Abstract：
Previous research on phytoplankton blooms has often focused on the initiation of blooms, while studies on the mechanisms underlying bloom decline and termination have been more limited. This study aimed to explore the extent of which Acartia tonsa (copepod) grazing does or does not contribute to Margalefidinium polykrikoides (dinoflagellate) bloom decline. M. polykrikoides is a prominent harmful algal bloom (HAB) species that forms dense blooms in coastal and estuarine systems around the world with known ichthyotoxic effects. Sampling occurred in the lower York River Estuary, Virginia, USA in 2021 and 2022 during two M. polykrikoides blooms. Prey removal experiments were conducted using organisms collected from the field to estimate A. tonsa ingestion rates on M. polykrikoides. While A. tonsa was capable of ingesting M. polykrikoides at low abundance, when M. polykrikoides abundance exceeded 2000 cells mL-1, A. tonsa experienced nearly 100% mortality in the 24-hour prey removal experiments. This suggests that A. tonsa likely cannot exert any top-down control on M. polykrikoides blooms, rather, at high concentrations, M. polykrikoides may act as its own grazing deterrent. Extensive M. polykrikoides blooms could therefore continue to persist due to a reduction in grazing pressure, rather than an increase. This would suggest that the decline of M. polykrikoides blooms is likely caused by another factor. As the frequency, duration, and magnitude of HABs are expected to increase in the future, these findings provide key insights to the trophic interactions that may be influencing the duration of M. polykrikoides blooms.
摘要：
以前对浮游植物水华的研究通常集中在水华的开始，而对水华衰退和终止机制的研究则较为有限。这项研究旨在探索放牧Acartiatonsa（co足类）放牧对Margalefidiniumpolykrikoides（鞭毛藻）开花减少的程度。M.polykrikikoides是一种突出的有害藻类水华（HAB）物种，在世界各地的沿海和河口系统中形成密集的水华，具有已知的鱼类毒性作用。采样发生在约克河下游河口，弗吉尼亚,美国将于2021年和2022年两度M.polykrikoides开花。使用从田间收集的生物进行了猎物去除实验，以估计A.tonsa对M.polykrikoides的摄取率。虽然A.tonsa能够以较低的丰度摄入M.polykrikoides，当M.polykrikoides的丰度超过2000个细胞mL-1时，在24小时的猎物去除实验中，A.tonsa的死亡率接近100％。这表明A.tonsa可能无法对M.polykrikikoides开花施加任何自上而下的控制，更确切地说,在高浓度下，波利科德M.可以充当自己的放牧威慑力量。因此，由于放牧压力的降低，大量的M.polykrikoides开花可能会继续存在，而不是增加。这表明M.polykrikoides开花的减少可能是由另一个因素引起的。作为频率，持续时间,预计未来HAB的数量会增加，这些发现为营养相互作用提供了关键的见解，这些相互作用可能会影响多分支杆菌开花的持续时间。
