Herbivory and nutrient availability are fundamental drivers of benthic community succession in shallow marine systems, including coral reefs. Despite the importance of early community succession for coral recruitment and recovery, studies characterizing the impact of top-down and bottom-up drivers on micro- and macrobenthic communities at scales relevant to coral recruitment are lacking. Here, a combination of tank and field experiments were used to assess the effects of herbivore exclusion and nutrient enrichment on micro- to macrobenthic community succession and subsequent coral recruitment success. Herbivore exclusion had the strongest effect on micro- and macrobenthic community succession, including a community shift toward copiotrophic and potentially opportunistic/pathogenic microorganisms, an increased cover of turf and macroalgae, and decreased cover of crustose coralline algae. Yet, when corals settled prior to the development of a macrobenthic community, rates of post-settlement survival increased when herbivores were excluded, benefiting from the predation refugia provided by cages during their vulnerable early post-settlement stage. Interestingly, survival on open tiles was negatively correlated with the relative abundance of the bacterial order Rhodobacterales, an opportunistic microbial group previously associated with stressed and diseased corals. Development of micro- and macrobenthic communities in the absence of herbivory, however, led to reduced coral settlement. In turn, there were no differences in post-settlement survival between open and caged treatments for corals settled on tiles with established benthic communities. As a result, open tiles experienced marginally higher recruitment rates, driven primarily by the higher initial number of settlers on open tiles compared to caged tiles. Overall, we reveal that the primary interaction driving coral recruitment is the positive effect of herbivory in creating crustose coralline algae (CCA)-dominated habitats, free of fleshy algae and associated opportunistic microbes, to enhance coral settlement. The negative direct and indirect impact of fish predation on newly settled corals was outweighed by the positive effect of herbivory on the initial rate of coral settlement. In turn, the addition of nutrients further altered benthic community succession in the absence of herbivory, reducing coral post-settlement survival. However, the overall impact of nutrients on coral recruitment dynamics was minor relative to herbivory.

中文翻译：

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过度捕捞和营养丰富下的底栖微型和宏观群落演替和珊瑚补充

食草和养分供应是浅海系统（包括珊瑚礁）中底栖群落演替的基本驱动因素。尽管早期群落演替对珊瑚的补充和恢复很重要，但缺乏表征自上而下和自下而上的驱动因素在与珊瑚补充相关的尺度上对微型和大型底栖动物群落的影响的研究。在这里，水箱和田间实验的组合被用来评估食草动物排斥和营养丰富对微型到大型底栖动物群落演替和随后珊瑚补充成功的影响。草食动物排斥对微型和大型底栖动物群落演替的影响最大，包括群落向营养型和潜在的机会性/病原微生物转变，草皮和大型藻类的覆盖增加，和减少壳状珊瑚藻的覆盖。然而，当珊瑚在大型底栖动物群落发展之前定居时，当食草动物被排除在外时，定居后的存活率会增加，这得益于笼子在定居后早期脆弱的早期阶段提供的捕食避难所。有趣的是，开放瓷砖上的存活率与细菌顺序的相对丰度呈负相关红杆菌目，以前与压力和患病珊瑚相关的机会主义微生物群。然而，在没有食草动物的情况下，微型和大型底栖动物群落的发展导致珊瑚沉降减少。反过来，对于定居在具有已建立底栖群落的瓷砖上的珊瑚，开放式和笼式处理之间的定居后存活率没有差异。因此，开放式瓷砖的招聘率略高，这主要是由于与笼式瓷砖相比，开放式瓷砖上的初始定居者人数更多。总体而言，我们揭示了驱动珊瑚补充的主要相互作用是食草动物在创造以硬壳珊瑚藻（CCA）为主的栖息地的积极影响，没有肉质藻类和相关的机会性微生物，以增强珊瑚沉降。鱼类捕食对新定居珊瑚的负面直接和间接影响被食草动物对珊瑚初始沉降率的积极影响所抵消。反过来，在没有食草动物的情况下，营养物质的添加进一步改变了底栖群落的演替，从而降低了珊瑚定居后的存活率。然而，相对于食草动物，养分对珊瑚补充动态的总体影响较小。