Data from: The role of fish feces for nutrient cycling on coral reefs

Consumers play an important role in biogeochemical cycles through the consumption and release of essential elements such as carbon (C), nitrogen (N), and phosphorus (P). Indeed, a large proportion of consumed elements are released into the environment in inorganic (i.e., excretion) or organic form (i.e., egestion). On coral reefs, fishes represent the bulk of consumer biomass and thus play a key role in the recycling of nutrients. In recent years, excretion rates have been studied intensively, but less is known about the rate and quality of coral reef fish egestion. In this study, we quantify the elemental contents of fish feces, estimate absorption efficiencies and compare egestion and excretion rates for 51 coral reef fish species. We show that elemental concentrations decrease remarkably little from food to feces. This is due to extremely low absorption efficiencies, resulting in the egestion of large amounts of energy and nutrients. Moreover, we show that while the quality of fish feces varies across trophic guilds, it remains highly variable within trophic guilds. Finally, we demonstrate that the release of N and P through egestion outweighs the amount of nutrients recycled through excretion. Our study highlights the need to incorporate animal egestion into assessments of ecosystem functioning and food web structure.

消费者通过摄取并释放碳（C）、氮（N）、磷（P）等必需元素，在生物地球化学循环中发挥重要作用。事实上，被摄取的元素中有很大一部分会以无机形式（即排泄(excretion)）或有机形式（即排遗(egestion)）释放到环境中。在珊瑚礁生态系统中，鱼类构成了消费者生物量的主体，因此在营养物质循环中发挥关键作用。近年来，学界针对鱼类排泄速率开展了大量深入研究，但对珊瑚礁鱼类排遗的速率与质量的了解仍较为有限。本研究中，我们对51种珊瑚礁鱼类的粪便元素含量进行了定量分析，估算了其营养吸收效率，并对比了排遗与排泄速率。研究发现，从食物到粪便，元素浓度的降幅极小。这是因为鱼类的营养吸收效率极低，导致大量能量与营养物质通过排遗被释放。此外，研究还发现，鱼类粪便的质量会随营养类群(trophic guilds)的不同而产生差异，但同一营养类群内部的粪便质量仍存在极高的变异性。最后，本研究证实，通过排遗释放的氮与磷量，超过了通过排泄循环的营养物质总量。本研究强调，在生态系统功能与食物网结构的评估中，有必要纳入动物排遗这一环节。