Asynchronous vertical migration and bimodal distribution of motile phytoplankton
Asynchronous vertical migration and bimodal distribution of motile phytoplankton
复制标题
运动浮游植物的异步垂直迁移和双峰分布
DOI：
10.1093/plankt/fbm061
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发表时间：
2007
影响因子：
2.1
通讯作者：
D. Townsend
中科院分区：
文献类型：
--
作者：
D. Ralston;D. McGillicuddy;D. Townsend
一些能动的浮游植物能够在垂直迁移循环中利用深层养分来源：近地表层的光合作用、迁移到深处、吸收限制性养分并运回表层。如果所有四个步骤都可以在 24 小时内完成，那么迁徙就可以与昼夜周期同步，以最大限度地提高光合作用效率。或者，如果生理、行为或环境因素使得循环不可能在 24 小时内完成，则迁移可能是异步的。对浮游植物的许多观察揭示了生物体的双峰垂直分布，最大值靠近表面和营养线。我们使用拉格朗日系综数值模型证明了浮游植物的双峰垂直分布如何可能是异步垂直迁移的症状。我们在类似于缅因湾的条件下模拟了甲藻亚历山大藻的垂直迁移，在缅因湾观察到了甲藻的双峰分布。迁移受到内部营养状态的调节——当氮耗尽时，生物体向下游向硝酸盐，并在吸收营养后返回表面。我们测试了结果对生长速率、氮吸收速率和游泳速度的敏感性，发现生物体分布可以是双峰的或单峰的，具体取决于条件。最后，我们根据生物体特征和营养线深度对种群分布进行分析估计。
Some motile phytoplankton have the capability to exploit deep sources of nutrients in a vertical migration cycle: photosynthesis in the near-surface layer, transit to depth, uptake of the limiting nutrient and transit back to the surface layer. If all four steps can be completed within 24 h, then migrations can be synchronized to the day/night cycle to maximize photosynthetic efficiency. Alternatively, if physiological, behavioral or environmental factors make it impossible for the cycle to be completed in 24 h, then migration may be asynchronous. Many observations of phytoplankton reveal bimodal vertical distributions of organisms, with maxima near the surface and the nutricline. We demonstrate how bimodal vertical distributions of phytoplankton may be symptomatic of asynchronous vertical migration using a Lagrangian Ensemble numerical model. We simulate vertical migration of the dinoflagellate Alexandrium fundyense in conditions similar to those in the Gulf of Maine, where bimodal distributions of A. fundyense have been observed. Migration is regulated by internal nutritional state—organisms swim down toward the nitracline when depleted of nitrogen, and return to the surface after nutrient uptake. We test the sensitivity of the results to growth rate, nitrogen uptake rate and swimming speed, and find that organism distributions can be bimodal or unimodal depending on conditions. Finally, we develop an analytical estimate for population distribution based on organism characteristics and nutricline depth.