1. Tropical short, steep coastal streams are typically dominated by diadromous species, especially amphidromous fishes, crustaceans, and molluscs. We undertook a study to determine the distribution of fishes along the stream continuum and determine if substantial natural instream barriers influenced assemblage composition.
2. We surveyed fish assemblages in three short, steep coastal streams in the Australian Wet Tropics by snorkelling and performing single pass counts in each 100‐m section along the entire main channel from the high‐tide mark to the source (or near source: until fish were no longer recorded). A primary focus was mapping the distribution and relative abundance of sicydiine gobies, and we also estimated freshwater crustacean numbers (Caridea: Palaemonidae and Atyidae).
3. In total, 2,837 individual fish of 25 species were recorded upstream of the high‐tide mark across the three streams and the first records of an additional sicydiine goby (Smilosicyopus leprurus) were obtained from continental Australia. Consistent with findings from tropical Pacific island streams, we observed a shift in fish assemblage composition along the elevation gradient and in relation to major instream barriers (e.g. waterfalls >5 m, and high flow chutes across smooth bedrock surfaces). Species richness of diurnal predatory fishes was greatest in the lower course of streams and absent upstream of major instream barriers.
4. Diurnal predatory fishes were, in some instances, found upstream of barriers. Specifically, large adult (>200 mm total length) Kuhlia rupestris (diurnal predators) accessed reaches above challenging sequences of cascades combined with small waterfalls. In contrast, all sizes of that species, adult Kuhlia marginata (>150 mm total length) and a diversity of other diurnal predatory fishes occupied the lower course of streams including upstream of gentle cascade sequences or isolated small waterfalls.
5. Where abundances of diurnal predatory fishes were high, freshwater carideans were rarely observed. Peak densities of carideans were observed upstream of major barriers, with moderate densities in the upper mid‐course in the presence of few Kuhlia spp.
6. The current study demonstrates the value of complete single‐pass surveys of fish assemblages in tropical short, steep coastal streams by revealing the highly localised occupation of particular reaches by rare fishes. It also points towards the importance of stream‐specific characteristics, namely the position of waterfalls in dictating diadromous predator distribution with consequences for community structure, thereby aligning with the Riverine Discontinuum Concept.

中文翻译：

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瀑布介导在热带，短而陡峭的沿海溪流中构成水族的掠食性鱼类的纵向分布

1. 热带短而陡峭的沿海溪流通常以二足类鱼类为主，尤其是两栖鱼类，甲壳类和软体动物。我们进行了一项研究，以确定沿河连续体的鱼类分布，并确定是否有实质性的自然河内障碍物影响了鱼类的组成。
2. 我们通过浮潜并在从高潮标记到源头（或附近源头：直到鱼类）的整个主要通道的每个100米区域中进行浮潜和单次通过计数，对澳大利亚湿热带地区三条短而陡峭的沿海溪流中的鱼类群落进行了调查。不再记录）。主要重点是绘制西西丁虾虎鱼的分布和相对丰度，我们还估算了淡水甲壳类动物的数量（Caridea：Palaemonidae和Atyidae）。
3. 总共在三条溪流的高潮标记上游记录了2,837条25种鱼类，并且从澳大利亚大陆获得了另外的西西丁虾虎鱼（Smilosicyopus leprurus）的第一条记录。与热带太平洋岛屿溪流的发现一致，我们观察到鱼群组成沿海拔梯度的变化以及与主要河道屏障（例如，瀑布> 5 m，以及穿过光滑基岩表面的高流量滑槽）有关。昼间掠食性鱼类的物种丰富度在河道的下游最大，而在主要河道屏障的上游却没有。
4. 在某些情况下，昼夜掠食性鱼类是在障碍物上游发现的。具体而言，进入的大型成年动物（总长度大于200毫米）天竺葵（昼间捕食者）达到了具有挑战性的小瀑布与小瀑布相结合的序列。相反，该物种的所有大小，成年的Kuhlia marginata（总长度> 150 mm）和其他各种昼夜掠食性鱼类都占据了下游水流，包括上游的缓和级联序列或孤立的小瀑布。
5. 在昼夜掠食性鱼类丰富的地方，很少观察到淡水Carideans。在主要障碍的上游观察到了最高峰密度，在中部只有少数Kuhlia物种的情况下，其中层密度中等。
6. 当前的研究通过揭示稀有鱼类对特定河段的高度局部化占领，证明了对热带短而陡峭的沿海河流鱼群进行完整的单次调查的价值。它还指出了特定于河流的特征的重要性，即瀑布在指示过分捕食者分布并影响社区结构方面的位置，从而与Riverine Discontinuum概念保持一致。