Yukun GE，Jun XUZhongguancun High School in Haidian District of Beijing City，Beijing 100086

Correlation Analysis between Bleaching Rate of Brain Coral and Trace Elements Contents in Seawater

Yukun GE，Jun XU*
Zhongguancun High School in Haidian District of Beijing City，Beijing 100086

Brain coral is mainly distributed in the Great Lameshur Bay of the U.S. Virgin Islands in the Caribbean.It has very rare species，but the bleaching phenomenon is severe.In this study，the numbers and bleaching rates of brain corals in the sampling plots were investigated，and the trace elements contents in the seawater were determined with inductively coupled plasma-mass spectrometry（ICPMS）.Then the correlation between the bleaching rate of brain coral and trace elements contents in seawater was analyzed.The results showed that under temperature of 27.83-28.88℃，pH of 8.5-8.7，salinity of 32.74%-34.04%and depth of 0-4 m，there were V，Cr，Rb，Sr，Ag and other trace elements in seawater.When the V content was lower than 99.1 ng/ml，the bleaching rate of brain coral was weakly correlated to V content in seawater；when the Cr content was lower than 23.5 ng/ml，the bleaching rate of brain coral was correlated to Cr content；when the Ag content ranged from 34.1-56.3ng/ml，there was a significant correlation between bleaching rate of brain coral and Ag content in seawater.

Brain coral；Bleaching rate；Trace element；Correlation

C oral reef ecosystems have very important ecological functions.They provide a place for spawning，reproduction，inhabiting and avoiding predators to many marine organisms.However，the coral bleaching has led to severe degradation of coral reefs.The foreign and domestic studies have shown that the coral bleaching is resulted from following factors:increased temperature［1-10］，ultraviolet radiation（solar radiation）［11］，low temperature［12-15］，chemical contaminants［16-17］，bacterial infection［18］，diseases［19］and compound factors［20］.

In this study，the number and bleaching rate of brain coral（Diploria strigosa）in the Great Lamshur Bay of the U.S.Virgin Islands were investigated and analyzed.In addition，the trace elements contents in seawater were determined so as to investigate the correlation between bleaching rate of brain coral and trace elements contents in seawater.Thus the causes of coral bleaching will be found，thereby providing a reference for development of control measures and protecting marine species.

lnvestigation Site

The investigation point was located in the Great Lameshur Bay（64°44′-64°48′E，18°16′-18°18′）（Fig.1）.

lnvestigation Object

Brain coral is rounded，and there are many grooves on its surface.So the appearance of brain coral is similar to that of human brain （Fig.2）.The brain coral in the seawater around the ST John Island is mostly brown or tan. It lives mainly in the warm shallow waters.Brain coral has a long life that can be up to 900 years.Moreover，its body type is larger，and the larger one can be as high as 1.8 m.

Methods

The health status of brain coralwas diagnosed with coral health card. The number of brain coral in the investigation point was investigated with transect sampling method.The all elements contents in the seawater were determined with the ICP-MS （X II，ThermoFisher，US）in the Detection and Analysis Center of the Tsinghua University.The salinity in seawater was determined with the portable salinity meter（Master-A，Japan）.The pH of seawater was detected with the portable pH meter （MT-8061，US）. Considering the collection of seawater samples，in the horizontal direction，four cross-shaped sampling points with brain coral in the center were designed（25 ml/point）；in the vertical direction，the three sampling points in which coral bleaching rate was 0，0＜coral bleaching rate≤10%and coral bleaching rate ＞10% respectively were designed.All the data was processed and analyzed with Excel.

Coral bleaching rate=Coral bleaching area/Transect sampling area× 100% （2）

Results and Analysis

Seawater quality

General parameters The values of general parameters were all obtained at local 02:00 pm in situ.As shown in Table 1，there was little change in seawater temperature.In the 0-4 m of shallow water，the salinity and pH of seawater were also relatively stable under regulation of waves and flow.

Analysis on all elements in seawater As shown in Table 2，the average contents of Ca，K，Mg，Na and S in seawater were 0.446 6， 1.388 2，11.86，0.431 8 and 0.985 3 mg/ml.Among the 5 samples，the variances of the Ca，K，Mg，Na and S contents were 0.000 020，0.000 641，0.022 056，0.000 131 and 0.000 025，respectively.It was indicated the Ca，Mg，K，Na and S contents were relatively stable in different-depth seawaters.

Table 3 showed that among the 5 samples，the variances of the V，Cr，Rb，Sr and Ag contents were 4.777 6，15.594 4，0.237 6，0.003 9 and 279.592 4，respectively.It was suggested that the Ag，Cr and V contents in seawater fluctuated in varying degrees，while the Rb and Sr contents showed relatively small fluctuations.Compared to those of Ag，Cr and V，the contents of Rb and Sr in seawater were relatively stable.

Correlations between coral number and bleaching rate and water depth

The numbers and health statuses of brain corals in different-depth seawaters in the investigation point were shown in Table 4.

As shown in Table 4，the brain coral in the investigation point was mainly brown or tan.The correlation between the number of brain coral and seawater depth was further analyzed（Fig.3）.

As shown in Table 4 and Fig.3，there were only a small number of brain corals in Great Lameshur Bay. There were even no brain coral in the 4 out all the plots.Among the plots，the largest number of brain coral was 6. So the difference between extreme values reached6，indicating an uneven distribution of brain coral. Based on correlation analysis，a regression equation was obtained:y= -0.042x+2.329 8 （R2=0.000 4）.It was suggested the growth of brain coral was not related to seawater depth.

Table 1 General parameters

Table 2 Salinity components contents and S content in different-depth seawaters

Table 3 Trace elements contents in different-depth seawaters

Correlations between coral bleaching rate and trace elements contents in seawater

The temperature，pH and salinity of seawater in the investigation point were relatively stable.The analysis on all elements in seawater also showed that the Ca，K，Mg，Na and S contents were stable，and the Rb and Sr contents were relatively stable. Therefore，it was speculated that the bleaching rate of brain coral was related to V，Cr and Ag contents in seawater.The correlations between the 3 trace elements contents and the bleaching rate were further analyzed.

Correlation between coral bleaching rate and V content in seawater Table 3 and Fig.4 showed that when the V content in seawater was lower than 99.1 ng/ml，the regression equation between bleaching rate of brain coral（y）and V content in seawater （x）was y=1.054 1x-95.435（R2=0.056 6）.It was indicated there was a weak correlation between bleaching rate of brain coral and V content in seawater.

Correlation between coral bleaching rate and Cr content in seawater Table 3 and Fig.5 showed that when the Cr content in seawater was lower than 23.5 ng/ml，the regression equation between bleaching rate of bran coral（y）and Cr content in seawater（x）was y=1.730 9x-26.237（R2=0.498 3），indicating a correlation between bleaching rate of brain coral and Cr content in seawater.

Table 4 Seawater depths，brain coral numbers and bleaching rates

Correlation between coral bleaching rate and Ag content in seawater As shown in Table 3 and Fig.6，when the Ag content inseawater was lower than 56.3 ng/ml，the regression equation between bleaching rate of brain coral（y）and Ag content in seawater（x）was y= 0.552 5x-8.766 2（R2=0.910 4）.The determination coefficient was close to 1，so there was a great correlation between bleaching rate of brain coral and Ag content in seawater.

Conclusions and Prospect

Combining the field investigation and data analysis，it can be concluded that the growth of brain coral is not related to seawater depth；when the V content in seawater is lower than 99.1 ng/ml，the bleaching rate of brain coral is not affected by V content；when the Cr content in seawater is lower than 23.5 ng/ml，Cr content has certain effect on bleaching rate of brain coral，so the Cr content in seawater should be monitored regularly；when the Ag content in seawater ranges from 34.1 to 56.3 ng/ml，Ag content has great effect on bleaching rate of brain coral，so the Ag contamination control should be enhanced，thereby reducing the bleaching rate of brain coral.However，the influence degrees and mechanisms of elements on bleaching rate of brain coral are still needed to be studied further.

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腦珊瑚白化率與海水微量元素的相關(guān)性分析——美屬維爾京群島珊瑚科學(xué)考察

腦珊瑚（Diploria strigosa）主要分布在大西洋的加勒比海地區(qū)的美屬維爾京群島圣約翰島Great Lameshur Bay，種類(lèi)很少，珊瑚白化現(xiàn)象嚴(yán)重。該文采用樣帶場(chǎng)地調(diào)查腦珊瑚數(shù)量和白化率統(tǒng)計(jì)法，結(jié)合電感耦合等離子體質(zhì)譜儀測(cè)試技術(shù)對(duì)海水中微量元素檢測(cè)分析，對(duì)腦珊瑚白化率與微量元素的相關(guān)性進(jìn)行分析，結(jié)果表明：水溫27.83～28.88℃、pH值8.5～8.7、鹽度32.74%～34.04%，海水深度0～4m，微量元素有V、Cr、Rb、Sr、Ag。釩（V）含量低于99.1 ng/ml，腦珊瑚白化率與釩（V）元素含量有弱相關(guān)性；鉻（Cr）含量低于23.5ng/ml，腦珊瑚白化率與鉻（Cr）元素含量有相關(guān)性；銀（Ag）含量在34.1～56.3 ng/ml范圍，腦珊瑚白化率與銀（Ag）元素含量具有很強(qiáng)的相關(guān)性。

腦珊瑚；白化率；微量元素；相關(guān)性

葛宇堃（1998-），男，江西贛州人，高中生，特長(zhǎng)生物，E-mail：gykleo@126.com。*通訊作者，特級(jí)教師，從事生物方面的教學(xué)研究，E-mail：donenxj@163.com。

2014-12-19

2015-02-11

.E-mail:donenxj@163.com

December 19，2014Accepted:February 11，2015