Institute for Marine and Antarctic Studies (IMAS), University of Tasmania, Private Bag 129, Hobart, Tasmania 7001, Australia.
Institute for Marine and Antarctic Studies (IMAS), University of Tasmania, Private Bag 129, Hobart, Tasmania 7001, Australia.
Harmful Algae. 2016 May;55:238-249. doi: 10.1016/j.hal.2016.03.020. Epub 2016 Apr 9.
The detection of sparse Alexandrium catenella-resting cysts in sediments of southern Chilean fjords has cast doubts on their importance in the recurrence of massive toxic dinoflagellate blooms in the region. The role of resting cysts and the existence of different regional Chilean populations was studied by culturing and genetic approaches to define: (1) cyst production; (2) dormancy period; (3) excystment success; (4) offspring viability and (5) strain mating compatibility. This study newly revealed a short cyst dormancy (minimum 69 days), the role of key abiotic factors (in decreasing order salinity, irradiance, temperature and nutrients) controlling cyst germination (max. 60%) and germling growth rates (up to 0.36-0.52div.day). Amplified fragment length polymorphism (AFLP) characterization showed significant differences in genetic distances (GD) among A. catenella populations that were primarily determined by the geographical origin of isolates and most likely driven by oceanographic dispersal barriers. A complex heterothallic mating system pointed to variable reproductive compatibility (RCs) among Chilean strains that was high among northern (Los Lagos/North Aysén) and southern populations (Magallanes), but limited among the genetically differentiated central (South Aysén) populations. Field cyst surveys after a massive 2009 bloom event revealed the existence of exceptional high cyst densities in particular areas of the fjords (max. 14.627cystscm), which contrast with low cyst concentrations (<221.3cystscm) detected by previous oceanographic campaigns. In conclusion, the present study suggests that A. catenella resting cysts play a more important role in the success of this species in Chilean fjords than previously thought. Results from in vitro experiments suggest that pelagic-benthic processes can maintain year-round low vegetative cell concentrations in the water column, but also can explain the detection of high cysts aggregations after the 2009-bloom event. Regional drivers that lead to massive outbreaks, however, are still unknown but potential scenarios are discussed.
智利南部峡湾沉积物中稀疏亚历山大藻休眠孢囊的检测对该地区大规模有毒甲藻水华重现的重要性提出了质疑。通过培养和遗传方法研究休眠孢囊和不同区域智利种群的存在，以确定：（1）孢囊产生；（2）休眠期；（3）出囊成功率；（4）后代活力和（5）菌株交配相容性。本研究首次揭示了较短的休眠孢囊（最短 69 天），关键非生物因素（按降序排列：盐度、光照、温度和营养物质）控制孢囊萌发（最高 60%）和幼体生长率（高达 0.36-0.52 分裂/天）的作用。扩增片段长度多态性（AFLP）特征分析显示，亚历山大藻种群的遗传距离（GD）存在显著差异，这些差异主要由分离株的地理起源决定，最有可能是由海洋扩散障碍驱动的。复杂的异宗交配系统表明，智利菌株之间的生殖相容性（RC）存在差异，北部（洛斯 Lagos/北 Aysén）和南部种群（马格丽特群岛）之间的 RC 较高，但遗传分化的中部（南 Aysén）种群之间的 RC 有限。2009 年大规模水华事件后进行的现场孢囊调查显示，峡湾特定区域存在异常高的孢囊密度（最高 14.627 个孢囊/cm），这与先前海洋学考察中检测到的低孢囊浓度（<221.3 个孢囊/cm）形成对比。总之，本研究表明，与以前的想法相比，亚历山大藻休眠孢囊在智利峡湾中该物种的成功中发挥了更重要的作用。体外实验结果表明，浮游-底栖过程可以维持水柱中全年低营养细胞浓度，但也可以解释 2009 年水华事件后高孢囊聚集的检测。然而，导致大规模爆发的区域驱动因素仍不清楚，但讨论了潜在的情景。
