Virginia Institute of Marine Science, William & Mary, P.O. Box 1346, Gloucester Point, VA 23062, USA.
Harmful Algae. 2021 Jan;101:101965. doi: 10.1016/j.hal.2020.101965. Epub 2020 Dec 26.
Harmful algal bloom (HAB) dinoflagellate species Karlodinium veneficum and Prorocentrum cordatum (prev. P. minimum) are commonly found in Chesapeake Bay during the late spring and early summer months, coinciding with the spawning season of the eastern oyster (Crassostrea virginica). Unexplained larval oyster mortalities at regional commercial hatcheries prompted screening of oyster hatchery water samples for these HAB species. Both HAB species were found in treated hatchery water during the oyster spawning season, sometimes exceeding bloom cell concentrations (≥ 1,000 cells/mL). To investigate the potential for these HAB species, independently or in co-exposure, to affect larval oyster mortality and activity, 96-h laboratory single and dual HAB bioassays with seven-day-old oyster larvae were performed. Treatments for the single HAB bioassay included fed and unfed controls, K. veneficum at 1,000; 5,000; 10,000; and 50,000 cells/mL, P. cordatum at 100; 5,000; 10,000; and 50,000 cells/mL. Subsequently, the 1,000 cells/mL K. veneficum and 50,000 cells/mL P. cordatum treatments were combined in a co-exposure treatment for the dual HAB bioassay. At all cell concentrations tested, K. veneficum swarmed oyster larvae and caused significant larval oyster mortality by 96 h (Karlo: 21 ± 5%; Karlo: 93 ± 2%; Karlo: 85 ± 3%; Karlo: 83 ± 5%, SE). In contrast, there was no significant difference in larval oyster mortality between the control treatments and any of the P. cordatum treatments by 96 h. By 24 h, larval oysters were significantly less active (immotile) in the presence of either HAB species as compared to control treatments (e.g., Karlo: 37.8 ± 4.1%; Proro: 47.3 ± 7.4%; Fed: 10.8 ± 3.2%; Unfed: 10.1 ± 4.9%, SE). In the dual HAB bioassay, larval oyster mortality associated with 1,000 cells/mL K. veneficum (44 ± 9%, SE) was not changed by the addition of 50,000 cells/mL P. cordatum (55 ± 7%, SE), demonstrating that K. veneficum was primarily responsible for the observed mortality. This study demonstrated that even low cell concentrations of K. veneficum and P. cordatum are harmful to larval oysters, and could contribute to reductions in oyster hatchery production through impacts on this critical life stage.
有害藻类水华（HAB）的旋沟藻属物种卡尔多丁（K. veneficum）和原甲藻（Prorocentrum cordatum）（以前称为 P. minimum）通常在切萨皮克湾春末和初夏出现，正值东方牡蛎（Crassostrea virginica）的繁殖季节。地区商业孵化场出现不明原因的幼虫牡蛎死亡，促使对牡蛎孵化场用水进行这些 HAB 物种的筛查。在牡蛎繁殖季节，在处理过的孵化场水中发现了这两种 HAB 物种，有时超过了水华细胞浓度（≥ 1,000 个细胞/mL）。为了研究这些 HAB 物种，无论是单独还是共同暴露，是否会影响幼虫牡蛎的死亡率和活动，进行了为期 96 小时的实验室单 HAB 和双 HAB 生物测定，使用了 7 天大的牡蛎幼虫。单 HAB 生物测定的处理包括投喂和未投喂对照、1,000 个细胞/mL 的 K. veneficum；5,000 个细胞/mL 的 K. veneficum；10,000 个细胞/mL 的 K. veneficum；和 50,000 个细胞/mL 的 K. veneficum，以及 100 个细胞/mL 的 P. cordatum；5,000 个细胞/mL 的 P. cordatum；10,000 个细胞/mL 的 P. cordatum；和 50,000 个细胞/mL 的 P. cordatum。随后，将 1,000 个细胞/mL 的 K. veneficum 和 50,000 个细胞/mL 的 P. cordatum 处理物在双 HAB 生物测定的共同暴露处理中进行了组合。在所有测试的细胞浓度下，K. veneficum 使牡蛎幼虫群集，并在 96 小时内导致显著的幼虫牡蛎死亡率（Karlo：21±5%；Karlo：93±2%；Karlo：85±3%；Karlo：83±5%，SE）。相比之下，在 96 小时内，控制处理与任何 P. cordatum 处理之间的幼虫牡蛎死亡率没有显著差异。在 24 小时时，与对照处理相比，幼虫牡蛎在存在任何一种 HAB 物种时明显不活跃（不动）（例如，Karlo：37.8±4.1%；Proro：47.3±7.4%；Fed：10.8±3.2%；Unfed：10.1±4.9%，SE）。在双 HAB 生物测定中，与 1,000 个细胞/mL 的 K. veneficum（44±9%，SE）相关的幼虫牡蛎死亡率不受添加 50,000 个细胞/mL 的 P. cordatum（55±7%，SE）的影响，表明 K. veneficum 是导致观察到的死亡率的主要原因。这项研究表明，即使是低浓度的 K. veneficum 和 P. cordatum 对幼虫牡蛎也是有害的，并可能通过对这个关键生命阶段的影响，导致牡蛎孵化场产量的减少。
