Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, 27568 Bremerhaven, Germany; Department of Biology and Chemistry, University of Bremen, 28359 Bremen, Germany; Marine Biological Section, Department of Biology, University of Copenhagen, 3000 Helsingør, Denmark.
Max Planck Institute for Marine Microbiology, 28359 Bremen, Germany; MARUM - Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany.
Curr Biol. 2022 Oct 10;32(19):4150-4158.e3. doi: 10.1016/j.cub.2022.07.071. Epub 2022 Aug 23.
Most tropical corals live in symbiosis with Symbiodiniaceae algae whose photosynthetic production of oxygen (O) may lead to excess O in the diffusive boundary layer (DBL) above the coral surface. When flow is low, cilia-induced mixing of the coral DBL is vital to remove excess O and prevent oxidative stress that may lead to coral bleaching and mortality. Here, we combined particle image velocimetry using O-sensitive nanoparticles (sensPIV) with chlorophyll (Chla)-sensitive hyperspectral imaging to visualize the microscale distribution and dynamics of ciliary flows and O in the coral DBL in relation to the distribution of Symbiodiniaceae Chla in the tissue of the reef building coral, Porites lutea. Curiously, we found an inverse relation between O in the DBL and Chla in the underlying tissue, with patches of high O in the DBL above low Chla in the underlying tissue surrounding the polyp mouth areas and pockets of low O concentrations in the DBL above high Chla in the coenosarc tissue connecting neighboring polyps. The spatial segregation of Chla and O is related to ciliary-induced flows, causing a lateral redistribution of O in the DBL. In a 2D transport-reaction model of the coral DBL, we show that the enhanced O transport allocates parts of the O surplus to areas containing less chla, which minimizes oxidative stress. Cilary flows thus confer a spatially complex mass transfer in the coral DBL, which may play an important role in mitigating oxidative stress and bleaching in corals.
大多数热带珊瑚与共生的 Symbiodiniaceae 藻类生活在一起，藻类的光合作用会产生氧气 (O)，这可能导致珊瑚表面上方的扩散边界层 (DBL) 中氧气过剩。当水流较低时，纤毛诱导的珊瑚 DBL 混合对于去除多余的 O 和防止可能导致珊瑚白化和死亡的氧化应激至关重要。在这里，我们结合使用对氧气敏感的纳米粒子的粒子图像测速 (sensPIV) 和对叶绿素 (Chla) 敏感的高光谱成像，可视化纤毛流和 O 在珊瑚 DBL 中的微尺度分布和动力学，以及共生藻 Chla 在造礁珊瑚组织中的分布，Porites lutea。奇怪的是，我们发现 DBL 中的 O 和下方组织中的 Chla 之间存在反比关系，在息肉口区域周围的下方组织中 DBL 中存在高 O 斑块，而在相邻息肉连接的 coenosarc 组织中 DBL 中存在高 Chla 斑块上方存在低 O 浓度。Chla 和 O 的空间分离与纤毛诱导的流动有关，导致 DBL 中的 O 发生横向再分配。在珊瑚 DBL 的二维传输-反应模型中，我们表明增强的 O 传输将部分 O 盈余分配到含 chla 较少的区域，从而将氧化应激最小化。因此，纤毛流在珊瑚 DBL 中赋予了复杂的空间传质，这可能在减轻珊瑚的氧化应激和白化方面发挥重要作用。
