Parrotfish provide important ecological functions on coral reefs, including the provision of new settlement space through grazing and the generation of sediment through bioerosion of reef substrate. Estimating these functions at an ecosystem level depends on accurately quantifying the functional impact of individuals, yet parrotfish feeding metrics are only available for a limited range of sites, species and size classes. We quantified bite rates, proportion of bites leaving scars and scar sizes in situ for the dominant excavator (Cetoscarus ocellatus, Chlorurus strongylocephalus, Ch. sordidus) and scraper species (Scarus rubroviolaceus, S. frenatus, S. niger, S. tricolor, S. scaber, S. psittacus) in the central Indian Ocean. This includes the first record of scar frequencies and sizes for the latter three species. Bite rates varied with species and life phase and decreased with body size. The proportion of bites leaving scars and scar sizes differed among species and increased with body size. Species-level allometric relationships between body size and each of these feeding metrics were used to parameterize annual individual grazing and bioerosion rates which increase non-linearly with body size. Large individuals of C. ocellatus, Ch. strongylocephalus and S. rubroviolaceus can graze 200–400 m² and erode >500 kg of reef substrate annually. Smaller species graze 1–100 m² yr⁻¹ and erode 0.2–30 kg yr⁻¹. We used these individual functional rates to quantify community grazing and bioerosion levels at 15 sites across the Maldives and the Chagos Archipelago. Although parrotfish density was 2.6 times higher on Maldivian reefs, average grazing (3.9 ± 1.4 m² m⁻² reef yr⁻¹) and bioerosion levels (3.1 ± 1.2 kg m⁻² reef yr⁻¹) were about 15% lower than in the Chagos Archipelago (4.5 ± 2.3 and 3.7 ± 3.0, respectively), due to the dominance of small species and individuals in the Maldives (90% <30 cm length). This demonstrates that large-bodied species and individuals contribute disproportionally to both grazing and bioerosion. Across all sites, grazing increased by 66 ± 5 m² ha⁻¹ and bioerosion by 109 ± 9 kg ha⁻¹ for every kg increase in parrotfish biomass. However, for a given level of parrotfish biomass, grazing and bioerosion levels were higher on Maldivian reefs than in the Chagos Archipelago. This suggests that small-bodied fish assemblages can maintain ecosystem functions, but only if key species are present in sufficiently high numbers.

中文翻译：

---

鹦嘴鱼放牧和生物侵蚀的位点水平变化与特定物种的饲养指标有关

鹦嘴鱼在珊瑚礁上具有重要的生态功能，包括通过放牧提供新的定居空间以及通过对珊瑚礁底物的生物侵蚀产生沉积物。在生态系统水平上估计这些功能取决于准确量化个体的功能影响，但是鹦鹉鱼的摄食指标仅适用于有限范围的地点，物种和大小类别。我们定量分析了优势挖掘机（Cetoscarus ocellatus，Chlorurus strongylocephalus，Ch。sordidus）和刮板种类（Scarus rubroviolaceus，S.frenatus，S.niger，S.nicolor，S。 scaber，S. psittacus）在印度洋中部。这包括后三个物种的疤痕频率和大小的第一笔记录。叮咬率随物种和生命阶段而变化，随体型而降低。不同物种之间留下疤痕的咬伤比例和疤痕大小不同，并且随体型增加。体重与这些摄食指标中的每一个之间的物种水平异位关系被用来参数化个体放牧和生物侵蚀率，它们随体型呈非线性增加。大个体的C. ocellatus，Ch。strongylocephalus和S. rubroviolaceus可以轻擦200-400米²每年和侵蚀>500公斤礁衬底。较小的物种以1–100 m ² yr ^-1放牧，以0.2–30 kg yr的侵蚀^-1。我们使用这些单独的功能比率来量化马尔代夫和查戈斯群岛15个地点的社区放牧和生物侵蚀水平。尽管在马尔代夫珊瑚礁上鹦嘴鱼的密度高出2.6倍，但平均放牧（3.9±1.4 m ² m ^-2礁yr ^-1）和生物侵蚀水平（3.1±1.2 kg m ^-2礁yr ^-1）较印度洋低约15％。查戈斯群岛（分别为4.5±2.3和3.7±3.0），原因是小物种和个体在马尔代夫占主导地位（90％<30 cm长）。这表明，大物种和个体对放牧和生物侵蚀的贡献不成比例。在所有地点，放牧增加了66±5 m ²鹦鹉鱼生物量每增加¹ kg，ha ^-1和生物侵蚀就增加109±9 kg ha ^-1。但是，对于给定的鹦嘴鱼生物量水平，马尔代夫礁的放牧和生物侵蚀水平高于查戈斯群岛。这表明，只有在关键物种数量足够多的情况下，小鱼体才能维持生态系统功能。