We characterized the planular-zooxanthellae symbiosis of the coral Pocillopora damicornis using criteria that are familiar in studies on corals. Similar to adult corals, planulae exhibited photoacclimation, as changes in symbiont chlorophyll a (chl a); changes in the light-saturation constant for photosynthesis (I(k)); and, at insufficient light, fewer zooxanthellae, decreased respiration, increased weight loss, and increased sensitivity to photoinhibition. Numbers of zooxanthellae in newly-released planulae varied by at least three-fold within broods. Planulae with low versus high numbers of zooxanthellae (termed pale versus dark planulae, respectively) did not differ in symbiont chl-a content, I(k), or biomass-specific rate of dark respiration. Pale planulae had lower rates of photosynthesis, but this difference vanished after three weeks, when zooxanthellar numbers increased by 225% in pale planulae and by 31% in dark planulae. Numbers of zooxanthellae also increased significantly in planulae cultured in ammonium-enriched seawater; ammonium also apparently prevented weight loss and induced settlement. Approximately 70% of photosynthetically-fixed carbon (labeled using (14)C) apparently was translocated from the zooxanthellae to their host. A comparison of planulae cultured at 0.3% versus 11% sunlight suggested that photosynthesis provided ~ 31% of the energy utilized by the latter. Overall, we conclude that the physiology of symbiosis in planulae of P. damicornis is broadly similar to symbiosis physiology in adult corals.

中文翻译：

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珊瑚 Pocillopora damicornis 浮游幼虫中的虫黄藻共生

我们使用珊瑚研究中熟悉的标准对珊瑚 Pocillopora damicornis 的平面-虫黄藻共生进行了表征。与成年珊瑚相似，浮游珊瑚表现出光驯化，作为共生体叶绿素 a (chl a) 的变化；光合作用光饱和常数的变化 (I(k))；并且，在光照不足的情况下，虫黄藻较少，呼吸减少，体重减轻增加，对光抑制的敏感性增加。新释放的浮游生物中虫黄藻的数量在育雏内变化至少三倍。虫黄藻数量较少与数量较多的浮游藻（分别称为苍白浮游藻和深色浮游藻）在共生体 chl-a 含量、I(k) 或生物量特定的暗呼吸速率方面没有差异。苍白的平原有较低的光合作用速率，但这种差异在三周后消失了，当苍白的扁平藻中虫黄藻数量增加了 225%，而黑暗扁平藻中的虫黄藻数量增加了 31%。在富铵海水中培养的浮游生物中，虫黄藻的数量也显着增加；铵也明显地防止了重量减轻和诱导沉降。大约 70% 的光合作用固定碳（用（14）​​C 标记）显然从虫黄藻转移到它们的宿主。在 0.3% 与 11% 阳光下培养的浮游生物的比较表明，光合作用提供了后者所利用能量的约 31%。总体而言，我们得出结论，P. damicornis 扁平藻中的共生生理学与成年珊瑚的共生生理学大致相似。在富铵海水中培养的浮游生物中，虫黄藻的数量也显着增加；铵也明显地防止了重量减轻和诱导沉降。大约 70% 的光合作用固定碳（用（14）​​C 标记）显然从虫黄藻转移到它们的宿主。在 0.3% 与 11% 阳光下培养的浮游生物的比较表明，光合作用提供了后者所利用能量的约 31%。总体而言，我们得出结论，P. damicornis 扁平藻中的共生生理学与成年珊瑚的共生生理学大致相似。在富铵海水中培养的浮游生物中，虫黄藻的数量也显着增加；铵也明显地防止了重量减轻和诱导沉降。大约 70% 的光合作用固定碳（用（14）​​C 标记）显然从虫黄藻转移到它们的宿主。在 0.3% 与 11% 阳光下培养的浮游生物的比较表明，光合作用提供了后者所利用能量的约 31%。总体而言，我们得出结论，P. damicornis 扁平藻中的共生生理学与成年珊瑚的共生生理学大致相似。在 0.3% 与 11% 阳光下培养的浮游生物的比较表明，光合作用提供了后者所利用能量的约 31%。总体而言，我们得出结论，P. damicornis 扁平藻中的共生生理学与成年珊瑚的共生生理学大致相似。在 0.3% 与 11% 阳光下培养的浮游生物的比较表明，光合作用提供了后者所利用能量的约 31%。总体而言，我们得出结论，P. damicornis 扁平藻中的共生生理学与成年珊瑚的共生生理学大致相似。