东海原甲藻(Prorocentrum donghaiensis)对原生动物群落结构影响的现场船基实验

2005年在长江口赤潮频发海域调查期间，分别于4月27日、5月4日和5月8日，在zzf1、zc18a和ra5站位利用现场船基培养的方法，研究了添加到赤潮密度10^6cells L^-1的东海原甲藻（Prorocentrum donghaiense）对原生动物群落结构的影响。结果发现，赤潮密度的东海原甲藻抑制了小型无壳纤毛虫的种群数量，而没有抑制中大型砂壳纤毛虫和夜光虫（Noctiluca scintillans）的种群数量，从而使得原生动物群落向中大型种类演替，这种影响的程度与原生动物本身的群落组成和浮游植物的组成密切相关。添加东海原甲藻72h后，在以小型无壳纤毛虫管游虫（Cyrtostrombidium sp．）为优势种的zzf1站位，演替为以大型原生动物夜光虫为优势种的群落；在以中大型原生动物百乐拟铃虫（Tintinnospsis beroidea）和夜光虫为优势种的zc18a站位，仍然是以此为优势种，且大型原生动物夜光虫在群落中的比例上升；在以小型无壳纤毛虫急游虫2（Strombidium sp．2）为优势种的ra5站位，演替为以中大型原生动物百乐拟铃虫和亚速岛网纹虫（Favella azorica）为优势种的群落。zzf1和ra5站位实验组中原生动物的总丰度都呈下降趋势，而zc18a站位变化不明显，这是由于前两个站位的最优势种管游虫（zzf1站位）和急游虫2（ra5站位）的丰度迅速下降，而zc18a站位的优势种百乐拟铃虫和夜光虫的丰度比较稳定造成的。在zzf1和zc18a站位，对照组和实验组中原生动物的总生物量在实验前后都没有大的变化，而在ra5站位却均呈下降的趋势。这可能与浮游植物的组成有关，zzf1和zc18a站位是以无毒的锥状斯氏藻（Scrippsiella trochoidea）和螺旋环沟藻（Gyrodinium spirale）为主，而ra5站位是以有毒的亚历山大藻（Alexandriumsp．）为主。综上可见，可预测当东海大规模赤潮爆发时，会使原生动物群落向中大型种类演替，进而可能影响海洋生态系统的结构和功能。

A shipboard study of the effects of HAB species Prorocentrum donghaiense on protozoan communities at three sites in the East China Sea, involving 72h inoculation experiments to simulate HAB bloom events

To study the effects of simulated HAB (Harmful algal blooms) on protozoan community structure, shipboard Prorocentrum donghaiense inoculation experiments (at about 106 cells L-1, equivalent to bloom density) were carried out at stations zzf1, zc18a and ra5 in the East China Sea, a frequent HAB occurrence area, on 27th April, 4th May and 8th May 2005, respectively. The results showed that P. donghaiense at a density of 106 cells L-1 could inhibit the abundance of small-sized aloricate ciliates, but had no significant effect on medium- and large-sized protozoa, which thereby led to a community succession toward medium- or large-sized individuals. Such effects and the degree of impact were closely related to both protozoan and phytoplankton community compositions. At station zzf1, the protozoan community initially dominated by the small-sized aloricate ciliate Cyrtostrombidium sp. changed remarkably and was dominated by the large-sized protozoan Noctiluca scintillans after adding P. donghaiense for 72 h. At station zc18a, the protozoan community initially dominated by medium-sized tintinnid Tintinnopsis beroidea and N. scintillans was still dominated by the two protozoa, and the dominant degree of N. scintillans increased noticeably after adding P. donghaiense for 72 h. At station ra5, the protozoan community initially dominated by the small-sized aloricate ciliate Strombidium sp.2 changed dramatically and was dominated by T. beroidea and the large-sized tintinnid Favella azorica at the end of the experiment. The total abundance of protozoa decreased dramatically at stations zzf1 and ra5 due to the reduction of their dominant species Cyrtostrombidium sp. and Strombidium sp.2, whereas no significant variation was found at station zc18a due to the steady abundance of its dominant species T. beroidea and N. scintillans after adding P. donghaiense for 72 h. The total biomass of protozoa at stations zzf1 and zc18a changed slightly in both control groups and the experimental ones. In contrast, total biomass decreased drastically at station ra5 at the end of the experiments, which might be due to the different phytoplankton composition at the three stations: station zzf1 and zc18a were dominated by non-toxic Scrippsiella trochoidea and Gyrodinium spirale, however station ra5 was dominated by toxic Alexandrium sp.. These results indicate that large scale P. donghaiense HAB could affect protozoan communities and might further exert a profound influence on the structure and function of marine ecosystems.