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

留尼汪岛是马斯克林群岛的一部分，位于南纬21°07 '和东经55° 32'之间。它是一个火山岛，有210万年的历史，第一个珊瑚礁殖民地作为珊瑚礁银行，可以追溯到公元前8500年，当时海平面比今天低20米。最高点是海拔3069米的Piton des Neiges，而活火山Piton de la Fournaise高2631米。该岛的表面积约为2512平方公里，直径为70公里。常见的礁地貌包括外斜坡、外礁坪、内礁坪和后礁。边缘礁不连续且狭窄（宽度小于550米），仅覆盖7.3平方公里。礁滩在低潮时露出水面。营养盐浓度很低，硝酸盐在0.2 ~ 0.7 μmol之间，磷酸盐在0.01 ~ 0.04 μmol之间。浮游动物丰度波动。海水盐度很低，不超过10 inds/L。浮游植物丰度在3000至5000细胞/升之间变化。微植藻作为微蓝藻和ANF遵循与浮游植物相似的丰度模式。微蓝细菌的数量在5500 ~ 950 cells/ml之间波动。ANF很少在200 ~ 600个/ml之间波动。细菌在中午的丰度较低，而在晚上（18：00）的丰度较高.丰度波动在100000细胞/毫升至170000细胞/毫升，这是一个数量级低于其他珊瑚礁中发现的值。以微微型浮游生物（picocyano和细菌）为食的HNF在晚上18：00显示出其最大丰度与其猎物的最大丰度一致。珊瑚礁是一种健康的珊瑚礁，其特征在于其具有较高的固氮作用。

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.