Seagrasses are important foundational species that frequently display distinct depth distributions, although the drivers of these patterns can be spatially and temporally variable. While the pantropical seagrass Halophila decipiens is known from waters as shallow as 1 m deep, in Moorea, French Polynesia we only found it > 6.4 m deep. To explore factors affecting depth distribution, we transplanted H. decipiens into 3 habitats: the existing seagrass bed (control), just outside the seagrass bed, and shallower habitat adjacent to a fringing coral reef. Results showed that growth was not significantly different between the control and just outside of the seagrass bed; however, number of shoots and rhizome length were significantly reduced adjacent to the reef. Transplanting seagrass into the shallow reef site with and without herbivore exclusion cages showed that H. decipiens grew in herbivore exclusion treatments, but lost both shoots and rhizomes in the control. These results indicate that H. decipiens can grow in shallow habitats adjacent to reefs on Moorea, but that herbivory pressure, presumably from the reef, limits its depth distribution.

海草是经常显示不同深度分布的重要基础物种，尽管这些模式的驱动因素可能在空间和时间上是可变的。虽然从浅至1 m深的水域中已知泛热带海草Halophila decipiens，但在法属波利尼西亚的Moorea，我们仅发现其深> 6.4 m。为了探索影响深度分布的因素，我们移植了H. decipiens分为3个栖息地：现有的海草床（对照），就在海草床的外面，以及与边缘珊瑚礁相邻的较浅的栖息地。结果表明，对照组与海草床外之间的生长没有显着差异。然而，靠近礁石的枝条数量和根茎长度明显减少。将海草移植到有或没有草食动物隔离笼的浅礁区表明，在草食动物隔离处理中，纤毛藻生长，但在对照中失去了枝条和根茎。这些结果表明，H。decipiens可以生长在Moorea上与礁石相邻的浅层栖息地中，但据推测来自礁石的食草压力限制了其深度分布。