Effects of experimentally added salmon subsidies on resident fishes via direct and indirect pathways
Effects of experimentally added salmon subsidies on resident fishes via direct and indirect pathways
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实验性添加鲑鱼补贴通过直接和间接途径对居民鱼类的影响
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发表时间：
2016
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影响因子：
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通讯作者：
M. Wipfli
中科院分区：
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作者：
S. Collins;C. Baxter;Amy M. Marcarelli;M. Wipfli
人工添加不同形式的营养物质，如鲑鱼尸体和类似颗粒（即巴氏灭菌鱼粉），已被提议作为刺激水产生产力和增加溯河产卵和留栖鱼类数量的一种手段。为了提高河流生态系统中的鱼类产量而进行的营养物减缓假设，影响发生的中心途径是自下而上的，通过水生初级和次级生产，很少考虑水生-陆地的相互途径。将鲑鱼衍生材料添加到溪流中的最终结果（即自下而上与自上而下）取决于这些补贴是否通过增加共同捕食者间接加剧对原地猎物的捕食或减轻这种捕食压力。我们在美国爱达荷州博伊西北福克河的九个支流上进行了一项为期 3 年的实验，其中包括用鲑鱼尸体处理的 500 米河段 (n = 3)、鲑鱼尸体模拟物 (n = 3) 和未经处理的对照河段 (n = 3)。我们观察到，在第 1 年和第 2 年添加鲑鱼补贴处理后的 2-6 周内，河床生物膜增加了 2-8 倍，而在实验的第二年，水生无脊椎动物的活体作物生物量与尸体添加量增加了 1.5 倍。在同一时间范围内，溪流鱼类对底栖无脊椎动物的消耗量增加了 110–140%，尸体和类似溪流中的 44–66%，这可能掩盖了第 3 年和第 4 年无脊椎动物的常备作物反应。居民鳟鱼直接消耗了 10.0–24.0 g·m−2·yr−1 的鲑鱼尸体和 <1–11.0 g·m−2·yr−1 的类似物材料，产生 1.2–2.9 g·m−2·yr−1 和 0.03–1.4 g·m−2·yr−1 的组织。此外，陆生蛆对溪流的反馈通量对鳟鱼产量贡献了 0.0–2.0 g·m−2·yr−1。总体而言，处理使鳟鱼的年产量增加了 2-3 倍，但密度和生物量不受影响。我们的研究结果表明，自下而上和自上而下对补贴增加的反应强度是不对称的，自上而下的力量掩盖了需要多年才能显现的自下而上的影响。研究结果还强调，营养物减缓计划需要考虑能量和营养物流动的多种途径，以解释鲑鱼补贴对溪流河岸生态系统的复杂影响。
Artificial additions of nutrients of differing forms such as salmon carcasses and analog pellets (i.e. pasteurized fishmeal) have been proposed as a means of stimulating aquatic productivity and enhancing populations of anadromous and resident fishes. Nutrient mitigation to enhance fish production in stream ecosystems assumes that the central pathway by which effects occur is bottom-up, through aquatic primary and secondary production, with little consideration of reciprocal aquatic-terrestrial pathways. The net outcome (i.e. bottom-up vs. top-down) of adding salmon-derived materials to streams depend on whether or not these subsidies indirectly intensify predation on in situ prey via increases in a shared predator or alleviate such predation pressure. We conducted a 3-year experiment across nine tributaries of the N. Fork Boise River, Idaho, USA, consisting of 500-m stream reaches treated with salmon carcasses (n = 3), salmon carcass analog (n = 3), and untreated control reaches (n = 3). We observed 2–8 fold increases in streambed biofilms in the 2–6 weeks following additions of both salmon subsidy treatments in years 1 and 2 and a 1.5-fold increase in standing crop biomass of aquatic invertebrates to carcass additions in the second year of our experiment. The consumption of benthic invertebrates by stream fishes increased 110–140% and 44–66% in carcass and analog streams in the same time frame, which may have masked invertebrate standing crop responses in years 3 and 4. Resident trout directly consumed 10.0–24.0 g·m−2·yr−1 of salmon carcass and <1–11.0 g·m−2·yr−1 of analog material, which resulted in 1.2–2.9 g·m−2·yr−1 and 0.03–1.4 g·m−2·yr−1 of tissue produced. In addition, a feedback flux of terrestrial maggots to streams contributed 0.0–2.0 g·m−2·yr−1 to trout production. Overall, treatments increased annual trout production by 2–3 fold, though density and biomass were unaffected. Our results indicate the strength of bottom-up and top-down responses to subsidy additions was asymmetrical, with top-down forces masking bottom-up effects that required multiple years to manifest. The findings also highlight the need for nutrient mitigation programs to consider multiple pathways of energy and nutrient flow to account for the complex effects of salmon subsidies in stream-riparian ecosystems.