showd that the influencing factors of phytoplankton abundance and community structure were different in different seasons.In springphytoplankton abundance,dominant species distribution and salinity showed a significant negative correlation.In summer,phytoplankton abundance was positively correlated with nitrate and negatively correlated with salinity.The environmental factors that significantly affect the dominant species were dissolved oxygen,pH,nitrite and nitrate.There was a significant positive correlation between phytoplankton and chlorophyll A in autumn,and the distribution of dominant species was significantly related to pH and phosphate.5.In summer,in Sanggou Bay in the east,the number of phytoplankton was limited due to super-capacity shellfish culture,and the proportion of dinoflagellate in the community structure was large due to phosphorus limitation.Phytoplankton was significantly affected by nutrients in summer,and the abundant nutrients in the southern Rushan-Wendeng sea area promoted the growth of phytoplankton and diatoms in this sea area.Moreover,the selective feeding of oysters further caused the phytoplankton structure to be dominated by diatoms.In autumn,the floating corner algae was less limited by nutrients,so it was speculated that it is more competitive than other species because of its higher absorption rate of nutrients,which leaded to its massive reproduction in the southern water.Our suggestions are as follows:in spring,it is necessary to guard against Noctiluca scintillans red tide in Xiaoshi Island near the urban area and its harm to sea cucumber culture.In summer,it is necessary to guard against toxic and harmful dinoflagellates in the north of Rongcheng,and pay more attention to food safety caused by toxins.In autumn,we should pay attention to the migration of common red tide algae such as Akashiwo sanguinea to the south with the current to prevent them from competing with Rongcheng kelp seedlings for nutrients.In addition,in autumn,we should pay attention to the harm of the outbreak of Eucampia zodiacus algae in the southern water to the cultivation of Wendeng laver,and further evaluate the impact of the outbreak of floating corner algae on the growth of oysters.