TROPICAL GEOGRAPHY ›› 2016, Vol. 36 ›› Issue (6): 915-922.doi: 10.13284/j.cnki.rddl.002900

Previous Articles     Next Articles

Seasonal Responses of Symbiodinium in Stress-tolerant Porites lutea to Environmental Factors on Fringing Reefs of the Hainan Island

XU Lijia 1,3 ,YU Kefu 1,2 ,LI Shu 1   

  1. (1.Key Laboratory of Marginal Sea Geology,South China Sea Institute of Oceanology,Chinese Academy of Sciences,Guangzhou 510301,China;2.a.Coral Reef Research Center of China;b.School of Marine Sciences,Guangxi University,Nanning 530004,China;3.University of Chinese Academy of Sciences,Beijing 100049,China)
  • Received:2016-10-12 Online:2016-11-05 Published:2016-11-05


Due to global warming and increase in human activities, coral reefs worldwide have experienced severe declines recently,and scientific studies on their important causes keep on increasing. In this study, 194 samples of stress-tolerant Porites lutea were collected seasonally between October 2013 and August 2014 at fringing reefs in Sanya and Wenchang, Hainan Island, northern South China Sea (SCS), and their algal symbiont density and effective photochemical efficiency (Φ PSII ) were measured. The results indicated that both the Symbiodinium density and Φ PSII of P. lutea were subject to significant seasonal and spatial variations (Scheffe test,p<0.05). Seasonally, the mean Symbiodinium density in P. lutea varied from (2.23 ± 0.18) × 10 6 cells/cm 2 to (6.08 ± 0.36) × 10 6 cells/cm 2 , with the lowest density occurring in winter but a higher value in summer; the mean Φ PSII of Symbiodinium in P. lutea varied from (0.599 ± 0.01) to (0.717 ± 0.002) during seasons, with a higher Φ PSII in winter yet a lower value in spring and summer. Spatially, the mean Symbiodinium densities in P. lutea at the two reefs were (4.54 ± 0.33) × 10 6 cells/cm 2 (Wenchang, 1-2 m depth), (4.65 ± 0.33) × 10 6 cells/cm 2 (Sanya, 1-2 m depth), and (3.75 ± 0.29) × 10 6 cells/cm 2 (Sanya, 4-6 m depth). Although there were not significant differences between Wenchang and Sanya areas, the mean Symbiodinium densities of corals within 1-2 m depth were higher when compared to corals within 4-6 m depth. The mean Φ PSII of Symbiodinium in P. lutea at the two reefs were (0.625 ± 0.009) (Wenchang, 1-2 m depth), (0.680 ± 0.005) (Sanya, 1-2 m depth), and (0.672 ± 0.004) (Sanya, 4-6 m depth), indicating Φ PSII of corals in Sanya area were higher as compared to corals in Wenchang. Cumulation over the month before sampling showed high correlations with the Symbiodinium density and Φ PSII of P. lutea suggesting that there was a time-lag effect of environmental factors on coral symbiont. Further analysis suggested that SST and nutrients in the reefs were responsible for the observed seasonal variations in symbiont density and Φ PSII of P. lutea, while the spatial difference of Φ PSII probably reflected the coral’s photo acclimation; besides, the cold-water upwelling (Qiongdong upwelling, QDU) had to be taken into account for the variations as well. As the reefs have been experiencing coastal constructing, significant marine culturing and tourist diving activities, the reef waters are at the risk of anthropogenic nutrification, thus, the viability of P. lutea is facing severe threat by the effects of nutrient enrichment and temperature increase. Since local management of nutrient enrichment could reduce the effects of global warming on coral reefs, efficient nutrient management strategies are urgently required to be developed and the action should be taken immediately.

Key words: Hainan Island, Porites lutea, effective photochemical efficiency, Symbiodinium density, seasonal variation