No abstract

Ciliates (protozoa) are ubiquitous components of plankton community and play important roles in aquatic ecosystems in regards of their abundance, biomass, diversity and energy turnover. Based on the stratified samples collected from the northern Beibu Gulf in August 2011, species composition, abundance, biomass, diversity and spatial pattern of planktonic ciliates were studied. Furthermore the main environmental factors controlling ciliate communities were determined. A total of 101 species belonging to 44 genera and 7 orders (i.e., Oligotrichida, Haptorida, Euplotida, Sessilida, Pleurostomatida, Scuticociliatida and Tintinnida) were identified. The variation of ciliate communities was significant at horizontal level, but that was not at vertical level. Based on cluster analysis, ciliate communities were divided into three main groups. Redundancy analysis (RDA) revealed that Group A, existing in the waters with higher concentration of phosphorus and nitrogen, was dominated by Tintinnidium primitivum. Group B in the waters with lower temperature and chlorophyll-a concentration, was dominated by Leegaardiella ovalis. Group C, existing in the waters with higher temperature and chlorophyll-a concentration, was dominated by large Strombidium spp. and Mesodinium rubrum. Combining multiple analytic methods, our results strongly supported that phosphorus, nitrogen and chlorophyll-a were the most significant factors affecting the ciliate communities in the northern Beibu Gulf in summer. Concentration of phosphorus and nitrogen primarily influenced ciliate biomass, implying a potential impact of eutrophication on ciliate growth. The correlation with chlorophyll-a concentration, on one hand indicate the response of ciliates to the food availability, and on the other hand, the ciliates containing chloroplasts or endosymbionts may contribute greatly to the chlorophyll-a.

The genus Aurelia is one of the major contributors to jellyfish blooms in coastal waters, possibly due in part to hydroclimatic and anthropogenic causes, as well as their highly adaptive reproductive traits. Despite the wide plasticity of cnidarian life cycles, especially those recognized in certain Hydroza species, the known modifications of Aurelia life history were mostly restricted to its polyp stage. In this study, we document the formation of polyps directly from the ectoderm of degenerating juvenile medusae, cell masses from medusa tissue fragments, and subumbrella of living medusae. This is the first evidence for back-transformation of sexually mature medusae into polyps in Aurelia sp.1. The resulting reconstruction of the schematic life cycle of Aurelia reveals the underestimated potential of life cycle reversal in scyphozoan medusae, with possible implications for biological and ecological studies.

Surveys were conducted in four seasons in the eastern Beibu Gulf from July 2006 to November 2007, to determine the ichthyoplankton composition, abundance, as well as environmental factors impacted on their spatiotemporal distributions. The fish eggs and larvae were sorted from 303 zooplankton quantitative samples, in which at least 1 order, 60 families, 31 genera and 61 species of fish eggs and larvae were identified. The species number was highest in summer whereas lowest in winter. With the most abundant fish egg (the average density was 2.41 ind./m 3 ), spring was the main spawning season, while the greatest mean density of fish larva was 1.35 ind./m 3 in summer. In the whole year around, fish eggs had the trends to aggregate in the nearshore of Guangxi coast, fish larvae were more abundant in the northern water. Relationships between fish eggs and larvae abundance and environmental factors were analyzed by using the Yield-Density model. The spatiotemporal distribution of ichthyoplankton in eastern Beibu Gulf was closely related to the Chl a concentration, and the optimal temperature, salinity and Chl a were 19.4-21.7 • C, 31.8-33.1 and 1.5-4.8 mg/m 3 , respectively. Additionally, the distribution of fish larvae could be effected by ocean currents in summer and autumn.

The genus Clytia is distributed worldwide, but most accepted species in this genus have been examined either only at the hydroid or medusa stage. The challenge in identifying Clytia species reflects their complex life cycles and phenotypic plasticity. In this study, molecular and morphological investigations of Clytia specimens from the coastal waters of China revealed an as yet unreported species, designated C. xiamenensis sp. nov., that was considered as conspecific to two nearly cosmopolitan species, C. hemisphaerica and C. gracilis. DNA barcoding based on partial mitochondrial cytochrome c oxidase subunit I (COI) and large subunit ribosomal RNA gene (16S) confirmed the highly distinct lineage of C. xiamenensis sp. nov. These results were corroborated by the detailed observations of its mature medusae and its colonies, which showed that C. xiamenensis sp. nov. was morphologically distinct from other species of Clytia. Thus, based on our findings, the nearly cosmopolitan distribution attributed to some species of Clytia might rather be due to the misidentification, and it is necessary to elucidate their whole life cycle in order to establish the systematic validity of all species within the genus Clytia.