Abstract:The phytoplankton community structure in the coastal aquaculture area of Rongcheng was analyzed based on the results of four surveys during 2016. The influence of environmental factors on the phytoplankton community in the Rongcheng coastal aquaculture area was discussed using canonical correlation analysis. The results identified a total of 66 species that belong to 29 genera of 3 phyla. The dominant species of phytoplankton include Skeletonema costatum, Melosira sulcate, Asterionellopsis glacalis, Chaetoceros tortissimus, Nitzschia pungens, and Chaetoceros lorenzianus with seasonal succession. In the spring A. glacalis increased quickly in Rongcheng Bay to make it the most important dominant species of this season, but not in Sanggou Bay, when compared with the results of previous studies. The abundance of phytoplankton varied from 16.9×104 to 251.7×104 cells/m3 over the 4 seasons, the average density of whole year was 119.3×104 cells/m3, which was the highest in summer and the lowest in autumn. The Shannon-Wiener diversity index and Pielou’s index range from 1.60 to 2.13 and 0.40 to 0.60, respectively, and the diversity of phytoplankton was the highest in the summer, and the mode of the phytoplankton structure changed with the seasons, but the levels of phytoplankton remained normal all year round. Canonical correlation analysis showed that the most important factors affecting phytoplankton community structure are dissolved oxygen, silicate, NH+4, sea surface temperature and pH. These may promote or inhibit the growth of specific species and cause the rise of dominant species. Large-scale kelp farming in the area changed the amount of nutritional salt, high density shellfish farming consumed the natural enemies of phytoplankton, and shellfish excretion also changed the composition of nutritional salts in the coastal waters; therefore, local aquaculture in the Rongcheng coastal waters may be an important factor in the pattern of phytoplankton community structure in addition to the influences of seasonal changes.
