Department of Marine Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599-3300, USA.
Department of Biology, Boston University, 5 Cummington Mall, Boston, MA, 02215, USA.
Microb Ecol. 2018 May;75(4):903-915. doi: 10.1007/s00248-017-1096-6. Epub 2017 Nov 2.
Reef-building corals maintain a symbiotic relationship with dinoflagellate algae of the genus Symbiodinium, and this symbiosis is vital for the survival of the coral holobiont. Symbiodinium community composition within the coral host has been shown to influence a coral's ability to resist and recover from stress. A multitude of stressors including ocean warming, ocean acidification, and eutrophication have been linked to global scale decline in coral health and cover in recent decades. Three distinct thermal regimes (high, mod, and low) following an inshore-offshore gradient of declining average temperatures and thermal variation were identified on the Belize Mesoamerican Barrier Reef System (MBRS). Quantitative metabarcoding of the ITS-2 locus was employed to investigate differences and similarities in Symbiodinium genetic diversity of the Caribbean corals Siderastrea siderea, S. radians, and Pseudodiploria strigosa between the three thermal regimes. A total of ten Symbiodinium lineages were identified across the three coral host species. S. siderea was associated with distinct Symbiodinium communities; however, Symbiodinium communities of its congener, S. radians and P. strigosa, were more similar to one another. Thermal regime played a role in defining Symbiodinium communities in S. siderea but not S. radians or P. strigosa. Against expectations, Symbiodinium trenchii, a symbiont known to confer thermal tolerance, was dominant only in S. siderea at one sampled offshore site and was rare inshore, suggesting that coral thermal tolerance in more thermally variable inshore habitats is achieved through alternative mechanisms. Overall, thermal parameters alone were likely not the only primary drivers of Symbiodinium community composition, suggesting that environmental variables unrelated to temperature (i.e., light availability or nutrients) may play key roles in structuring coral-algal communities in Belize and that the relative importance of these environmental variables may vary by coral host species.
造礁石珊瑚与共生的虫黄藻属（Symbiodinium）藻类维持共生关系，这种共生关系对珊瑚整体的生存至关重要。珊瑚宿主中的共生体群落组成被证明会影响珊瑚抵抗和从压力中恢复的能力。近年来，许多压力源，包括海洋变暖、海洋酸化和富营养化，与全球范围内珊瑚健康和覆盖范围的下降有关。在伯利兹中美洲堡礁系统（MBRS），根据从近岸到近海的温度降低和温度变化梯度，确定了三个不同的热区（高温、中温和低温）。采用 ITS-2 基因座的定量代谢条码技术，研究了三种热区加勒比珊瑚石珊瑚（Siderastrea siderea、S. radians 和 Pseudodiploria strigosa）中共生藻遗传多样性的差异和相似性。在这三种珊瑚宿主中，共鉴定出十种共生藻谱系。S. siderea 与独特的共生藻群落相关；然而，其近缘种 S. radians 和 P. strigosa 的共生藻群落彼此更为相似。热区在 S. siderea 中对共生藻群落的形成起作用，但在 S. radians 和 P. strigosa 中不起作用。出乎意料的是，已知具有耐热性的共生藻 Symbiodinium trenchii 仅在一个采样的近海地点的 S. siderea 中占优势，在近岸地区则很少见，这表明在温度变化较大的近岸生境中，珊瑚的耐热性是通过其他机制实现的。总体而言，仅热参数可能不是共生藻群落组成的唯一主要驱动因素，这表明与温度无关的环境变量（即光照可用性或营养物质）可能在伯利兹珊瑚-藻类群落的结构中发挥关键作用，并且这些环境变量的相对重要性可能因珊瑚宿主物种而异。
