Department of Marine Biology and Ecology, Rosenstiel School of Marine and Atmospheric Science, University of Miami Miami, FL, USA.
Front Microbiol. 2014 Aug 4;5:400. doi: 10.3389/fmicb.2014.00400. eCollection 2014.
The performance and function of reef corals depends on the genetic identity of their symbiotic algal partners, with some symbionts providing greater benefits (e.g., photosynthate, thermotolerance) than others. However, these interaction outcomes may also depend on partner abundance, with differences in the total number of symbionts changing the net benefit to the coral host, depending on the particular environmental conditions. We suggest that symbiont abundance is a fundamental aspect of the dynamic interface between reef corals and the abiotic environment that ultimately determines the benefits, costs, and functional responses of these symbioses. This density-dependent framework suggests that corals may regulate the size of their symbiont pool to match microhabitat-specific optima, which may contribute to the high spatiotemporal variability in symbiont abundance observed within and among colonies and reefs. Differences in symbiont standing stock may subsequently explain variation in energetics, growth, reproduction, and stress susceptibility, and may mediate the impacts of environmental change on these outcomes. However, the importance of symbiont abundance has received relatively little recognition, possibly because commonly-used metrics based on surface area (e.g., symbiont cells cm(-2)) may be only weakly linked to biological phenomena and are difficult to compare across studies. We suggest that normalizing symbionts to biological host parameters, such as units of protein or numbers of host cells, will more clearly elucidate the functional role of symbiont abundance in reef coral symbioses. In this article, we generate testable hypotheses regarding the importance of symbiont abundance by first discussing different metrics and their potential links to symbiosis performance and breakdown, and then describing how natural variability and dynamics of symbiont communities may help explain ecological patterns on coral reefs and predict responses to environmental change.
珊瑚的表现和功能取决于其共生藻类伙伴的遗传身份，一些共生体比其他共生体提供更大的益处（例如，光合作用产物、耐热性）。然而，这些相互作用的结果也可能取决于伙伴的丰度，共生体的总数差异会改变对珊瑚宿主的净收益，这取决于特定的环境条件。我们认为，共生体丰度是珊瑚与非生物环境之间动态界面的一个基本方面，最终决定了这些共生关系的利益、成本和功能反应。这种密度依赖的框架表明，珊瑚可能会调节其共生体库的大小，以匹配特定小生境的最佳状态，这可能有助于解释在珊瑚个体、群体和珊瑚礁内共生体丰度的高时空变异性。共生体存量的差异随后可能解释了能量学、生长、繁殖和应激易感性的变化，并可能介导环境变化对这些结果的影响。然而，共生体丰度的重要性相对较少受到关注，这可能是因为基于表面积的常用指标（例如，共生体细胞 cm(-2)）可能与生物学现象的联系较弱，并且难以在不同研究中进行比较。我们建议，将共生体归一化为生物宿主参数，如单位蛋白质或宿主细胞数量，将更清楚地阐明共生体丰度在珊瑚共生关系中的功能作用。在本文中，我们首先讨论了不同的指标及其与共生体表现和崩溃的潜在联系，然后描述了共生体群落的自然变异性和动态如何有助于解释珊瑚礁上的生态模式，并预测对环境变化的反应，从而提出关于共生体丰度重要性的可检验假设。
