Chemical and biological study of coral reef around the Mauritius : investigation on the bleaching

留尼汪岛是马斯卡林群岛的一部分，位于21°07‘S和55°32’E之间，是一个有210万年历史的火山岛，最早的珊瑚礁殖民可以追溯到公元前8500年，当时海平面比现在低20m。最高点是海拔3069米的内格斯皮顿火山，而活火山皮顿德拉富尔奈斯火山高2631米。岛的面积约为2512平方公里，直径约70公里。常见的礁体地貌包括外坡、内外礁平面和背礁。边缘礁不连续，宽度小于550米，仅占7.3平方公里。在低水位下，礁石露出水面。营养盐浓度很低，硝酸盐浓度在0.2~0.7μμ摩尔之间，磷酸盐浓度在0.0 1~0.0 4μ摩尔之间。浮游动物的丰度出现了波动。海水丰度很低，不超过10斤/L。浮游植物丰度在3000~5000个/L之间，超微蓝藻和微蓝藻类的丰度格局与浮游植物相似。微蓝藻丰度在5500~950个/ml之间波动，ANF在200~600个/ml之间波动，中午细菌丰度较低，晚上(18：00)较高。丰度在100000个细胞/毫升到170000个细胞/毫升之间波动，比其他珊瑚礁的数值低一个数量级。以微微浮游生物(微囊藻和细菌)为食的HNF在晚上18：00表现出与猎物最大丰度一致的最大丰度。珊瑚礁是以高度固氮为基础的健康珊瑚礁。

Reunion Island which is part of the Mascarene archipelago, is located between 21°07'S and 55°32'E. It is a volcanic island 2.1 million years old, with the first reef colonization as a reef bank, dating back to 8500 BC, when the sea level was 20 m lower than it is today. The highest point is the Piton des Neiges 3069 m above sea level while the active volcano, the Piton de la Fournaise, is 2631 m high. The surface area of the island is about 2512 km^2 and the diameter 70 km. The common reef geomorphology includes an outer slope, outer and inner reef flats and a back reef. The fringing reefs are discontinuous and narrow (less than 550 m wide) and they only cover 7.3 km2. The reef flats are exposed at low water. Nutrients concentration was very low with Nitrate ranging from 0.2 to 0.7 μmol, phosphate between 0.01 to 0.04 μmol. Zooplankton abundance fluctuated. Abundance was very low with no more than 10 inds/L of seawater. Phytoplankton abundance varied between 3000 to 5000 cells/l. Pico-phytoplakton as pico-cyanobacteria and ANF followed a similar pattern of abundance with that of phytoplankton. Abundance of pico-cyanobacteria fluctuated between 5500 cell/ml and 950 cells/ml. ANF were scarce fluctuating between 200 to 600 cells/ml. Bacteria were less abundance during at noon but and showed higher abundance at evening (18:00). Abundances fluctuated between 100000 cell/ml to 170000 cells/ml which is one order of magnitude lower that values found in other reefs. HNF which feed onto pico-plankton (picocyano and bacteria) showed their maximum abundance in coincidence with max abundance of their prey at 18:00 in the evening. Coral reef is characterized as healthy coral reef based on the high nitrogen fixation.