Bleaching of Symbiotic Algae (Zooxanthellae) and their Invertebrate Hosts: Causes and Mechanisms

珊瑚礁珊瑚和其他无脊椎动物的白化，即共生鞭毛藻（以下简称虫黄藻）色素的丧失，已成为热带海洋生态系统中的一个世界性问题，一些研究人员将其与全球变暖联系起来。白化的结果可能对加勒比、印度洋、太平洋和其他热带海洋地区的环境、生态和经济造成破坏性影响。虽然有一些实验工作表明高于平均温度和光照的参与，但涉及漂白的机制尚不清楚，该项目将测试三个假设。1. 自然界中的漂白是由高温胁迫加上高能蓝光（可能还有380-400nm之间的UV-A）引起的。初步证据显示，虽然高温本身会诱发白化，但在高温处理过程中，自然光照射会降低特定温度下的温度阈值和漂白时间，从而加剧白化的影响。这项研究将确定光的哪一种成分是造成这种效果和作用机制的原因。关于白化的早期理论认为光起着主要作用，但实验证据尚未支持这一论点。与高能量波长的蓝光（可能还有一些接近蓝色波长的UV-A，它们不被珊瑚中发现的防紫外线色素所吸收）相关的潜在有害化学变化，不仅与漂白的实地观察相一致，但也得到了实验室和实地初步实验的支持。2. 温度-光诱导白化的机制涉及叶绿体中叶绿素-蛋白质关联的不可逆解离。高温和光照对藻类的有害影响包括叶绿体中与反应中心相关的叶绿素-蛋白质复合物的不可逆分离或失活。电子传递活性和最终的碳固定显著降低。3. 强光和高温会导致吸收紫外线的“保护性”色素减少。本文将确定不同波长的光与高温在确定紫外线屏蔽色素浓度中的作用及其与光合速率的关系。这些假设将在实验室和现场实验中使用培养的和新鲜分离的虫黄藻以及完整的宿主进行测试。

Bleaching, the loss of symbiotic dinoflagellates)="zooxanthellae" hereafter) of their pigments, of reef corals and other invertebrates has become a world-wide problem in tropical marine ecosystem, linked by some researchers to global warming. The results of bleaching have potentially devastating environmental, ecological and economic effects in the Caribbean, IndoPacific, an other tropical marine areas. Though there is some experimental work showing involvement of both higher than average temperature and light, the mechanisms involved in bleaching are not well understood this project will test three hypotheses. 1. Bleaching in nature is caused by high temperature stress coupled with high energy blue light (and possibly UV-A between 380-400nm). Preliminary evidence shows that while high temperature alone will induce bleaching, natural light exposure during high temperature treatment exacerbates the effect by lowering the temperature threshold and time to bleaching at a given temperature. this study will determine which component of light is responsible for this effect and the mechanisms of action. Early theories on bleaching had light playing a major role, but experimental evidence has not yet supported this contention. Potentially harmful chemical alterations associated with high energy wavelengths of blue light (and possibly some near-blue wavelengths of UV-A, that are not adsorbed by UV-protecting pigments found in corals) are not only consistent with field observations of bleaching, but are also supported by both laboratory and field-based preliminary experiments. 2. The mechanisms of temperature-light induced bleaching involves the irreversible dissociation of the chlorophyll-protein associations in the chloroplast. The harmful effects of high temperatures and light on algae include the irreversible separation or inactivation of the chlorophyll-protein complexes associated with reaction centers in the chloroplast. Electron transport activity and eventually carbon fixation decrease markedly. 3. High light and temperatures cause decreases in "protective" pigments which absorb ultraviolet light. The role of different wavelengths of light in conjunction with high temperature in determining concentrations of UV-screening pigments will be determined as well as their relationship with photosynthetic rates. These hypotheses will be tested using cultured and freshly isolated zooxanthellae, and intact hosts both in the laboratory and in field-based experiments.