海南岛澄黄滨珊瑚共生藻对环境变化的适应性

在全球气候变暖和人类活动加剧导致珊瑚礁严重衰退的背景下，以抗逆性强的澄黄滨珊瑚（Porites lutea）为研究对象，于 2013 年 10 月―2014 年 8 月在海南岛文昌和三亚对其共生藻密度及光合效率开展了季节性调查研究。结果显示：1）澄黄滨珊瑚共生藻的密度及光合效率均存在显著的季节变化，共生藻密度在冬季最低、夏季较高，其光合效率在冬季较高，春夏季较低。2）澄黄滨珊瑚共生藻密度的空间差异远小于其季节变化的差异，但水深 1~2 m 澄黄滨珊瑚共生藻的密度普遍高于水深 4~6 m 的澄黄滨珊瑚，三亚澄黄滨珊瑚共生藻的光合效率明显高于文昌。3）进一步分析发现，在诸多环境因子中，海表温度 SST 和水体营养是驱动海南岛澄黄滨珊瑚共生藻密度及光合效率变化的主要环境因素，而光合效率的空间差异则可能是珊瑚对生存环境长期驯化的结果。由于文昌和三亚沿岸海水养殖和潜水旅游等人类活动频繁，礁区海水面临富营养化的风险，推测海南岛澄黄滨珊瑚面临 SST 上升和营养胁迫联合效应的严重威胁。

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

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.