Data from: Bolstered physical defences under nutrient-enriched conditions may facilitate a secondary foundational algal species in the South Pacific

1. Humans have a long history of changing species’ ranges and habitat distributions, making studies of the ecological processes that may facilitate these changes of key importance, particularly in cases where a primary foundation species is replaced by another, less desirable species. 2. We investigated the impact of nutrients and herbivory on Turbinaria ornata, a secondary foundational macroalga that depends on and likely competes with coral, the primary foundational community. T. ornata is also rapidly expanding in range and habitat across the South Pacific. We conducted: 1) a mesocosm experiment assessing relative nutrient limitation, 2) a field experiment comparing importance of nutrients (+/-) and herbivory (+/-) to biomass accumulation, and 3) an herbivory assay and toughness test comparing enriched and ambient thalli to assess changes to anti-herbivory defences. 3. We found no evidence of growth being nutrient limited in T. ornata; rather than stimulating growth, nutrient addition deterred herbivores. However, when physical toughness was removed, enriched algae were preferred, with consumption rates 25-fold those of unenriched algae. Additionally, enriched thalli were tougher than ambient thalli, suggesting physical defences were bolstered by nutrient enrichment. 4. Synthesis. We found a unique interaction where nutrients inhibit herbivory and facilitate Turbinaria ornata biomass accumulation. While concern is often placed on degradation of foundation species via anthropogenic change, instead here we show that anthropogenic change can facilitate secondary foundation species. This facilitation may allow a secondary foundation species to better compete with primary foundation species.1. 人类长期以来一直在改变物种的分布范围与栖息地格局，因此探究可推动此类变化的生态过程具有关键意义，尤其是当原生建群种（foundation species）被另一类更不受欢迎的物种所取代时。2. 本研究探究了营养盐与植食作用对团扇藻（Turbinaria ornata）的影响——团扇藻是一类依附且可能与珊瑚（原生建群群落）产生竞争的次生建群大型藻类，其分布范围与栖息地在南太平洋正快速扩张。我们开展了三项实验：1）评估相对营养盐限制的中宇宙实验；2）对比营养盐（±处理）与植食作用（±处理）对生物量积累影响程度的野外实验；3）对比营养富集组与自然环境组藻体的植食性测定与韧性测试，以探究抗植食防御机制的变化。3. 研究结果显示，团扇藻的生长并未受到营养盐限制；营养盐添加非但未促进其生长，反而抑制了植食者的取食。不过当去除物理韧性屏障后，营养富集组的藻体更受植食者偏好，其摄食率是自然环境组的25倍。此外，营养富集组的藻体韧性强于自然环境组，表明营养盐富集可增强其物理防御能力。4. 综合结论：本研究揭示了一种独特的交互作用——营养盐可抑制植食作用并促进团扇藻的生物量积累。当前学界普遍关注人为活动导致的建群种退化，而本研究则表明，人为活动带来的环境变化反而可能助力次生建群物种的扩张，这或许能使次生建群种更有效地与原生建群种展开竞争。