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Differential resistance and acclimation of two coral species to chronic nutrient enrichment reflect life‐history traits
Functional Ecology ( IF 5.2 ) Pub Date : 2021-02-27 , DOI: 10.1111/1365-2435.13780
Michael D. Fox 1 , Craig E. Nelson 2 , Thomas A. Oliver 3 , Zachary A. Quinlan 2, 4 , Kristina Remple 2 , Jess Glanz 5 , Jennifer E. Smith 1 , Hollie M. Putnam 6
Affiliation  

  1. The effects of nutrient pollution on coral reef ecosystems are multifaceted. Numerous experiments have sought to identify the physiological effects of nutrient enrichment on reef‐building corals, but the results have been variable and sensitive to choices of nutrient quantity, chemical composition and exposure duration.
  2. To test the effects of chronic, ecologically relevant nutrient enrichment on coral growth and photophysiology, we conducted a 5‐week continuous dosing experiment on two Hawaiian coral species, Porites compressa and Pocillopora acuta. We acclimated coral fragments to five nutrient concentrations (0.1–7 µM urn:x-wiley:02698463:media:fec13780:fec13780-math-0001 and 0.06–2.24 µM urn:x-wiley:02698463:media:fec13780:fec13780-math-0002) with constant stoichiometry 2.5:1 nitrate to phosphate) bracketing in situ observations from reefs throughout the Pacific.
  3. Nutrient enrichment linearly increased photophysiological performance of both species within 3 weeks. The effect of nutrients on P. acuta photochemical efficiency increased through time while a consistent response in P. compressa indicated acclimation to elevated nutrients within 5 weeks. Endosymbiont densities and total chlorophyll concentrations also increased proportionally with nutrient enrichment in P. acuta, but not in P. compressa, revealing contrasting patterns of host–symbiont acclimatization.
  4. The two species also exhibited contrasting effects of nutrient enrichment on skeletal growth. Calcification was enhanced at low nutrient enrichment (1 µM urn:x-wiley:02698463:media:fec13780:fec13780-math-0003) in P. acuta, but comparable to the control at higher concentrations, whereas calcification was reduced in P. compressa (30%–35%) above 3 µM urn:x-wiley:02698463:media:fec13780:fec13780-math-0004.
  5. Stable isotope analysis revealed species‐specific nitrogen uptake dynamics in the coral–algal symbiosis. The endosymbionts of P. acuta exhibited increased nitrogen uptake (decreased δ15N) and incorporation (19%–31% decrease in C:N ratios) across treatments. In contrast, P. compressa endosymbionts maintained constant δ15N values and low levels of nitrogen incorporation (9%–11% decrease in C:N ratios). The inability of P. acuta to regulate endosymbiont nutrient uptake may indicate an emerging destabilization in the coral–algal symbiosis under nutrient enrichment that could compromise resistance to additional environmental stressors.
  6. Our results highlight species‐specific differences in the coral–algal symbiosis, which influence responses to chronic nutrient enrichment. These findings showcase how symbioses can vary among closely related taxa and underscore the importance of considering how life‐history traits modify species response to environmental change.


中文翻译:

两种珊瑚对慢性营养富集的差异抗性和适应性反映了生活史特征

  1. 营养物质污染对珊瑚礁生态系统的影响是多方面的。许多实验试图确定养分富集对造礁珊瑚的生理影响,但是结果是可变的,并且对养分量,化学成分和暴露时间的选择敏感。
  2. 为了测试长期的,与生态相关的营养物丰富度对珊瑚生长和光生理的影响,我们对两种夏威夷珊瑚物种(Porites compressaPocillopora acuta)进行了为期5周的连续剂量试验。我们将珊瑚碎片适应了五种营养物浓度(0.1–7 µM骨灰盒:x-wiley:02698463:media:fec13780:fec13780-math-0001和0.06–2.24 µM 骨灰盒:x-wiley:02698463:media:fec13780:fec13780-math-0002,化学计量比恒定为2.5:1硝酸盐至磷酸盐),并在整个太平洋地区的珊瑚礁进行了现场观测。
  3. 营养物富集在3周内线性增加了两个物种的光生理性能。养分对cutcut acuta光化学效率的影响随着时间的推移而增加,而在P. compressa中一致的响应表明在5周内适应了养分升高。内生共生菌密度和总叶绿素浓度也随着营养的富集而按比例增加,但在cut实假单胞菌中却没有,这表明宿主-共生适应的方式不同。
  4. 这两个物种还表现出营养丰富对骨骼生长的对比作用。营养成分低(1 µM 骨灰盒:x-wiley:02698463:media:fec13780:fec13780-math-0003)时褐藻中的钙化作用增强,但与较高浓度的对照相比,其钙化程度有所提高,而高于3 µM的压缩疟原虫(30%–35%)中的钙化作用则降低骨灰盒:x-wiley:02698463:media:fec13780:fec13780-math-0004
  5. 稳定的同位素分析揭示了珊瑚-藻类共生中特定物种的氮吸收动态。的内共生体P.蚧显示出增加的氮摄取(减小δ 15 N)和结合(19%-31%的降低在C:N比)跨越治疗。与此相反,P.牛鞭内共生体保持恒定δ 15的N值和氮引入水平低(9%-11%的降低在C:N比)。枯草假单胞菌无法调节共生菌内养分的吸收,这可能表明在养分富集下珊瑚-藻共生中出现了新的不稳定现象,这可能会损害对其他环境胁迫的抵抗力。
  6. 我们的结果强调了珊瑚-藻类共生中特定物种的差异,这影响了对长期营养物富集的反应。这些发现证明了共生关系在密切相关的类群之间如何变化,并强调了考虑生命历史特征如何改变物种对环境变化的反应的重要性。
更新日期:2021-05-07
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