Host pigments of hermatypic corals as indicators of environmental stress in reef communities

浅水珊瑚礁是海洋生物多样性最重要的中心之一，提供宝贵的生态系统服务，因为数百万人在经济上依赖珊瑚礁及其生物。全球变暖、海洋酸化、污染加剧、过度捕捞、捕食者或病原体的攻击、盐度变化和沉积物增加等多种自然和人为压力因素可能导致珊瑚礁在本世纪内急剧消失。珊瑚礁的未来在很大程度上取决于能够确定受高度压力影响的珊瑚礁区域和预测白化事件的战略，以便加强对特别脆弱地区的管理工作。然而，目前可用的遥感技术的预测能力是有限的，这是因为预测主要是基于温度异常，并没有考虑到上述众多的压力因素，共同作用，以增加漂白的敏感性。因此，需要采取的办法是分析珊瑚本身的累积反应，而不是单一的环境参数。最近，我们发现，基因编码的代表家庭的GFP（绿色荧光蛋白）样蛋白质的差异调节应激反应。这些色素是造礁珊瑚大部分强烈的紫蓝色、绿色或红色色调的原因。该蛋白质家族的荧光代表在用合适波长的光刺激时发射从青色到红色的光谱范围内的光子。我们可以表明，由于热应激，FP转录水平强烈降低，但在寒冷和氧化应激下增加。珊瑚中FP基因对环境条件的各种变化的强烈反应表明，这些色素可能是珊瑚健康迫切需要的内在标志。指示样本的荧光特征的光谱分析可以允许一个非侵入性的，快速和低成本的方法来评估珊瑚礁群落的压力水平。事实上，激光荧光成像作为获取珊瑚礁大面积区域珊瑚荧光提供的信息的潜在工具，在技术上是可行的。然而，需要详细了解珊瑚色素对环境变化的反应的特殊性和重要性，以确定珊瑚颜色是珊瑚健康的累积指标。目前，尚不清楚从短期（小时）实验中报告的FP转录物的下调是否也导致蛋白质水平的可测量的降低。这并不是一个不言自明的结果，因为我们以前发现珊瑚组织中的蛋白质色素周转缓慢（半衰期约为3周），这可能会掩盖转录水平的短期变化。拟议的研究将侧重于温度压力作为珊瑚礁的一个突出威胁。此外，检查这种应激因子对宿主色素的组织含量的影响最有希望证明新监测概念的原理证明，因为在短期实验中已经观察到编码GFP样蛋白的转录物的下调。我们的研究结果将极大地促进未来的实验，将测试珊瑚对不同形式的压力组合的反应，并完善基于荧光蛋白的生物指示剂系统，以允许不同的生理反应之间的歧视。

Shallow water coral reefs are among the most important centres of marine biodiversity providing invaluable ecosystem services as millions of people are economically dependent on the reef and its creatures. A multiplicity of natural and anthropogenic stressors such as global warming, ocean acidification, rising pollution, overfishing, attacks by predators or pathogens, salinity variations and increased sedimentation might result in a dramatic loss of coral reefs within this century. The future of coral reefs is strongly dependent on strategies that enable identification of reef regions affected by high levels of stress and to forecast bleaching events in order to enhance management efforts on particularly vulnerable areas. However, the predictive capacity of currently available remote sensing techniques is limited by the fact that prediction is mainly based on temperature anomalies and does not consider the above mentioned multitude of stress factors that act together to increase susceptibility to bleaching. Consequently, approaches are required that analyse the cumulative response of corals themselves rather than single environmental parameters. Most recently, we showed that genes encoding representatives of the family of GFP (green fluorescent protein)-like proteins were differentially regulated in response to stress. These pigments are responsible for most of the intense purple-blue, green, or reddish hues of reef-building corals. Fluorescent representatives of this protein family emit photons in the spectral range from cyan to red upon stimulation with light of suitable wavelengths. We could show that FP transcript levels were strongly reduced due to heat stress, but increased under cold and oxidative stress. The strong response of FP genes in corals to various changes of the environmental conditions suggests that these pigments might serve as the urgently needed intrinsic markers of coral health. The spectral analysis of fluorescence signatures of indicator specimens could allow a non-invasive, fast and low cost method to assess stress levels in coral reef communities. Indeed, laser fluorescence imaging as potential tool to access the information provided by coral fluorescence in large spatial areas of coral reefs was shown to be technically feasible. However, detailed knowledge about the specificity and significance of the response of coral pigments to environmental changes is required to establish coral colour as a cumulative indicator of coral health. At present, it is not clear if the downregulation of FP transcripts reported from short term (hours) experiments results also in a measurable reduction of protein levels. This is not a self-evident consequence, as we found previously that the proteins pigments in coral tissue have a slow turnover (half-life ~3 weeks) that might mask short-term alterations at the transcript level. The proposed study will focus on temperature stress as an eminent threat for coral reefs. Moreover, examination of the effect of this stress factor on the tissue content of host pigments is most promising to demonstrate the proof of principle of the new monitoring concept as a downregulation of transcripts encoding GFP-like proteins was already observed in short term experiments. Our results will greatly facilitate future experiments that will test the reponse of corals to combinations of different forms of stress and refine the fluorescent protein-based bioindicator system to allow for the discrimination among different physiological responses.