Patterns and Processes in Marine Microeukaryotic Community Biogeography from Xiamen Coastal Waters and Intertidal Sediments, Southeast China

Abstract

Microeukaryotes play key roles in the structure and functioning of marine ecosystems. Little is known about the relative importance of the processes that drive planktonic and benthic microeukaryotic biogeography in subtropical offshore areas. This study compares the microeukaryotic community compositions (MCCs) from offshore waters (n = 12) and intertidal sediments (n = 12) around Xiamen Island, southern China, using high-throughput sequencing of 18S rDNA. This work further quantifies the relative contributions of spatial and environmental variables on the distribution of marine MCCs (including total, dominant, rare and conditionally rare taxa). Our results showed that planktonic and benthic MCCs were significantly different, and the benthic richness (6627 OTUs) was much higher than that for plankton (4044 OTUs) with the same sequencing effort. Further, we found that benthic MCCs exhibited a significant distance-decay relationship, whereas the planktonic communities did not. After removing two unique sites (N2 and N3), however, 72% variation in planktonic community was explained well by stochastic processes. More importantly, both the environmental and spatial factors played significant roles in influencing the biogeography of total and dominant planktonic and benthic microeukaryotic communities, although their relative effects on these community variations were different. However, a high proportion of unexplained variation in the rare taxa (78.1-97.4%) and conditionally rare taxa (49.0-81.0%) indicated that more complex mechanisms may influence the assembly of the rare subcommunity. These results demonstrate that patterns and processes in marine microeukaryotic community assembly differ among the different habitats (coastal water vs. intertidal sediment) and different communities (total, dominant, rare and conditionally rare microeukaryotes), and provide novel insight on the microeukaryotic biogeography and ecological mechanisms in coastal waters and intertidal sediments at local scale.

Keywords: benthos; biogeography; community assembly; deterministic processes; neutral model; plankton; stochastic processes; variation partitioning analysis.

FIGURE 1

Sketch map of Xiamen island showing the 24 sampling sites in offshore sea water (dots) and sandy beach sediment (stars). A total of 24 samples including 12 surface seawater samples (<0.5 m depth) and 12 surface sediment samples (0–5 cm depth) were collected from Xiamen coastal waters and intertidal sandy beaches in late July 2013 and early September 2014, respectively. The map of Xiamen Island with sampling sites was constructed using ArcGIS 10.1.

FIGURE 2

Comparison of microeukaryotic community between planktonic and benthic taxa at supergroup and OTU levels. (A) Relative abundance of richness (OTU numbers) and abundance (sequence numbers) of planktonic microeukaryotic taxa compared with benthic microeukaryotic taxa. Unclassified eukaryotes (sequence similarity >80%). Values are means ± SE (n = 12); ^∗P <0.05 (Student’s t-test). (B) Venn diagrams showing the number and percentage of OTUs that are unique and shared between the microeukaryotic plankton and benthos. All, all taxa; AT, abundant taxa; CAT, conditionally abundant taxa; CRAT, conditionally rare and abundant taxa; RT, rare taxa; CRT, conditionally rare taxa.

FIGURE 3

Microeukaryotic community beta-diversity visualized using non-metric multidimensional scaling (NMDS) based on Bray–Curtis similarity. All, all taxa; AT, abundant taxa; CAT, conditionally abundant taxa; CRAT, conditionally rare and abundant taxa; RT, rare taxa; CRT, conditionally rare taxa.

FIGURE 4

Fit of the neutral model (NM) of community assembly. The predicted occurrence frequencies for plankton and benthos representing microeukaryotic communities from seawater and sediment, respectively. The solid blue lines indicate the best fit to the NM as in Sloan et al. (2006) and dashed blue lines represent 95% confidence intervals around the model prediction. OTUs that occur more or less frequently than predicted by the NM are shown in different colors. Nm indicates metacommunity size times immigration, R² indicates the fit to the NM. (A) 12 plankton communities; (B) 12 benthic communities; (C) 10 plankton communities (after removing sites N2 and N3).