Progress in studies on the diversity and distribution of planktonic ciliates (Protista, Ciliophora) in the South China Sea

Abstract

As an important component of microzooplankton, ciliates play a key role in matter cycling and energy flow in marine planktonic ecosystems. Studies of planktonic ciliate have been extensive in the South China Sea (SCS) over the last 20 years. Here, we summarize the recent progress on the diversity and distribution of this group in the SCS. This includes that in: (1) the waters covering the intertidal zone of the northern SCS, most studies have focused on taxonomy, with 71 species collected, identified, and described (with ~ 40% new species); (2) neritic waters distribution patterns have been examined at a regional scale, with ciliates displaying significant spatial variations and seasonal dynamics; (3) in oceanic waters, there has been a focus on ciliate distribution in north, centre, and south regions, where mesoscale physical processes play roles in controlling distributions, and noticeable vertical variations occur. More generally, some studies examine the influences of environment variables on ciliates, and indicate that chlorophyll a concentration is commonly positively correlated with ciliates abundance. In addition, some significant findings are summarized, the limitations of past studies are considered, and recommendations are made for future work on planktonic ciliates in SCS.

Distribution Patterns of Ciliate Diversity in the South China Sea

“…This was in accordance with some previous studies that found alpha diversity of planktonic ciliates decreased with increasing distance from shore (Doherty et al, 2010;Tamura et al, 2011). The high ciliate diversity in intertidal water may be explained by the diverse habitats and heterogeneous environmental characters there, which thus supplies a wide range of niches for ciliates (Liu et al, 2021). Second, the composition patterns of ciliates in intertidal water differs strikingly from other areas in terms of taxonomy, motility and feeding habits (Figures 1A,C,D).…”

“…Data were compiled from different sources include one monograph (Hu et al, 2019) and all papers on marine ciliate biodiversity in SCS based on morphological identification from 1991 to 2018 (for the list of papers, see Liu et al, 2021). In total 592 species from 30 investigations were included in the data set (see Supplementary Table S1 in Supplement for a complete list).…”

“…Considering spatial environmental variation, we firstly analyzed the large-scale patterns of ciliate community composition based on three geographical area groupings, i.e., the intertidal area (waters covering the area between the low and high tides), the neritic area (beyond the intertidal zone and over the continental shelf), and the oceanic area (from the shelf break to the deep sea) (Liu et al, 2021). Subsequently, in each area, the distribution variations of ciliates on a regional scale were analyzed based on 3-4 subarea groupings (Supplementary Figure S1).…”

“…For instance, 789 planktonic ciliates have been found in the Baltic Sea (Mironova et al, 2009) and 620 in the Caspian (Alekperov, 2007). Apparently, the diversity of ciliates in the SCS is still not well studied, especially in the wide oceanic areas such as the central and southern SCS where the area accounts for 2/3 of SCS but only four investigations have been conducted (Liu et al, 2021). For the taxonomic composition of ciliates, species of the subclasses Choreotrichia and Oligotrichia represent the dominant group in the SCS (Supplementary Figure S2).…”

Taxonomy and SSU rDNA-Based Phylogeny of Two Heterotrich Ciliates (Ciliophora, Heterotrichea) Collected From Subtropical Wetlands of China, Including the Description of a New Species, Linostomella pseudovorticella n. sp.

“…Ciliated protists (ciliates) are a morphologically diverse and highly specialized group of microbial eukaryotes that constitute an important component of the microbial food web (Azam et al, 1983;Dolan et al, 2012;Miao et al, 2020;Zhao et al, 2020;Liu et al, 2021). Members of the ciliate class Heterotrichea Stein, 1859 are characterized by their typically large body, prominent oral apparatus, and somatic kineties composed of dikinetids with postciliodesmata (Lynn, 2008;Song et al, 2009;Shazib et al, 2014;Hu et al, 2019).…”