Voerman Sofie E, Glasby Tim M, Gladstone William, Gribben Paul E
School of Life Sciences, University of Technology Sydney, NSW 2007, Australia; Climate Change Cluster, University of Technology Sydney, NSW 2007, Australia(1).
New South Wales Department of Primary Industries, Port Stephens Fisheries Institute, Locked Bag 1, Nelson Bay, NSW 2315, Australia.
Mar Environ Res. 2017 Oct;131:205-214. doi: 10.1016/j.marenvres.2017.09.019. Epub 2017 Sep 28.
There are many examples of native macrophytes becoming locally dominant and spreading outside their traditional distributions, but the causes and impacts are often not understood. In New South Wales, Australia, the green alga Caulerpa filiformis is undergoing a range expansion and has transitioned from a subdominant to a dominant alga on several rocky shores around the Sydney coastline. Here we investigated relationships between established patches of C. filiformis, the habitat it occupies and associated algal communities at multiple subtidal sites over the green alga's 700 km range. We tested the following predictions: 1) C. filiformis cover differs among substrata, being greatest on turf-forming algae; 2) C. filiformis cover is positively related to environmental variables linked to increased sedimentation (e.g. reduced reef width, surface slope, increased rugosity and distance from shore); 3) occurrence of C. filiformis is associated with a change in macrophyte community structure and a reduction of macrophyte richness; 4) intact native algal canopies inhibit C. filiformis spread, but turf-forming algae and bare sand are susceptible to invasion. Substratum associations were highly consistent among sites, but contrary to our prediction, C. filiformis was most commonly associated with rock or rock + sand substratum and less frequently associated with turf-forming algae substratum. C. filiformis cover was negatively correlated with reef width, which explained most of the variation observed, although local scale variables distance from shore, reef slope, and water depth were also correlated with C. filiformis cover. Algal diversity and community composition typically differed in the presence of C. filiformis, often with a reduction of algal abundances, in particular Sargassum spp., although results varied among substrata and sites. However, monitoring of borders suggested that C. filiformis does not invade and outcompete undisturbed adjacent canopy-forming algae over a 12 month period. Our results suggest that disturbance processes (possibly linked to sedimentation) acting at the site and quadrat scale are likely important determinants of C. filiformis cover and spread, and hence its potential ecological impacts.
本地大型植物在当地占据主导地位并扩散至其传统分布范围之外的例子有很多，但人们往往并不了解其成因和影响。在澳大利亚新南威尔士州，丝状蕨藻正在扩大其分布范围，并且在悉尼海岸线周围的多个岩石海岸已从亚优势藻类转变为主导藻类。在此，我们调查了在丝状蕨藻700公里的分布范围内，多个潮下带地点已形成的丝状蕨藻斑块、其占据的栖息地以及相关藻类群落之间的关系。我们检验了以下预测：1）丝状蕨藻的覆盖度在不同基质间存在差异，在形成草皮的藻类上最大；2）丝状蕨藻的覆盖度与与沉积增加相关的环境变量呈正相关（例如，礁体宽度减小、表面坡度、粗糙度增加以及离岸距离增加）；3）丝状蕨藻的出现与大型植物群落结构的变化以及大型植物丰富度的降低有关；4）完整的本地藻冠会抑制丝状蕨藻的扩散，但形成草皮的藻类和裸沙易受入侵。各地点之间基质关联高度一致，但与我们的预测相反，丝状蕨藻最常与岩石或岩石 + 沙子基质相关，而与形成草皮的藻类基质的关联较少。丝状蕨藻的覆盖度与礁体宽度呈负相关，这解释了观察到的大部分变化，尽管局部尺度变量离岸距离、礁体坡度和水深也与丝状蕨藻的覆盖度相关。在有丝状蕨藻存在的情况下，藻类多样性和群落组成通常会有所不同，藻类丰度往往会降低，特别是马尾藻属，尽管结果因基质和地点而异。然而，对边界的监测表明，在12个月的时间里，丝状蕨藻不会入侵并胜过未受干扰的相邻冠层形成藻类。我们的结果表明，在地点和样方尺度上起作用的干扰过程（可能与沉积有关）可能是丝状蕨藻覆盖度和扩散的重要决定因素，因此也是其潜在生态影响的重要决定因素。
