The productivity of most marine ecosystems is limited by the availability of dissolved nitrogen (N) and phosphorus (P). Nutrient recycling is therefore a key process for ecosystem functioning. Fish recycle nutrients through the excretion of ammonia and phosphate and can influence the abundance and community structure of primary producers such as phytoplankton. However, the effect of fish on other plankton compartments, and whether all fish species have similar effects, is largely unknown. We used a tank experiment to test how 2 Mediterranean fish species, gilthead seabream Sparus aurata and golden mullet Chelon auratus, with distinctly different N and P excretion rates, can affect the abundance and community structure of 3 plankton compartments: phytoplankton, bacterioplankton, and microzooplankton. We found that the nutrients released by seabream (whose excreta had an N:P molar ratio greater than the Redfield ratio of 16:1) induced a substantial increase in the abundance of all plankton compartments. In addition, with seabream, the relative abundance of diatoms in the phytoplankton communities increased. However, no significant change was observed with mullet, which had a low excreta N:P molar ratio, suggesting that the growth of microbial plankton was limited by the availability of N. Our results demonstrate that nutrient excretion by fish affects the microbial food web through a species-specific bottom-up effect on the total abundance and community structure of the phytoplankton, bacterioplankton, and microzooplankton communities.

中文翻译：

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鱼类对海洋微生物浮游生物影响的种间差异

大多数海洋生态系统的生产力受到溶解氮 (N) 和磷 (P) 的可用性的限制。因此，养分循环是生态系统功能的关键过程。鱼类通过排泄氨和磷酸盐来循环养分，并可影响浮游植物等初级生产者的丰度和群落结构。然而，鱼类对其他浮游生物区室的影响，以及是否所有鱼类都有类似的影响，在很大程度上是未知的。我们使用水族箱实验来测试 2 种地中海鱼类，即金头鲷 Sparus aurata 和金鲻鱼 Chelon auratus，它们的 N 和 P 排泄率明显不同，如何影响浮游植物、浮游细菌和微型浮游动物 3 种浮游生物区室的丰度和群落结构. 我们发现鲷鱼（其排泄物的 N:P 摩尔比大于 16:1 的 Redfield 比率）释放的营养物质导致所有浮游生物区室的丰度显着增加。此外，对于鲷鱼，浮游植物群落中硅藻的相对丰度增加。然而，鲻鱼的排泄物 N:P 摩尔比较低，没有观察到显着变化，这表明微生物浮游生物的生长受到 N 的可用性的限制。我们的结果表明，鱼类的营养排泄通过以下方式影响微生物食物网对浮游植物、浮游细菌和微型浮游动物群落的总丰度和群落结构的物种特异性自下而上的影响。1) 导致所有浮游生物区室的丰度大幅增加。此外，对于鲷鱼，浮游植物群落中硅藻的相对丰度增加。然而，鲻鱼的排泄物 N:P 摩尔比较低，没有观察到显着变化，这表明微生物浮游生物的生长受到 N 的可用性的限制。我们的结果表明，鱼类的营养排泄通过以下方式影响微生物食物网对浮游植物、浮游细菌和微型浮游动物群落的总丰度和群落结构的物种特异性自下而上的影响。1) 导致所有浮游生物区室的丰度大幅增加。此外，对于鲷鱼，浮游植物群落中硅藻的相对丰度增加。然而，鲻鱼的排泄物 N:P 摩尔比较低，没有观察到显着变化，这表明微生物浮游生物的生长受到 N 的可用性的限制。我们的结果表明，鱼类的营养排泄通过以下方式影响微生物食物网对浮游植物、浮游细菌和微型浮游动物群落的总丰度和群落结构的物种特异性自下而上的影响。