Spatial and Intergeneric Variation in Physiological Indicators of Corals in the South China Sea: Insights Into Their Current State and Their Adaptability to Environmental Stress

Abstract

It is well known that coral thermal bleaching is mainly caused by abnormally high temperatures, but the spatial/intergeneric variation in coral‐algal symbiosis and its linkage to coral bleaching susceptibility is not well understood. In this study, 654 coral samples were collected from six coral reef regions (CRRs) in the South China Sea (SCS), between the Nansha Islands (~10°N) and Daya Bay (22°50′N). They were analyzed to explore how geographical/environmental variation affects coral bleaching susceptibility. The results showed significant spatial and intergeneric variation in zooxanthellae density, Chl a content, and tissue biomass. Massive corals generally showed higher values than branching corals for all three parameters across CRRs. Spatial analysis showed that these parameters were lowest in the Nansha Islands and highest in Daya Bay, indicating increases with latitude. Several factors may have accounted for this trend, with the most important being sea surface temperature and nutrients. Additionally, we observed a relationship between physiological parameters and bleaching susceptibility, which was that branching corals had greater bleaching susceptibility than massive corals. Coral community composition and live coral cover data showing increasing dominance of massive corals in the SCS support the above inference. Relatively high‐latitude areas have been proposed as potential refuges for corals under continued global warming and the physiological parameters in the present study seem to support this. However, in spite of the aforementioned results, the smallest live coral cover was found in the northern CRRs. This suggests that this refuge function is currently compromised, mainly due to increasing destructive anthropogenic actions.

Intergeneric Differences in Trophic Status of Scleractinian Corals From Weizhou Island, Northern South China Sea: Implication for Their Different Environmental Stress Tolerance

“…That is to say, higher ZD may be lead to higher reactive oxygen species production under high‐temperature condition and then exacerbate climate‐change‐induced coral bleaching (Cunning & Baker, 2013). Nevertheless, the intergeneric variation pattern of ZD in our study is consistent with the results of previous studies in field conditions in the SCS that ZD of relatively stress‐tolerant massive corals are significantly higher than that of relatively vulnerable plating and branching corals (Li et al, a, ; Qin et al, ; Xu et al, ).…”

Significant Changes in Microbial Communities Associated With Reef Corals in the Southern South China Sea During the 2015/2016 Global‐Scale Coral Bleaching Event

“…In the Nansha Islands (i.e., the Spratly Islands, southern South China Sea (SCS)), coral bleaching events, such as GCBEs, are one of the main threats to coral health, and lead to coral reef degradation and macroalgae occupation (e.g., Li et al, 2011;Yu et al, 2006). In situ observation during an investigation in June 2015 found that corals were in a healthy state such that almost no bleaching corals were found (e.g., Qin et al, 2019). In June 2016, the global El Niño event resulted in high SST anomalies such that corals suffered from high thermal stress.…”

Diazotroph Diversity Associated With Scleractinian Corals and Its Relationships With Environmental Variables in the South China Sea

“…In the South China Sea, coral reefs at low latitudes are also often subjected to unusually high temperatures. Statistics show that the Nansha Islands (where XyR and SjR are located) had annual maximum temperatures between 30 and 31 • C from 1985 to 2015 (Qin et al, 2019). The coral reefs located in high-latitude regions (e.g., Lht and DyB) are affected by human activities all year, resulting in serious eutrophication of the surrounding seawater.…”

“…The coral reefs located in high-latitude regions (e.g., Lht and DyB) are affected by human activities all year, resulting in serious eutrophication of the surrounding seawater. The live coral cover rapidly decreased from greater than 60% to less than 20% from 1984 to 2015 (Zhao et al, 2012;Qin et al, 2019). Diazotrophs are essential components of coral holobionts, which are involved in the nitrogen cycle (Piniak et al, 2003;Olson et al, 2009) and are important for energy supply (Hamilton et al, 2016).…”