Abstract：
Most tropical corals live in symbiosis with Symbiodiniaceae algae whose photosynthetic production of oxygen (O2) may lead to excess O2 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 O2 and prevent oxidative stress that may lead to coral bleaching and mortality. Here, we combined particle image velocimetry using O2-sensitive nanoparticles (sensPIV) with chlorophyll (Chla)-sensitive hyperspectral imaging to visualize the microscale distribution and dynamics of ciliary flows and O2 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 O2 in the DBL and Chla in the underlying tissue, with patches of high O2 in the DBL above low Chla in the underlying tissue surrounding the polyp mouth areas and pockets of low O2 concentrations in the DBL above high Chla in the coenosarc tissue connecting neighboring polyps. The spatial segregation of Chla and O2 is related to ciliary-induced flows, causing a lateral redistribution of O2 in the DBL. In a 2D transport-reaction model of the coral DBL, we show that the enhanced O2 transport allocates parts of the O2 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.
摘要：
大多数热带珊瑚与共生科藻类共生，其光合作用产生的氧气（O2）可能导致珊瑚表面上方的扩散边界层（DBL）中过量的O2。当流量较低时，纤毛诱导的珊瑚DBL混合对于去除过量的O2和防止可能导致珊瑚漂白和死亡的氧化应激至关重要。这里,我们将使用O2敏感纳米粒子（sensPIV）的粒子图像测速与叶绿素（Chla）敏感的高光谱成像相结合，以可视化珊瑚DBL中纤毛流和O2的微观分布和动力学，与共生菌科Chla的分布有关的珊瑚礁建设珊瑚的组织，Poriteslutea.奇怪的是,我们发现DBL中的O2和下层组织中的Chla之间存在反比关系，在息肉口区域周围的下层组织中，DBL中的高O2高于低Chla，而在连接相邻息肉的coenosarc组织中，DBL中的低O2浓度高于高Chla。Chla和O2的空间分离与纤毛引起的流动有关，导致DBL中O2的横向重新分布。在珊瑚DBL的2D传输反应模型中，我们表明，增强的O2传输将部分O2过剩分配给含有较少chla的区域，最大限度地减少氧化应激。纤毛流在珊瑚DBL中赋予空间复杂的传质，这可能在减轻珊瑚的氧化应激和漂白中起重要作用。
