几株赤潮甲藻的摄食能力

Ingestion of selected HAB-forming dinoflagellates

采用荧光标记的方法,在营养盐限制条件下,对6株赤潮甲藻对荧光标记的海洋细菌(FLB)、金藻(FLA)和两种粒径分别为0.5μm和2.0μm的荧光微球(FM0.5和FM2.0)4种摄食对象的摄食进行了比较研究。研究结果表明,除了东海原甲藻对4种摄食对象均没有摄食外,其它5株甲藻,微小亚历山大藻、链状亚历山大藻、塔玛亚历山大藻、海洋原甲藻和微小原甲藻均具有摄食能力,但对摄食对象的选择和摄食率有差异,多数摄食率是在4 h达到最大,白天的摄食能力强于夜间。研究说明了在营养盐限制环境中,有些具有兼性营养能力的甲藻对细菌和/或更小浮游植物的摄食能力可能对维持和促进其生长具有不可忽视的作用。

The ingestion behavior of six dinoflagellate species isolated from the Chinese and Korean coasts was evaluated in this paper. These six species include Prorocentrum donghaiense, P. micans, P. minimum, Alexandrium minutum, A. catenella, and A. tamarense, which often contribute to the formation of harmful algal blooms （HABs）. They were cultured under either 45 or 8 μEm^-2 s^-1light intensities, in nutrient-depleted culture medium containing different particles, such as fluorescently labeled dead marine bacteria （FLB） , the dead marine micro-flagellate Isochrysis galbana （FLA） , and the fluorescent microspheres of two sizes （ FM0. 5 and FM2. 0, sphere diameter 0.5 and 2.0 μm） , respectively. The ingestion activities were quantified by calculating the percentage of dinoflagellates that ingested either FLB, FLA, FM0. 5, or FM2. 0, based on the observation of 100 dinoflagellate cells in each group. In our experiment, the ingestion behaviors were observed in A. minutum, A. catenella, A. tamarense, P. micans, and P. minimum. And they all showed great different efficiency in choosing different particle to ingest. For example, A. minutum could ingest both FM0.5 and FLA, though a higher percentage of individuals exhibited ingestion behavior under 45 μEm^-2 s^-1 light intensity （ 15 % ） than under 8 μEm^-2 S^-1（2% ）. Similarly, A. catenella ingested FLB, FM0.5, and FLA （5.5%, 7.5%, and 6% individuals of the total population to ingest, respectively） under both light intensities. A. tamarense was able to ingest only FLB and FM0.5 under the low light intensity （7% and 9% of individuals, respectively）. P. micans i 15.5% , and 4. 5% of individuals, respectively） under both light intensities. ngested FLB, FM0.5, and FLA （ 12.5%, A low percentage （9%） of P. minimumindividuals ingested FM0.5, and we observed ingestion under both light intensities. At the same time, it is found that the ingestion behavior showed a peak at 4 h after the ingestion objects were introduced to the medium, and it occurred primarily during the daytime. To our knowledge, this is the first report about the ingestion of I. galbana by A. minutum and both I. galbana and marine bacteria by A. catenella. The percentage of individuals exhibiting ingestion behavior was generally lower at the low light intensity （8μEm^-2 s^-1） than the high light intensity （45μEm^-2 s^-l）. Our results showed that ingestion ability was controlled/regulated by inorganic nutrient concentration, not by organic carbon. Given the variability in ingestion behavior, the environmental factors regulating ingestion likely differ among the dinoflagellate species. In this paper, the ingestion ratios on FLA were low. Because the fluorescently labeled I. galbana was motionless （dead）, which may have affected recognition by the dinoflagellates, thus reducing the rate of ingestion. We evaluated the use of fluorescent microspheres as the proxies for live cells （e. g., bacteria and micro-flagellates ） when studying phagotrophy among dinoflagellates. Given the variability in rates of consumption, our results suggest that fluorescent microspheres are not a suitable replacement for live cells. Interestingly, we demonstrated that these dinoflagellates, which have generally been considered to be autotrophic, have the ability to ingest other cells suggesting they should be classified as mixotrophic. Thus, it was hypothesized that these dinoflagellate species have an effect on the abundance of bacteria or/and smaller phytoplankton in natural ecosystems. In conclusion, the ingestion ability of dinoflagellates likely plays an important role in the formation and maintenance of HABs. Through this study, a new scientific perspective is provided for the formation mechanism of HABs