Ciliate Community Structures In Typical Subtropical Bays And Their Relationships With Environment

Ciliates are significant components of microplankton communities in the ocean and play a crucial role in microbial food webs. By virtue of their sensitive reaction to environmental changes, they have been considered as effective bioindicators of water quality and ecosystem. This study was carried out in the northern Beibu Gulf, South China Sea and Shenhu Bay in Fujian Province. The taxonomic composition as well as the spatial and temporal distribution of ciliates was characterized. The community structure was analyzed, and the main environmental factors that controlling the ciliate communities were determined. The main results are as follows:1. Based on the surface water samples collected in the northern Beibu Gulf in spring, a total of36species belonging to13genera and3orders (Oligotrichida, Haptorida and Tintinnida) were identified.In spring, the abundance of total ciliates ranged from555to5985ind. L-1. The abundance of aloricate ciliates ranged from555to5970ind. L-1, and tintinnid abundance ranged from0to285ind. L-1. High abundance of total ciliates and aloricate ciliates exhibited a patchy distribution pattern, with higher values in the following areas:the coastal waters of the border region of China and Vietnam, the area west of Qiongzhou Strait, and the waters near Tieshan Harbor. The higher abundance of tintinnids concentrated in the southwest of the study area and the area west of Qiongzhou Strait.2. Based on the stratified samples collected in summer,101species belonging to42genera and7orders (Oligotrichida, Haptorida, Euplotida. Peritrichida, Pleurostomatida, Scuticociliatida, Tintinnida) were recorded.In summer, the ciliate abundance was higher in the nearshore waters than in the offshore waters, and the higher values were recorded in the coastal region of Guangxi and the area west of Leizhou Peninsula, especially adjacent to Tieshan Harbor. The biomass decreased westwards from the west coast of Leizhou Peninsula. The distribution trend of species number was not consistent in different layers. The Shannon-Wiener diversity, contrary to the trend of abundance, was obviously lower in the nearshore waters than in the offshore waters. The abundance of total ciliates ranged from540to10950ind. L-1, and their biomass ranged from0.45to30.53μgC. L-1.The vertical distributions of ciliate abundance and biomass were consistent in the northern Beibu Gulf. The aggregated areas were recorded at a depth of about10m in the nearshore waters, while descended to about30m in the offshore waters. The vertical distributions of species number and diversity were very similar. There was a significant variation in spatial distribution of ciliate communities at horizontal level, whereas there was no significant variation at vertical level.3. The main environmental factors influencing the spatial variation of ciliate communities in the northern Beibu Gulf differed between spring and summer. In spring, the level of nitrogen and phosphorus nutrients had the most significant influence on ciliate communities. As the level of nitrogen and phosphorus nutrients increased, the proportion of oligotrichs in ciliate communities declined, whilst that of Mesodinium spp. increased. In summer, phosphorus, nitrogen and chlorophyll-a concentration were the most significant factors controlling ciliate communities. The chlorophyll-a concentration significantly influenced abundance, biomass and species number of ciliates, while the concentration of phosphorus and nitrogen nutrients primarily influenced ciliate biomass.4. Based on the study of large tintinnids (>76μm) collected from Shenhu Bay in spring, summer and autumn, a total of36species representing10genera were identified. In spring,21species belonging to6genera were recorded. The mean abundance and biomass were2063.98±440.56ind. m-3and109.30±24.95μgC. m-3, respectively. In summer,16species belonging to7genera were recorded. The mean abundance and biomass were6704.70±1108.75ind. m"3and219.28±38.02μgC. m-3, respectively. In autumn,16species belonging to5genera were recorded. The mean abundance and biomass were352.23±44.48ind. m"3and2.38±0.46μgC. m-3, respectively.The taxonomic composition, abundance, biomass of tintinnids and their spatial pattern were characterized by a clear seasonality. The tintinnids were most diverse in spring, however their abundance and biomass peaked in summer. The seasonal variation of tintinnid communities was more significant than the spatial variation. In addition, an obvious seasonal succession of the dominant species was exhibited. Their lorica size as well as the abundance and biomass decreased obviously in autumn.The main environmental factors controlling the spatial pattern of tintinnid communities were different in each season in Shenhu Bay. In general, temperature, salinity and levels of nutrients and pollutants had the greatest effects on the seasonal and spatial variation of tintinnid communities.5. The abundance of total ciliates in the northern Beibu Gulf in this survey was within the ranges reported in the different seas surrounding in China, however the abundance of tintinnids was relatively low in the surface water in spring. The large tintinnids was less abundant in Shenhu Bay in autumn than in other seas surrounding in China.