关键词: 养马岛扇贝养殖区, 浮游植物, 环境因子, 典范对应分析, scallop culture areas of Yangma Island, phytoplankton, environmental factors, canonical correspondence analysis

Abstract: The scallop culture area of Yangma Island is located in Yantai Shiliwan Bay. The latter is an ear-shaped semi-closed bay. There are many rivers such as Xin'an River along the coast. It is an important shallow sea culture area in the North Yellow Sea. As an important primary producer in the marine ecosystem, phytoplankton has the characteristics of short life cycle and sensitivity to environmental changes, and is used as an important indicator organism for evaluating the nutrient grade of water bodies. Its community structure can better reflect nutritional status of aquatic ecosystems. While planktonic algae have the ability to absorb nitrogen and phosphorus, which can purify water bodies and help scallops grow. However, when a large amount of land-source input causes the concentration of nitrogen and phosphorus to be too high, the overgrowth of phytoplankton will occur, which may cause red tide. Wang Wenjun analyzed the outbreak of marine card shield algae in the Sishili Bay in 2014, which proved that excessive nitrogen nutrient salt is a key factor in the occurrence of this red tide. In addition, phytoplankton is also an important bait for scallops. Zhang Lihong studied the feeding habits of scallops in Sanggou Bay and found that the algae that scallops mainly feed on are diatoms and dinoflagellates. Wang et al surveyed Yantai Shiliwan Bay showed that the dominant species of planktonic algae were mainly diatom-diatomaceous-branched algae in summer, and the main season was mainly diatom, which was consistent with the feeding habit of cultured scallops. Therefore, the detection of the composition and density of phytoplankton in the cultured sea area is of great significance for the monitoring of the ecological environment of the sea area and the rational culture and breeding of scallops. In this papper, the investigation of seven voyages were carried out in three scallop culture areas of Yangma Island from May to November in 2018. The composition, density, Shannon-Winner diversity index, Pielou evenness index, Margalef richness index and Mc-Naughton dominance index of phytoplankton community structure were analyzed, and the influence of environmental factors on phytoplankton dominant species in Yangma Island scallop culture area was discussed by canonical correspondence analysis ( CCA ). The results showed that there were 60 species of planktonic algae in 34 genera of 5 phyla detected in this area, mainly diatom and dinoflagellate, accounting for 73.33% and 13.33% respectively. The density of phytoplankton ranges from 1.49× 104 to 124.92× 104 cells /L, with the highest density occurring in June and the lowest density occurring in November. Dominant species include Pseudonitzschia pungens, Isochrysis sp., Cryptococcus sp., Guinardia delicatula, Chaetoceros compressus and Leptocylindraceae danicus etc. The diversity index, evenness index and richness index of phytoplankton varied from 0.51 to 3.62, 0.14 to 1.00 and 1.08 to 4.12 respectively. CCA analysis shows that inorganic nitrogen, Inorganic phosphorus, salinity, pH and temperature are the main factors affecting phytoplankton in the sea area, and the response mechanisms of various phytoplankton to environmental factors are different. In general, the phytoplankton in scallop culture area of Yangma Island is distributed reasonably and has stable structure, which is suitable for scallop culture.