Department of Geography and the Environment, Villanova University, 800 E Lancaster Ave., Villanova, PA 19085, USA.
School of Aquatic and Fishery Sciences, University of Washington, 1122 NE Boat St., Seattle, WA 98105, USA.
Proc Biol Sci. 2024 Feb 28;291(2017):20231534. doi: 10.1098/rspb.2023.1534. Epub 2024 Feb 21.
In mesophotic coral ecosystems, reef-building corals and their photosynthetic symbionts can survive with less than 1% of surface irradiance. How depth-specialist corals rely upon autotrophically and heterotrophically derived energy sources across the mesophotic zone remains unclear. We analysed the stable carbon (C) and nitrogen (N) isotope values of a community from the 'Au'au Channel, Maui, Hawai'i (65-125 m) including four coral host species living symbiotically with three algal haplotypes. We characterized the isotope values of hosts and symbionts across species and depth to compare trophic strategies. Symbiont C was consistently 0.5‰ higher than host C at all depths. Mean colony host and symbiont N differed by up to 3.7‰ at shallow depths and converged at deeper depths. These results suggest that both heterotrophy and autotrophy remained integral to colony survival across depth. The increasing similarity between host and symbiont N at deeper depths suggests that nitrogen is more efficiently shared between mesophotic coral hosts and their algal symbionts to sustain autotrophy. Isotopic trends across depth did not generally vary by host species or algal haplotype, suggesting that photosynthesis remains essential to survival and growth despite low light availability in the mesophotic zone.
在中层珊瑚生态系统中，造礁珊瑚及其共生光合作用生物可以在不到表面光照的 1%的情况下存活。在中层带，深度专化珊瑚如何依赖自养和异养来源的能量仍然不清楚。我们分析了来自夏威夷毛伊岛 'Au'au 海峡（65-125 米）的一个群落的稳定碳（C）和氮（N）同位素值，该群落包括四种与三种藻类单倍型共生的珊瑚宿主物种。我们描述了宿主和共生体在不同物种和深度下的同位素值，以比较它们的营养策略。在所有深度下，共生体的 C 始终比宿主的 C 高 0.5‰。在浅层，菌落宿主和共生体的 N 差异最大可达 3.7‰，而在较深的深度上趋同。这些结果表明，在整个深度范围内，异养和自养对菌落的生存都是必不可少的。在更深的深度，宿主和共生体的 N 之间的相似性增加，表明氮在中层珊瑚宿主与其藻类共生体之间的共享效率更高，从而维持了自养。跨深度的同位素趋势通常不受宿主物种或藻类单倍型的影响，这表明尽管中层带光照不足，光合作用仍然是生存和生长的关键。
