Food partitioning among coexisting species is often considered advantageous to minimize niche overlap and avoid inter-specific competition. Congeneric fish species such as the mullets Mugil curema and Mugil liza, which co-occur across marine and estuarine habitats, are good models to evaluate resource use and niche overlap or partitioning. We used stomach contents (SCA) and stable isotope analysis (SIA) to assess potential trophic shifts and changes in niche overlap associated with the mullets transitioning from marine to estuarine habitats. SIA included different fractions of organic matter in suspension and in the sediment to estimate the contribution of micro, nano and pico-organisms to the mullets’ diets. We hypothesized higher resource partitioning in the less resource-diverse system (marine surf-zone) than in the more diverse one (estuary). SCA showed diet differences between M. curema and M. liza according to the habitat. They showed distinct diets in the marine area (P < 0.001), but similar diets in the estuary (P = 0.226). A lower niche breadth was observed for both species in the marine area (M. curema = 0.03, M. liza = 0.06) compared with the estuary (M. curema = 0.14, M. liza = 0.16). Isotopic niches of both species were higher in the estuary (64.7%) compared with the marine area (0.7%). These findings corroborated our hypothesis of higher food partitioning in the marine surf-zone. We also demonstrated using SIA the shift from planktonic to benthic feeding following the recruitment of the mullets from the surf-zone into the estuary.

中文翻译：

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海洋和河口生境共存的鲻鱼幼鱼的营养生态位和饮食变化

共存物种之间的食物分配通常被认为有利于最大限度地减少生态位重叠并避免种间竞争。鲻鱼等同类鱼类鹧鸪和穆吉尔丽莎，在海洋和河口栖息地共同发生，是评估资源利用和生态位重叠或分区的好模型。我们使用胃内容物 (SCA) 和稳定同位素分析 (SIA) 来评估与鲻鱼从海洋栖息地过渡到河口栖息地相关的潜在营养变化和生态位重叠变化。SIA 包括了悬浮液和沉积物中不同部分的有机物，以估计微米、纳米和微型生物对鲻鱼饮食的贡献。我们假设在资源多样性较低的系统（海洋冲浪区）中的资源划分比在更多样化的系统（河口）中更高。SCA显示饮食差异M.curema和丽莎根据栖息地。他们在海洋区域表现出不同的饮食（磷< 0.001)，但河口的饮食相似 (磷= 0.226)。在海洋区域观察到两个物种的生态位宽度较低（M.curema= 0.03,丽莎= 0.06) 与河口 (M.curema= 0.14,丽莎= 0.16)。两个物种的同位素生态位在河口（64.7%）高于海洋区域（0.7%）。这些发现证实了我们关于海洋冲浪区食物分配较高的假设。我们还使用 SIA 演示了在将鲻鱼从冲浪区招募到河口后从浮游生物向底栖生物喂养的转变。