Potential impacts of anthropogenic nutrient enrichment on coral reefs in the South China Sea: evidence from nutrient and chlorophyll a levels in seawater

2019 ◽  
Vol 21 (10) ◽  
pp. 1745-1753
Author(s):  
Jing Guo ◽  
Kefu Yu ◽  
Yinghui Wang ◽  
Ruijie Zhang ◽  
Xueyong Huang ◽  
...  
Keyword(s):  
Coral Reef ◽  
South China Sea ◽  
Coral Reefs ◽  
Chlorophyll A ◽  
South China ◽  
Nutrient Enrichment ◽  
The South China Sea ◽  
Macroalgal Blooms ◽  
Reef Degradation ◽  
Coral Reef Degradation

Anthropogenic nutrient enrichment caused macroalgal blooms and further resulted in coral reef degradation in coastal and some remote reef areas of the SCS.

scholarly journals Diazotroph diversity associated with scleractinian corals and its relationships with environmental variables in the South China Sea

2019 ◽  
Author(s):  
Jiayuan Liang ◽  
Kefu Yu ◽  
Yinghui Wang ◽  
Xueyong Huang ◽  
Wen Huang ◽  
...  
Keyword(s):  
Coral Reef ◽  
South China Sea ◽  
Coral Reefs ◽  
South China ◽  
Human Activities ◽  
Environmental Variables ◽  
The South China Sea ◽  
The South ◽  
Fringing Reef ◽  
China Sea

Abstract Background: Coral reef ecosystems cannot operate normally without an effective nitrogen cycle. For oligotrophic coral reef areas, coral-associated diazotrophs are indispensable participants in the nitrogen cycle. How coral-associated diazotrophs will change in order to adapt to environmental changes resulting from global warming and human activities is a topic of concern for researchers. To this end, 68 colonies of scleractinian coral were collected from 6 coral reefs areas with different environmental variables in the South China Sea to investigate the composition of associated diazotrophs based on nifH gene amplification using high-throughput sequencing. The six coral reefs can be clearly divided into two types (fringing reefs and island reefs), are affected by varying degrees of human activities and are located at different latitudes from 9°20′06′′N to 22°34′55′′N with different seawater temperatures. Results: Alpha- and beta-diversity analyses showed that the distribution of diazotrophs among coral reefs exhibited greater geographical fluctuations than interspecific fluctuations. The predominant bacterial phyla included Proteobacteria, Chlorobi, Cyanobacteria, and two unclassified phyla. Chlorobi exhibited an abundance of 47–96% in coral samples from the high-latitude Daya Bay fringing reef affected by eutrophication. Unclassified bacteria II, with an abundance of 28–87%, was found in all coral samples from the midlatitude Luhuitou fringing reef affected by eutrophication. However, unclassified bacteria I and Proteobacteria dominated (> 80% abundance) in most of the coral samples from the Weizhou Island fringing reef, which is far from land, and three island reefs (Huangyan Island, Xinyi Reef, and Sanjiao Reef) at relatively low latitudes. At the genus level, some core diazotrophs were found in different coral sample groups. In addition, the correlation analysis with various environmental variables revealed that the variables correlated positively or negatively with different diazotrophic genera. Conclusions: We found that coral-associated diazotrophs were common among coral individuals. The presence of these diazotrophs was not affected by the external environment, but their population abundances were closely related to the different environmental variables. These results provide insights into the ecological characteristics of coral-associated diazotrophs and their relationships with critical environmental variables in the South China Sea.

scholarly journals Spatiotemporal Variability of Surface Phytoplankton Carbon and Carbon-to-Chlorophyll a Ratio in the South China Sea Based on Satellite Data

2020 ◽  
Vol 13 (1) ◽  
pp. 30
Author(s):  
Wenlong Xu ◽  
Guifen Wang ◽  
Long Jiang ◽  
Xuhua Cheng ◽  
Wen Zhou ◽  
...  
Keyword(s):  
South China Sea ◽  
Chlorophyll A ◽  
South China ◽  
Satellite Data ◽  
Phytoplankton Biomass ◽  
The South China Sea ◽  
Spatiotemporal Variability ◽  
The South ◽  
Chl A ◽  
China Sea

The spatiotemporal variability of phytoplankton biomass has been widely studied because of its importance in biogeochemical cycles. Chlorophyll a (Chl-a)—an essential pigment present in photoautotrophic organisms—is widely used as an indicator for oceanic phytoplankton biomass because it could be easily measured with calibrated optical sensors. However, the intracellular Chl-a content varies with light, nutrient levels, and temperature and could misrepresent phytoplankton biomass. In this study, we estimated the concentration of phytoplankton carbon—a more suitable indicator for phytoplankton biomass—using a regionally adjusted bio-optical algorithm with satellite data in the South China Sea (SCS). Phytoplankton carbon and the carbon-to-Chl-a ratio (θ) exhibited considerable variability spatially and seasonally. Generally, phytoplankton carbon in the northern SCS was higher than that in the western and central parts. The regional monthly mean phytoplankton carbon in the northern SCS showed a prominent peak during December and January. A similar pattern was shown in the central part of SCS, but its peak was weaker. Besides the winter peak, the western part of SCS had a secondary maximum of phytoplankton carbon during summer. θ exhibited significant seasonal variability in the northern SCS, but a relatively weak seasonal change in the western and central parts. θ had a peak in September and a trough in January in the northern and central parts of SCS, whereas in the western SCS the minimum and maximum θ was found in August and during October–April of the following year, respectively. Overall, θ ranged from 26.06 to 123.99 in the SCS, which implies that the carbon content could vary up to four times given a specific Chl-a value. The variations in θ were found to be related to changing phytoplankton community composition, as well as dynamic phytoplankton physiological activities in response to environmental influences; which also exhibit much spatial differences in the SCS. Our results imply that the spatiotemporal variability of θ should be considered, rather than simply used a single value when converting Chl-a to phytoplankton carbon biomass in the SCS, especially, when verifying the simulation results of biogeochemical models.

scholarly journals The variability of chlorophyll-a and its relationship with dynamic factors in the basin of the South China Sea

2019 ◽  
Vol 200 ◽  
pp. 103230 ◽  
Author(s):  
Yi Yu ◽  
Xiaogang Xing ◽  
Hailong Liu ◽  
Yeping Yuan ◽  
Yuntao Wang ◽  
...  
Keyword(s):  
South China Sea ◽  
Chlorophyll A ◽  
South China ◽  
The South China Sea ◽  
The South ◽  
China Sea ◽  
Dynamic Factors

scholarly journals Coral reef ecosystems in the South China Sea as a source of atmospheric CO2 in summer

2011 ◽  
Vol 56 (7) ◽  
pp. 676-684 ◽  
Author(s):  
HongQiang Yan ◽  
KeFu Yu ◽  
Qi Shi ◽  
YeHui Tan ◽  
HuiLing Zhang ◽  
...  
Keyword(s):  
Coral Reef ◽  
South China Sea ◽  
South China ◽  
The South China Sea ◽  
Atmospheric Co2 ◽  
The South ◽  
China Sea ◽  
Coral Reef Ecosystems

scholarly journals The Effect of the ENSO on the Variability of SST and Chlorophyll-a in the South China Sea

2019 ◽  
Vol 246 ◽  
pp. 012027 ◽  
Author(s):  
Siti Maisyarah ◽  
Anindya Wirasatriya ◽  
Jarot Marwoto ◽  
Petrus Subardjo ◽  
Indra B Prasetyawan
Keyword(s):  
South China Sea ◽  
Chlorophyll A ◽  
South China ◽  
The South China Sea ◽  
The South ◽  
China Sea
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