Seagrasses cope with excess irradiance using a suit of photoprotective mechanisms, however, Halophila species are the only seagrasses known to exhibit chloroplast avoidance movement. Here we examined this phenomenon together with concurrent change in photosynthetic and leaf optical properties in H. ovalis and H. decipiens. Although co-existing, these two seagrasses displayed different light use characteristics derived from rapid light curves; H. ovalis and H. decipiens showed features of sun- and shade-adapted plants, respectively. Experimentally the seagrass leaves were exposed to low, medium, and high irradiance (80, 200 and 800 μmol photons m⁻² s⁻¹, respectively) for 60 min, followed by 60 min in darkness. Chloroplast movement occurred in H. ovalis exposed to medium or high irradiance and in H. decipiens exposed to low or medium irradiance. Chloroplast gathering was observed after 20 min of exposure and chloroplast dispersal was observed after 20 min in darkness, dependent on treatment and species. Increasing irradiance lowered the effective quantum yield and increased the non-photochemical quenching (NPQ). Despite stronger up-regulation in NPQ, photoinhibition was detected in H. decipiens. The absorption factor and the Soil-Plant Analysis Development value were modulated by chloroplast movement rather than a change in chlorophyll content, except for H. decipiens exposed to high irradiance where photodamage of chlorophylls may have occurred. Chloroplast movement in both seagrasses was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea, indicating regulation by photosynthesis. Our results suggest that H. ovalis has a higher tolerance to excess irradiance than H. decipiens and that this is assisted partly by chloroplast avoidance movement.

海草使用一套光保护机制来应对过度的辐照，但是，嗜盐菌物种是已知唯一能够避免叶绿体运动的海草。在这里，我们研究了这种现象，并同时改变了H.卵圆和H. decipiens的光合和叶片光学性质。尽管这两种海草并存，但它们显示出了从快速光曲线得出的不同的光利用特性。卵形嗜血杆菌和de形嗜血菌分别表现出适应日光和阴暗的植物特征。实验中，海草叶暴露于低，中和高辐照度（80、200和800μmol光子m ^-2 s ^-1）60分钟，然后在黑暗中60分钟。叶绿体的运动发生在暴露于中等或高辐照度的卵形H.和暴露于中等或中等辐照度的H. decipiens。取决于处理方式和种类，在暴露20分钟后观察到叶绿体聚集，在黑暗中20分钟后观察到叶绿体分散。辐照度的增加降低了有效量子产率，并增加了非光化学猝灭（NPQ）。尽管NPQ中的上调较强，但在H. decipiens中检测到了光抑制作用。吸收因子和土壤-植物分析发展值是通过叶绿体运动而不是叶绿素含量的变化来调节的，除了H. decipiens暴露于高辐照度下可能会发生叶绿素的光损伤。3-（3,4-二氯苯基）-1,1-二甲基脲抑制了两个海草中的叶绿体运动，表明其受光合作用的调节。我们的结果表明，卵形嗜血杆菌对过量辐照的耐受性高于蜕皮嗜血菌，这在一定程度上得益于避免叶绿体的运动。