Benthic ciliate and meiofaunal communities in two contrasting habitats of an intertidal estuarine wetland

Annual variations in benthic meiofaunal and ciliated protozoan communities were investigated using monthly samplings from June 2006 to May 2007 in two habitats characterized by different vegetal coverage in an estuarine intertidal wetland of Qingdao Jiaozhou Bay, China. The sediment composition was stable at each site: sediments densely covered with seagrass (Suaeda glauca) in the lower estuarine site (Station S) were finer, with higher content of organic matter, phaeopigments and water than sediments at the upper estuarine site (Station S-P) which was unvegetated other than for patches of S. glauca and common reed (Phragmites australis). Chlorophyll a exhibited a similar distribution in the two habitats. A total of 14 meiofaunal groups, and 249 species of ciliates belonging to 37 genera, 28 families and 16 orders, were isolated from the two sites. Univariate and multivariate measures of the communities were significantly different between the two habitats. There were higher abundances of ciliates and meiofauna, and a greater diversity of ciliates, at Station S than Station S-P (223 vs. 61 species). Herbivorous ciliates were numerically predominant in ciliate communities at both sites. The representative ciliates at Station S-P belonged to the Cyrtophorida and appeared to be a reduced subset of the assemblage at Station S, which was characterized by members of the Prostomatida, Cyrtophorida, Hypotrichida and Scuticociliatida. More than 96% of the total meiofauna were nematodes, accounting for 93% of the differences in the abundance compositions of the meiofaunal communities between habitats. The average individual weights of nematodes were nearly 3 times greater at Station S than Station S-P, indicating a distinctive species composition at each site. Temperature, salinity and food availability were key factors that regulated the ciliate and meiofaunal community structure. Nematodes were the dominant group in terms of the combined abundance, biomass and benthic metabolism of ciliates and meiofauna. With respect to the dominance of herbivorous ciliates and epistrate-feeder nematodes in seagrass sediment, predator–prey relationships and competition for food resources between nematodes and ciliates are likely to be important factors in controlling the abundances of these groups.

► Benthic ciliate and meiofauna communities were investigated in an estuarine wetland.
► Ciliates in unvegetated sediments was a reduced subset of those at seagrass sediments.
► Nematodes dominated in terms of the combined community of ciliates and meiofauna.
► Regulators for ciliate and meiofauna were temperature, salinity and food availability.
► Competition for resources between nematodes and ciliates could be key relationship.