南麂海域浮游植物的分布特征

通过对南麂海域2003～2005年4个季节8个航次浮游植物样品的观察,对不同季节浮游植物的种类组成和数量分布进行了分析。研究结果表明,从调查样品中鉴定出浮游植物为3门34属128种。南麂海域的浮游植物密度从4月下旬到12月中、上旬(除赤潮消亡期外),基本保持在107个/m3以上。春季浮游植物以甲藻为主,夏季和冬季以硅藻为主;秋季大部分时间浮游植物以硅藻为主,有时以甲藻为主。能形成该区域赤潮的生物有14种,其中已引发赤潮的生物占6种(甲藻3种,硅藻3种)。春季赤潮为有色赤潮,有较大的危害性;其它季节的赤潮为无色赤潮,未出现危害现象。

Distribution of phytoplankton in the waters of Nanji Archipelago

Species composition and concentration distribution of phytoplankton in different seasons were analyzed through the observation of phytoplanktonic specimens collected in eight cruises in four seasons from 2003 to 2005 in the sea of Nanji Archipelago.128 species of phytoplankton of 3 classes and 34 genera were identified.The concentration of phytoplankton was generally higher than 107 cells/m3 from late April to early December except for the dissipation period of HAB.In spring,dinoflagellate was dominant,while diatom did in summer and winter.In autumn,diatom was dominant in most of the time and sometimes dinoflagellate did.There are 14 species that can cause HAB,in which 6 species(3 species of dinoflagellate and 3 species of diatom) have induced HAB.The spring HAB caused discoloration of the sea water and was harmful while HAB in other seasons caused no discoloration of the sea water and was harmless.Nanji Archipelago is an important marine nature reserve for shellfish and algae in our country,where phytoplankton is not only rich in species but also high in concentration.The area is a good pasture of sea as well as the site where HABs occur frequently.In the past,more studies were done on spring HABs but little was known for other seasons.As indicated by the study,HAB is likely to occur all the year round except for winter,and the HAB mail causative species are Prorocentrum donghaiense and Noctiluca scientillans in spring,Skeletonema costatum,Pseudo-nitzschia pungens,Chaetoceros curvisetus,Thalassionema nitzschioides,Stephanopyxis turris and Rhizosolenia spp.in summer,Alexandrium sp.,Chaetoceros curvisetus,Schroederella delicatula,Ditylum brightwelli and Skeletonema costatum in autumn.Nanji Archipelago lies in the East China Sea and is about 30 nautical miles away from the mainland.To its west is the vast shallow waters of the continental shelf and the northern end of the Taiwan Strait is to its east.This area is directly influenced by the branch of the Taiwan Warm Current and strongly affected by the longshore current,which results in an ecological zone of complicated waters,abundant nutrients,high transparency and little artificial pollution.The special geographical location and excellent environment for water exchange here not only make the phytoplankton rich in species and great in density,but also reduce the harm likely caused by HABs.The active waters and biodiversity in Nanji Archipelago could quickly dilute toxins produced by toxic algae,and mitigate biological suffocation due to too high algal concentration.Except for HABs in spring no harms have been reported for other seasons.HABs in spring mainly harm the cage culture and kelp culture and cause death of small fish less than 10 cm in length.