text: **Supplementary Materials:**The following are available online at http://www.mdpi.com/1660-4601/17/3/1062/s1. 
  
  **Author Contributions:**W.S. designed the study, collected the data, conducted the analysis, and wrote the article. 
  H.F. oﬀered suggestions to the part of temporal analysis. P.W. contributed to the hashtag co-occurrence part. C.C. 
  helped with the design of the study. J.X. contributed to the framing of the article and helped with the revision. 
  All authors have read and agreed to the published version of the manuscript. 
  
  **Funding:**This work was supported in part by the National Key R&D Program of China (Grant No. 
  2017YFA0604500), by the National Natural Science Foundation of China (Grant No. 51761135015, 71772142 and 
  U1839206), by the National Social Science Foundation of China (Grant No.18ZDA307), by the Center for High 
  Performance Computing and System Simulation, and by the Pilot National Laboratory for Marine Science and 
  Technology (Qingdao). 
  
  **Conﬂicts of Interest:**The authors declare no conﬂict of interest. 