Seagrass coastal protection services reduced by invasive species expansion and megaherbivore grazing
Seagrass coastal protection services reduced by invasive species expansion and megaherbivore grazing
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DOI：
10.1111/1365-2745.13411
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发表时间：
2020-05-31
影响因子：
5.5
通讯作者：
Bouma, Tjeerd J.
中科院分区：
文献类型：
--
作者：
James, Rebecca K.;Christianen, Marjolijn J. A.;Bouma, Tjeerd J.
海草提供了重要的生态系统服务，因为它形成了稳定的抗侵蚀海床，有助于有效保护海岸。然而，不同的形态和生活史策略可能会影响不同海草物种的沉积物稳定能力。我们质疑机会主义入侵物种和大型食草动物放牧的增加可能会改变沉积物稳定服务所提供的既定海草草甸，使用加勒比海作为一个案例study.Utilizing两个便携式现场水槽，模拟单向和振荡流制度，我们比较了沉积物稳定能力的天然海草草甸在原地电流和波浪为主的制度。比较了一种本地海草（Thalassia testudinum）和一种入侵海草（Halophila stipulacea）的单种斑块，沿着了三种水平的大型草食动物放牧对T.在这两种水动力条件下，顶极种龟鳖T. testudinum提供了最高的稳定性。然而，密集放牧造成的地上生物量损失降低了本地海草稳定表层沉积物的能力。加勒比海的海草草甸目前正受到入侵的机会性海草H.托叶类H.发现托叶可以积累细沉积物，因此，在平静期间，似乎可以有效地减少底部剪切应力。然而，在入侵草甸内的这些细沉积物很容易被水动力重新悬浮，并且H.托叶使其在风暴期间容易被连根拔起，可能使大片地区容易受到侵蚀。总体而言，本研究强调，密集的大型草食动物放牧和机会主义入侵物种威胁到轻度放牧的本地物种提供的海岸保护服务。密集的长叶海草草甸稳定了沉积物表面，保持了海底的完整性，从而有助于海岸保护。这些服务受到以下因素的威胁：大型食草动物的密集放牧，降低了表层沉积物的稳定性;机会性入侵物种，在风暴中很容易连根拔起，从而使海底容易受到侵蚀。
Seagrasses provide an important ecosystem service by creating a stable erosion-resistant seabed that contributes to effective coastal protection. Variable morphologies and life-history strategies, however, are likely to impact the sediment stabilization capacity of different seagrass species. We question how opportunistic invasive species and increasing grazing by megaherbivores may alter sediment stabilization services provided by established seagrass meadows, using the Caribbean as a case study.Utilizing two portable field-flumes that simulate unidirectional and oscillatory flow regimes, we compared the sediment stabilization capacity of natural seagrass meadows in situ under current- and wave-dominated regimes. Monospecific patches of a native (Thalassia testudinum) and an invasive (Halophila stipulacea) seagrass species were compared, along with the effect of three levels of megaherbivore grazing on T. testudinum: ungrazed, lightly grazed and intensively grazed.For both hydrodynamic regimes, the long-leaved, dense meadows of the climax species, T. testudinum provided the highest stabilization. However, the loss of above-ground biomass by intensive grazing reduced the capacity of the native seagrass to stabilize the surface sediment. Caribbean seagrass meadows are presently threatened by the rapid spread of the invasive opportunistic seagrass, H. stipulacea. The dense meadows of H. stipulacea were found to accumulate fine sediment, and thereby, appear to be effective in reducing bottom shear stress during calm periods. This fine sediment within the invasive meadows, however, is easily resuspended by hydrodynamic forces, and the low below-ground biomass of H. stipulacea make it susceptible to uprooting during storm events, potentially leaving large regions vulnerable to erosion. Overall, this present study highlights that intensive megaherbivore grazing and opportunistic invasive species threaten the coastal protection services provided by mildly grazed native species.Synthesis. Seagrass meadows of dense, long-leaved species stabilize the sediment surface and maintain the seabed integrity, thereby contributing to coastal protection. These services are threatened by intensive megaherbivore grazing, which reduces the stability of the surface sediment, and opportunistic invasive species, which are susceptible to uprooting in storms and thereby can leave the seabed vulnerable to erosion.