1998年春季珠江口海域大规模赤潮原因生物的形态分类和生物学特征I

TAXONOMIC AND BIOLOGICAL STUDIES ON CAUSATIVE ORGANISMS FROM A LARGE SCALE RED TIDE OCCURRENCE IN ZHUJIANG RIVER ESTUARY IN THE SPRING, 1998 I

对１９９８年４月１５日采集于广东珠江口万山群岛桂山岛网箱养殖区的赤潮活体水样 和福尔马林固定样品进行优势种的形态分类和生物学特征的研究。结果发现，三宅裸甲藻 （Ｇｙｍｎｏｄｉｎｉｕｍ ｍｉｋｉｍｏｔｏｉ）是此次赤潮的最优势种，最高密度达到 ７．６ × １０６ｃｅｌｌｓ／Ｌ。另两种优 势种为斯氏多沟藻（Ｐｏｌｙｋｒｉｋｏｓ ｓｃｈｗａｒｔｚｉｉ）和螺旋螺沟藻（Ｇｙｒｏｄｉｎｉｕｍ ｓｐｉｒａｌｅ），其最高密度分 别达到 １．１× １０５ｃｅｌｌｓ／Ｌ和 １０４－１０５ｃｅｌｌｓ／Ｌ。此次赤潮的原因生物都属于裸甲藻类，死后或用 福尔马林固定后细胞要么立即裂解，要么变形缩小。有些种类如螺旋螺沟藻在固定样品中找 不到其踪迹，因而无法精确计数。本文描述的３种赤潮藻在细胞、色素体、核、上锥沟和链状群 体等形态构造及外观上与国外学者所描述的几乎完全一致，只是细胞比日本海域产的稍小。 这可能与珠江口海域纬度较日本低有关。电镜照片显示三宅裸甲藻有一明显的上锥沟，斯氏 多沟藻则营养细胞和孢囊同时存在。

A large scale harmful algal bloom occurred in the Zhujiang River estuary on the South China Sea Coast from March to April in 1998, and caused a great economic loss on the local fish farming. Optical microscope and scanning electron microscope, we studied morphological features of the causative organisms sampled from the most hit area-a tanked fish farm near Guishan Island located on the west side of the Zhujiang River estuary, Chick on April 15th 1998 when the bloom was on its peak. At the same time, counting on the populations was made for the species that could be judged in the samples preserved by formalin. The most dominant causative orphism of the bloom (7.6 × 106cells/L) was identified to be Gymnodinium mikimotoi Miyake et Kominami ex Oda. Two other dominant species Polykrikos schwartzii Butschli (1.1 × 105cells/L) and Gyrodinium spirale Bergh (104-105cells/L) are also discussed in the present paper, and another four red tide causative organisms will be discussed in the following paper. Gym. mikimotoi with a cell length 15.6-31.2μm and width 13.2-24μm. The cells slightly were flattened dorso-ventrally. The epicone looks sub-hemispherical to broadly conical with an apical groove extenting from the right of cingulum to the ventral. The nucleus is ellipsoidal to reniform, and there were 10- 16 chloroplates scattered in the cells. P. schwartzii was always coonial, consisting of four to eight gymmodinioid with with one nucleus per two units. The colony was 80- 130μm in length and 40-55μm in width, but each tnt shortly columnar with girdle and sulcus, lacking pigments. Its cysts were also found in the samples, ellipsoidal and dark brown in color and covered with coaserly reticulate, shelf-like and/or spinous ornaments. Gyr. spirale looked spindle in shape, with a 55-80μm in length and a 22-32μm in width. Cirdle was marrow and displaced in more than I / 3 of cell length. There were clear straps extending from epicone to hypocone. No photosynthetic pigments were found. When the cell movement stopped, the organism died and collapsed almost at once. All these red tide organisms belong to unarmored dinoflagellate, and after they died or were preserved by formalin, they would collapse or transform rapidly. So, some species such as Gyr. spirale could not be counted precisely in the preserved samples. The morphological structures like appearance, chloroplast nucleus, apical groove, cyst colony and so on for these three species discussed in the present paper were much similar to those found in other countries. However, the size of organisms was slightly smaller than that distributed in the Japanese waters, probably because the latitude of the Zhujiang River estuary is lower than that in Japan. Although the density of organisms was not so high and the duration was just two days, the bloom made a severe loss on the local fish farming. This indicated that the unarmored dinoflagellate bloom was very harmful to marine ecological system and fish farming.