The Effects of Substrate Texture, Grazing, and Disturbance on Macroalgal Establishment in Streams
The Effects of Substrate Texture, Grazing, and Disturbance on Macroalgal Establishment in Streams
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基质质地、放牧和干扰对溪流中巨藻生长的影响
DOI：
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发表时间：
1991
期刊：
影响因子：
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通讯作者：
C. D’Antonio
中科院分区：
文献类型：
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作者：
T. Dudley;C. D’Antonio
两种常见的大型藻类，Cladophora glomerata（一种丝状叶绿藻）和Nostoc parmeloides（一种群落蓝藻），与响尾蛇溪（加利福尼亚州圣巴巴拉县沿海的二级河流）的粗糙基质密切相关。为了检验粗糙质地降低无脊椎动物食草动物和冬季风暴造成的藻类死亡率的假设，我们对两种仅表面异质性不同的基质类型（标题）进行了一系列实验。使用凡士林屏障将主要食草动物石蛾 Agapetus celatus 排除在瓷砖之外，并将藻类的形成与对照瓷砖上的进行比较；春季和秋季重复放牧实验。在一项单独的实验中，从 12 月到 6 月，通过以不同的时间间隔（7 周、3 周和一次，不受干扰的对照）手动擦洗自然定殖的粗糙和光滑瓷砖来模拟风暴冲刷，在此期间监测藻类的繁殖和存活。在没有 Agapetus 的情况下，在粗糙和光滑的表面上几乎同样发现了刚毛虫。食草动物极大地减少了刚毛虫在所有表面上的繁殖（通常减少了 80% 以上）；质地通常不会影响秋季的放牧效果，但避难所（坑）在春季补充量较多时大大增加了藻类的存活率。其他两种食草昆虫（Baetis spp. 和 Micrasema）在排除瓷砖上有所增加，显然是由于竞争性释放，但并没有消除 Agapetus 的影响。每隔 3 周和 7 周进行的人工干扰使刚毛虫密度远低于对照和一次擦洗的瓷砖。粗糙瓷砖上的密度较高，但对于大型藻类来说，干扰和纹理之间的相互作用并不显着；然而，显微镜检查表明基底丝和新的孢子体在凹陷处受到保护。秋季，发菜在粗糙瓷砖上的密度达到 50—100 个菌落/100 cm2，而在光滑瓷砖上几乎不存在。与刚毛藻不同，发菜受放牧影响很小，但受干扰却大大减少。粗糙的质地提供了轻微的保护，但成熟的发菜形成了抵抗干扰的基底壳，从而在没有严重冲刷的情况下保持了空间。基质异质性为大型藻类的建立提供了免受食草和干扰的庇护所。虽然食草动物在决定溪流中的藻类动态方面发挥着深远的作用，但食草动物和基质纹理也可能相互作用，从而改变底栖演替的速度和方向。通过抑制中间类群（例如刚毛藻）的建立，食草动物可能会将光滑基质上的演替限制为早期以硅藻为主的组合，或加速后期类群（例如发菜）在粗糙基质上的优势。
Two common macroalgae, Cladophora glomerata (a filamentous chlorophyte) and Nostoc parmeloides (a colonial cyanobacterium), are strongly associated with rough substrates in Rattlesnake Creek, a second—order stream in coastal Santa Barbara County, California. To test the hypothesis that rough texture reduces algal mortality from invertebrate grazers and from winter storms, we conducted a series of experiments on two substrate types (titles) that varied only in surface heterogeneity. The dominant grazer, the caddisfly Agapetus celatus, was excluded from tiles using petroleum jelly barriers, and algal establishment was compared with that on control tiles; grazing experments were repeated during spring and autumn. In a separate experiment, storm scouring was simulated by manually scrubbing naturally colonized rough and smooth tiles at different intervals (7 wk, 3 wk, and once, with an undisturbed control) from December to June, during which algal establishment and survival were monitored. In the absence of Agapetus, Cladophora was found nearly equally on rough and smooth surfaces. Grazers strongly reduced Cladophora establishment on all surfaces (often by >80%); texture did not generally influence grazing effects in autumn, but refuges (pits) greatly increased algal survival in spring when recruitment was greater. Two other grazing insects (Baetis spp. and Micrasema) increased on exclusion tiles, apparently due to competitive release, but did not eliminate effects of Agapetus. Manual disturbance at 3— and 7—wk intervals kept Cladophora densities much lower than on control and once—scoured tiles. Densities were higher on rough tiles, but the interaction between disturbance and texture was not significant for macroalgae; however, microscopic examination showed that basal filaments, and new sporelings, were protected within depressions. Nostoc attained densities in autumn of °50—100 colonies/100 cm2 on rough tiles and was virtually absent from smooth tiles. Unlike Cladophora, Nostoc was little affected by grazing, but was greatly reduced by disturbance. Rough texture provided minor protection, but mature Nostoc formed basal crusts that resisted disturbance, thereby maintaining space in the absence of severe scour. Substrate heterogeneity provides refuges from herbivory and disturbance for establishing macroalgae. While it increasingly appears that herbivory plays a profound role in determining algal dynamics in streams, herbivores and substrate texture may also interact to modify the rate and direction of benthic succession. By inhibiting the establishment of intermediate taxa (e.g., Cladophora), grazers may restrict succession on smooth substrates to an early, diatom—dominated assemblage, or accelerate dominance by later taxa (e.g., Nostoc) on rugose substrates.