Ingestion of selected HAB-forming dinoflagellates
几株赤潮甲藻的摄食能力

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 Em-2s-1 light 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 m), 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 Em-2s-1 light intensity (15%) than under 8 Em-2s-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 ingested FLB, FM0.5, and FLA (12.5, 15.5, and 4.5% of individuals, respectively) under both light intensities. A low percentage (9%) of P. minimum individuals 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 (8 Em-2s-1) than the high light intensity (45 Em-2s-1). 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 a proxy for live cells (e.g., bacteria and micro-flagellates) when studying phagotrophy among dinoflagellates. Given the variability in rat