Journal of Tropical Oceanography >
Difference of coral skeletal structure revealed by compressive strength measurements
Received date: 2016-07-27
Request revised date: 2016-09-26
Online published: 2017-04-06
Supported by
National Basic Research Program of China (2013CB956104)
National Natural Science Foundation of China (41476038, 41330642, 41372316 and 41676049)
CAS Youth Innovation Promotion Association (2015284)
Copyright
In this study, we measured compressive strength in coral samples from Weizhou Island, northern South China Sea, and the Meiji Reef, the Nansha Islands, southern South China Sea, using uniaxial compressive strength experiments. Differences in coral skeletal structure were revealed using these data, coral reef geological and ecological methods, and the engineering mechanics. The results showed that the uniaxial compressive strength of Meiji corals is approximately three times higher than that of Weizhou corals, indicating that Weizhou corals’ carrying capacity is relatively low. The mechanical properties of Nansha corals showed a character of elastic curve, with a short stage of yield and good ductility. On the contrary, the compressive strength of Weizhou corals has an irregular changing elastic curve character, with multiple compression processes. Based on the observations on the broken samples after compressive experiments, Weizhou samples were not broken on the growth direction of the axis, but in the area of small holes and low density. Increased bioerosion caused changes in the structure of Weizhou coral skeletons, and subsequently poor compressive strength, low bearing capacity, and chaotic mechanical properties. This work demonstrates the effect of water pollution on coral skeletal structure. We suggest that priority should be given to seawater quality protection and control before reef project and coral ecological restoration.
Key words: compressive strength; coral; skeletal structure; bioerosion; South China Sea
JIN Yuxin , CHEN Tianran , MENG Qingshan , HU Minhang . Difference of coral skeletal structure revealed by compressive strength measurements[J]. Journal of Tropical Oceanography, 2017 , 36(2) : 33 -39 . DOI: 10.11978/2016071
Fig. 1 Map of study sites (a) and coral sampling locations. Sites 1, 2, 3, and 4 are located around Weizhou Island, northern South China Sea (b); Site 5 is located on the Meiji Reef of the Nansha Islands (c)图1 研究区域的地理位置(a)以及南海北部涠洲岛(b) 和南沙群岛美济礁(c)上的珊瑚样品的采样点(▲) |
Fig. 2 Cylindrical coral samples used in the experiment. a: W1, b: W2, c: W3, d: W4, e: NS 1, f: NS2-1, g: NS2-2, h: NS3-1, and i: NS3-2. Labels use “Location abbreviations (W: Weizhou Island; NS: Nansha) + sampling sites - sampling number (no for without duplicates).” Coin is used as the scale for 25-mm-diameter图2 实验所用的珊瑚柱状样品 |
Tab. 1 Uniaxial compressive experiment data表1 单轴抗压实验数据 |
编号 | 珊瑚种属 | 采样地点 | 抗压强度/MPa | 平均值/MPa | 弹性模量/GPa | 泊松比 |
---|---|---|---|---|---|---|
W1 | 蜂巢珊瑚 | 1 | 4.91 | 3.76 | 2.259 | 0.191 |
W2 | 滨珊瑚 | 2 | 4.83 | 1.368 | 0.100 | |
W3 | 滨珊瑚 | 3 | 3.74 | 3.218 | 0.415 | |
W4 | 滨珊瑚 | 4 | 1.58 | 2.070 | 0.064 | |
NS1 | 滨珊瑚 | 5 | 8.37 | 10.11 | 6.591 | 0.330 |
NS2-1 | 滨珊瑚 | 5 | 11.65 | 4.883 | 0.101 | |
NS2-2 | 滨珊瑚 | 5 | 7.43 | 2.973 | 0.023 | |
NS3-1 | 滨珊瑚 | 5 | 10.74 | 7.490 | 0.048 | |
NS3-2 | 滨珊瑚 | 5 | 12.34 | 6.909 | 0.063 |
Fig. 3 Histogram of the compressive strength图3 抗压强度柱状图 |
Fig. 4 Profiles of compressive strength time series in Nansha (a) and Weizhou (b) coral samples. Photos on the right are broken corals after compressive experiments. The red dotted lines indicate stages of compression in the process. The time series curves of all Nansha corals are consistent, so we use a solid line to indicate the average value and use shading to show their variation range. In contrast, the curves for the Weizhou coral samples are inconsistent, so we display all of them in the figure.图4 南沙(a)和涠洲岛(b)珊瑚样品的抗压强度时间曲线图 |
The authors have declared that no competing interests exist.
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