Critical factors driving spatiotemporal variability in the phytoplankton community structure of the coral habitat in Dongshan Bay, China

Abstract

This study investigated the spatiotemporal distribution of the phytoplankton in the coral habitat of Dongshan Bay (China), along with critical factors affecting the distribution, during June, August, and December 2022. Phytoplankton abundance in Dongshan Bay exhibited considerably temporal variation, peaking in June 2022, gradually decreasing thereafter, and reaching its lowest point in December 2022. The abundance of bottom-layer phytoplankton consistently exceeded that of the surface layer throughout all seasons. The average phytoplankton abundance in the coral habitat of Dongshan Bay was lower than that in non-coral habitat areas. Fluctuations in the Zhangjiang River and coastal upwelling influenced the diversity and community structure of the phytoplankton. Critical factors causing spatiotemporal variability in phytoplankton community structure included nutrient concentrations and seawater temperature. Nutrients played key roles in influencing various phytoplankton groups. Dominant diatom species, such as Thalassionema nitzschioides and Thalassiosira diporocyclus, were positively correlated with ammonia nitrogen, seawater salinity, coral cover, and the number of coral species present. In winter, Calanus sinicus exhibited a negative correlation with harmful algal bloom species. Additionally, it was found that both in the coral habitat and surrounding open sea, currents, nutrients, and zooplankton may play crucial roles in determining the spatiotemporal variability in the phytoplankton community structure.

Keywords: community structure; coral habitat; current; nutrient; phytoplankton; spatiotemporal variability.

Figure 1

Geographic location of the investigated stations in Dongshan Bay, China (black sampling sites are not included in August; blue sampling sites are non-coral habitat stations; red sampling sites are coral habitat stations). In the right figure, the solid black arrow indicates the Zhangjiang River Diluted Water (ZDW); the dotted black arrow indicates Zhe-Min Coastal Current (ZMCC).

Figure 2

Spatial variations of phytoplankton species number (A) June; (B) August; (C) December.

Figure 3

Temporal variation of phytoplankton species number in Dongshan Bay.

Figure 4

Dendrogram of cluster analysis of phytoplankton assemblage collected in Dongshan Bay.

Figure 5

Ecological indices of phytoplankton in Dongshan Bay.

Figure 6

Spatiotemporal distribution of phytoplankton abundance in Dongshan Bay (A) June; (B) August; (C) Decmber.

Figure 7

Circos plot of temporal variation of phytoplankton abundance in Dongshan Bay.

Figure 8

Spatiotemporal variability of chemical factors in Dongshan Bay (The left vertical axis represents the values of the bar chart, while the right vertical axis represents the values of the line chart.).

Figure 9

Spatiotemporal variability of coral community in Dongshan Bay (The left vertical axis represents the values of the bar chart, while the right vertical axis represents the values of the line chart.).

Figure 10

Principal Component Analysis (PCA) biplot analysis for phytoplankton abundance with physico-chemical parameters in Dongshan Bay. (NH₄, ammonia nitrogen; DIN, dissolved inorganic nitrogen; PO₄, phosphate; SiO₃, silicate; NO₃, nitrate; NO₂, nitrite; DO, dissolved oxygen; CHN, Coral Habitat Area; NCHA, Non-Coral Habitat Area).

Figure 11

Redundancy analysis (RDA) for phytoplankton abundance with associated chemical parameters in Dongshan Bay (NH₄: ammonia nitrogen, DIN: dissolved inorganic nitrogen, PO₄: phosphate SiO₃: silicate; NO₃: nitrate; NO₂: nitrite; DO: dissolved oxygen; the yellow circle represents June; dark red circle represents August; gray circle represents December).

Figure 12

Redundancy analysis (RDA) for phytoplankton abundance with biotic factors, in Dongshan Bay.