The algae community in taxon Haptophyceae at the early bloom stage of Phaeocystis globosa in Northern Beibu Gulf in winter

Phaeocystis globosa (Order Phaeocystales, family Phaeocystaceae) caused significant impact on aquaculture farming, global climate change and industry. Since the year 2010, intensive red tides of P. globosa began to appear in Beibu Gulf, where previously free of harmful algal blooms, and posed great threats to the cooling systems of a nuclear power plant in 2014 and 2015. In order to discover the bloom mechanism, the community structure of marine microalgae, with a focus on Haptophyceae taxa, in winter in the northern Beibu Gulf near the Qinzhou Bay, Sanniang Bay (SNB) and Dafenjiang River Estuary (DRE), were explored via 18S ribosomal DNA analysis of the V4 region using the Illumina-Based Sequencing platform. The correlation between the relative abundance of five kinds of Haptophyceae algae and environmental factors of seawater were analyzed. The most abundant Haptophyceae-related OTU in terms of number of reads was identified as Phaeocystis and Chrysochromulina. The abundance for other Haptophyceae class was relatively low, such as Haptolina, Prymnesium and Isochrysis. Phaeocystis was present in all samples sites except S6, S11, S12, S14 and S15, and particularly abundant at S8, nearly 29 times more than the second most abundant site. Most notably, the results showed that Phaeocystis displayed highly positive linear correlation with the concentration of NO3--N (Pearson r=0.856, p<0.01). Linear regression analysis indicated that Phaeocystis was significantly linearly related to the NO3--N (R2=0.732; Y=-0.005 + 0.410*X, Y is the relative abundance of P.globosa, X is the concentration of NO3--N; F=38.227, P<0.05) and NO3--N has a significant positive effect on P.globosa (regression coefficient is 0.410, P=0.000). Moreover, the relative abundance of Phaeocystis was significant related to temperature of sea water (Pearson r=-0.882,p<0.01). Water temperature can explain the 77.8% change reason for the P.globosa (R2=0.778), and has a significant effect on P. globosa (Y=0.169-0.009*X, F=49.031,P<0.05), and the regression coefficient is -0.009 (P=0.000) which indicated a significant negative impact relationship between them. Our high throughput sequencing (HTS) based research illustrated how the P. globosa bloom generated and its relationship with NO3--N and temperature of sea water in northern Beibu Gulf for the first time, and bringing hope for solving this big problem.