Marine food webs are structured through a combination of top-down and bottom-up processes. In coral reef ecosystems, fish size is related to life-history characteristics and size-based indicators can represent the distribution and flow of energy through the food web. Thus, size spectra can be a useful tool for investigating the impacts of both fishing and habitat condition on the health and productivity of coral reef fisheries. In addition, coral reef fisheries are often data-limited and size spectra analysis can be a relatively cost-effective and simple method for assessing fish populations. Abundance size spectra are widely used and quantify the relationship between organism size and relative abundance. Previous studies that have investigated the impacts of fishing and habitat condition together on the size distribution of coral reef fishes, however, have aggregated all fishes regardless of taxonomic identity. This leads to a poor understanding of how fishes with different feeding strategies, body size-abundance relationships, or catchability might be influenced by top-down and bottom-up drivers. To address this gap, we quantified size spectra slopes of carnivorous and herbivorous coral reef fishes across three regions of Indonesia representing a gradient in fishing pressure and habitat conditions. We show that fishing pressure was the dominant driver of size spectra slopes such that they became steeper as fishing pressure increased, which was due to the removal of large-bodied fishes. When considering fish functional groups separately, however, carnivore size spectra slopes were more heavily impacted by fishing than herbivores. Also, structural complexity, which can mediate predator-prey interactions and provisioning of resources, was a relatively important driver of herbivore size spectra slopes such that slopes were shallower in more complex habitats. Our results show that size spectra slopes can be used as indicators of fishing pressure on coral reef fishes, but aggregating fish regardless of trophic identity or functional role overlooks differential impacts of fishing pressure and habitat condition on carnivore and herbivore size distributions.

中文翻译：

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钓鱼和生境条件差异影响的珊瑚礁鱼类粒径谱斜率

海洋食物网是通过自上而下和自下而上的过程的组合结构。在珊瑚礁生态系统，鱼的大小是关系到生命的历史特征和基于大小的指标可以代表的分布，并通过食物链的能量流动。因此，粒径谱可用于调查的两个捕鱼和栖息地的条件对珊瑚礁渔业的健康和生产力的影响的有用工具。此外，珊瑚礁渔业往往数据限制和大小光谱分析可以是用于评估鱼群相对成本有效且简单的方法。丰度大小光谱得到广泛使用，量化生物体的大小和相对丰度之间的关系。以前的研究已经调查珊瑚礁鱼类的大小分布一起捕捞和栖息地状况的影响，然而，无论分类身份如何，都汇总了所有鱼类。这导致了如何与不同的喂养策略，机身尺寸丰度的关系，或可捕的鱼可能会通过自上而下和自下而上的驱动的影响认识不足。为了解决这个差距，我们量化跨代表的捕捞压力和生境条件的梯度印度尼西亚三个区域食肉和食草珊瑚礁鱼类粒径谱斜率。我们发现，捕捞压力就是这样，他们成了陡峭的捕捞压力增加，这是由于去除体型大的鱼大小光谱的斜坡的主要驱动力。当单独考虑鱼的官能团，然而，肉食动物粒径谱斜率更深受钓鱼比食草动物的影响。此外，结构复杂，可介导捕食相互作用和供应资源的，是草食动物粒径谱斜率的相对重要的驱动器，使得斜坡是在更复杂的栖息地浅。我们的研究结果表明，粒径谱斜率可以作为珊瑚礁鱼类的捕捞压力的指标，但无论营养身份或功能作用的聚集鱼俯瞰捕捞压力和生境条件对食肉动物和食草动物粒径分布不同的影响。