Increasing costs due to ocean acidification drives phytoplankton to be more heavily calcified: optimal growth strategy of coccolithophores.
Increasing costs due to ocean acidification drives phytoplankton to be more heavily calcified: optimal growth strategy of coccolithophores.
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DOI：
10.1371/journal.pone.0013436
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发表时间：
2010-10-15
期刊：
影响因子：
3.7
通讯作者：
Calosi P
中科院分区：
文献类型：
--
作者：
Irie T;Bessho K;Findlay HS;Calosi P
海洋酸化可能是海洋生态系统和全球碳循环的最大威胁之一。在钙化生物中，颗石藻受到了特别的关注，因为它们的方解石沉淀在向深海的碱度通量中起着重要作用（即，无机碳泵）。目前，经验的努力致力于评估塑料对酸化的反应，但这种方法缺少进化的考虑。因此，我们构建了一个优化模型来评估球石动物的生活史的进化反应，假设他们的外骨骼（球石），以减少瞬时死亡率。我们的模型预测，自然选择有利于构建更严重的钙化外骨骼，以应对酸化驱动的成本增加。这种违反直觉的反应之所以发生，是因为在酸性更强的条件下选择更好的防御、更慢的生长策略所带来的健康益处超过了加速细胞周期的益处，因为这是通过产生更少的钙化外骨骼来实现的。与普遍认为的相反，进化优化的种群可以在酸化程度更高的海水中的水华期间沉淀出更大量的CaCO3，这取决于参数值。这些研究结果表明，海洋酸化可能会提高海洋生物的钙化率，作为一种适应性反应，可能伴随着更高的固碳能力。我们的理论也提供了一个令人信服的解释，从2000年前到现在的多物种化石时间序列记录，其中平均颗石的大小增加了沿着大气CO2浓度。
Ocean acidification is potentially one of the greatest threats to marine ecosystems and global carbon cycling. Amongst calcifying organisms, coccolithophores have received special attention because their calcite precipitation plays a significant role in alkalinity flux to the deep ocean (i.e., inorganic carbon pump). Currently, empirical effort is devoted to evaluating the plastic responses to acidification, but evolutionary considerations are missing from this approach. We thus constructed an optimality model to evaluate the evolutionary response of coccolithophorid life history, assuming that their exoskeleton (coccolith) serves to reduce the instantaneous mortality rates. Our model predicted that natural selection favors constructing more heavily calcified exoskeleton in response to increased acidification-driven costs. This counter-intuitive response occurs because the fitness benefit of choosing a better-defended, slower growth strategy in more acidic conditions, outweighs that of accelerating the cell cycle, as this occurs by producing less calcified exoskeleton. Contrary to the widely held belief, the evolutionarily optimized population can precipitate larger amounts of CaCO3 during the bloom in more acidified seawater, depending on parameter values. These findings suggest that ocean acidification may enhance the calcification rates of marine organisms as an adaptive response, possibly accompanied by higher carbon fixation ability. Our theory also provides a compelling explanation for the multispecific fossil time-series record from ∼200 years ago to present, in which mean coccolith size has increased along with rising atmospheric CO2 concentration.
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