Ecology of oceanic coccolithophores.: I.: Nutritional preferences of the two stages in the life cycle of Coccolithus braarudii and Calcidiscus leptoporus
Ecology of oceanic coccolithophores.: I.: Nutritional preferences of the two stages in the life cycle of Coccolithus braarudii and Calcidiscus leptoporus
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DOI：
10.3354/ame044291
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发表时间：
2006-10-10
影响因子：
1.4
通讯作者：
Billard, Chantal
中科院分区：
文献类型：
--
作者：
Houdan, Aude;Probert, Ian;Billard, Chantal
布氏球藻(Coccolius Braarudii)和瘦柄球藻(CalciDisus Leptoporus)是2个球藻纲(Prymnesio-Phyceae：Haptophyta)球藻，具有复杂的异形生活史，在运动的含全球藻的单倍体阶段和非运动的含异球藻的二倍体阶段之间交替。球藻生物这种类型的生命周期对生态的影响目前知之甚少。通过改变它们的生长条件，研究了两个物种每个阶段的营养偏好，以及它们对湍流条件的生长反应。在所测试的不同培养基中，只有合成海水培养基不支持布拉鲁迪氏梭菌和纤毛虫的生长。在天然海水培养条件下，土壤浸出物(K/2：0.23+/-0.02d(-1))和K/2+土壤浸出物(0.35+/-0.01d-1)能促进两种球藻单倍体阶段的生长，而二倍体阶段则没有，这表明游动阶段能够利用土壤浸出物中存在的化合物或摄取在浓缩培养基中激活的细菌。在培养液中加入醋酸钠也刺激了布拉鲁迪氏隐孢子虫的单倍体阶段，使用标记细菌的进一步实验证明了这一运动阶段的吞噬能力。不同营养浓度对两种鱼生长速率的影响表现出明显的差异，在营养丰富的培养基中，二倍体阶段的生长速率较高(K/2：0.34+/-0.04d-1，K/25：0.29+/-0.01d(-1)，K/100：0.16+/-0.01d(-1))。两种球藻对物理湍流的响应也不同，单倍体鞭毛阶段对混合反应敏感，而非运动二倍体阶段更具抗性。这些实验结果有力地表明，Braarudii和Cletoporus的每个形态阶段对应着不同的生态位，根据野外观察，活动单倍体阶段比二倍体非活动阶段更稳定的寡营养生态位。Margalef的二维浮游植物生态位空间模型(1978年；海洋学报1：493-509)根据营养物质和湍流的定义对其进行了修正，以纳入这一假设。
Coccolithus braarudii and Calcidiscus leptoporus are 2 coccolithophores (Prymnesio-phyceae: Haptophyta) known to possess a complex heteromorphic life cycle, with alternation between a motile holococcolith-bearing haploid stage and a non-motile heterococcolith-bearing diploid stage. The ecological implications of this type of life cycle in coccolithophores are currently poorly known. The nutritional preferences of each stage of both species, and their growth response to conditions of turbulence were investigated by varying their growth conditions. Of the different culture media tested, only the synthetic seawater medium did not support the growth of both stages of C. braarudii and C. leptoporus. With natural seawater-based media, the growth rate of the haploid phase of both coccolithophores was stimulated by the addition of soil extract (K/2: 0.23 +/- 0.02 d(-1) and K/2 with soil extract 0.35 +/- 0.01 d-1 for the C. braarudii haploid stage), while the diploid phase was not, indicating that the motile stage is capable of utilizing compounds present in soil extract or ingesting bacteria that are activated in enriched media. The addition of sodium acetate to the medium also stimulated the haploid phase of C. braarudii, and further experiments using labeled bacteria demonstrated the capacity for phagotrophy of this motile stage. The effect of nutrient concentrations on the growth rates of both species was evaluated, showing clear differences between the 2 phases of the life cycle, with higher growth rates for the diploid stage in nutrient-rich media (K/2: 0.34 +/- 0.04 d-1, K/25: 0.29 +/- 0.01 d(-1), K/100: 0.16 +/- 0.01 d(-1) for the haploid stage of C. leptoporus). Responses of the 2 phases of both coccolithophores to physical turbulence were also different, with a haploid flagellate stage sensitive to mixing and a more resistant non-motile diploid stage. The results of these experiments strongly indicate that each morphological stage of C. braarudii and C. leptoporus corresponds to a different ecological niche, the motile haploid stage exploiting a more stable oligotrophic niche than the diploid non-motile stage, in accordance with field observations. The 2-dimensional phytoplankton niche space model of Margalef (1978; Oceanol Acta 1:493-509), defined by nutrients and turbulence, was amended to integrate this hypothesis.