Community Structure of Diatoms and Its Water Factors in Gaogongdao Island China Offshore Area

Phytoplankton is the primary producer of the ocean. The variation of its variety and quantity will control the secondary productivity as well as the biomass of fish and other marine animal resources. Diatoms play an important role in the food web of the sea. Though many studies on the phytoplankton of the Yellow Sea are known, most of them were large scale studies covering the whole Yellow Sea. Few studies of diatoms were carried out near Gaogong Island area. In August 2009, the species composition, quantitative distribution, dominant species and community structural characteristics of diatoms were studied at 14 stations near Gaogong Island area. 63 species of 25 genera of Bacillariophyceae were identified in the studied waters. The abundance of diatoms varied from 0.396×10⁵ ind/L to 2.994×10⁵ ind/L with an average of 1.698×10⁵ ind/L. In this investigation, it was found that Guinardia striata had the most contribution to the main abundance, and next were Eucampia zodiacus. They were the main groups of the phytoplankton. There were 4 species with dominance>;0.02 in the zone. among which Cuinardia striata (Stolterfoth)Hasle,Eucampia,zodiacus Ehren- berg, Chaetoceros pseudocurvisetus Mangin, Chaetoceros tortissi-mus Gran were the main dominant species, whose the dominance index were 0.741,0.221,0.151 and 0.111 respectively. The indexes amplitude varied greatly (the species from 15 to 34, the richness 0.833-1.814, the diversity index 1.694-3.135, the evenness index 0.429-0.680) , which indicates the instability of community structure. The mean diversity index of diatoms was 2.654, the mean richness index was 1.432, the mean evenness index was 0.569. The analysis of correlations showed that water temperature and the evenness index and the diversity index were extremely significantly correlated (P<;0.05) (correlation coefficient: 0.676 and 0.684, respectively; P<;0.05). We observed a significant relatio- ship between water temperature and ammonia nitrogen content, silicate content, and nitrite content correlation coefficients: 0.689, 0.749 (P<;0.01), and 0.572 (P<;0.05), respectively. The number of the species and nitrate content were significantly correlated (P<;0.05) (correlation coefficient: 0.550). Eucampia zodiacus and the depth of water were negative significantly correlated (P<;0.05) (correlation coefficient: -0.542). Skeletonema costatum and Suspended solids content and Phosphate content were significantly correlated (correlation coefficient: 0.590 and 0.571, respectively; P<;0.01 and P<;0.05).