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Can we enhance ecosystem-based coastal defense by connecting oysters to marsh edges? Analyzing the limits of oyster reef establishment
Ecological Engineering ( IF 3.8 ) Pub Date : 2021-04-08 , DOI: 10.1016/j.ecoleng.2021.106221
Gregory S. Fivash , Delia Stüben , Mareike Bachmann , Brenda Walles , Jim van Belzen , Karin Didderen , Ralph J.M. Temmink , Wouter Lengkeek , Tjisse van der Heide , Tjeerd J. Bouma

Nature-based coastal defense schemes commonly value bivalve reefs for i) reducing coastal erosion in the intertidal and for ii) forming fringing reefs near salt marsh edges to protect them against lateral retreat. The capacity for a reef to reduce erosion increases at a higher position in the tidal frame as the lower over-lying water level magnifies the influence of the reef on wave attenuation. Unfortunately, ecological constraints on reef development typically limit their practical application in coastal protection schemes to the lower intertidal, as bivalves grow best with long inundation times. In micro-tidal areas this is a lesser problem, given the close proximity of lower and upper intertidal ecosystems in space. By contrast, in meso- and macro-tidal estuaries, bivalve reefs tend to form hundreds of meters away from existing marshes, nullifying any wave-protective benefits. In this study, we produce evidence that with the assistance of management measures, widespread reef formation is possible on open mudflats, including bordering the marsh edge in meso- and macro-tidal estuaries, where natural reef formation is normally strongly limited.

In four locations throughout the meso- to macro-tidal Dutch Scheldt estuary, we observed the presence of individuals of two major intertidal reef-forming bivalves, Pacific oysters (Crassostrea gigas) and blue mussels (Mytilus edulis), within low-lying Spartina anglica-dominated marshes. As these communities lie well outside of the expected range of reef formation, this observation suggests the existence of mechanisms that extend the habitable range of these bivalves. In a series of field experiments, we first demonstrate how the stabilization of shell-substrate within the marsh promotes successful establishment and adult survival. Secondly, by placing artificial stable substrate in transects from the subtidal up to the marsh edge, we demonstrate that bivalve establishment is possible throughout a much larger range of the intertidal than where natural reefs occur. The effectiveness of stable substrate in stimulating bivalve establishment is likely a consequence of bridging size-dependent thresholds that limit the effective range for natural reef formation on tidal flats. The success of this approach is tempered by a consistent decrease in reef size and growth at higher elevations, suggesting that the optimal reef position for utility in coastal defense lies at an intermediate tidal position, well above the observed range of natural occurrence, but below the maximum achievable upper limit of reef formation. Together this work provides a pathway forward concerning how artificial reefs may be fostered to increase their utility as a nature-based flood defense measure.



中文翻译:

我们可以通过将牡蛎连接到沼泽边缘来增强基于生态系统的沿海防御吗?分析牡蛎礁建立的局限性

基于自然的沿海防御计划通常对i)减少潮间带的海岸侵蚀和ii)重视双壳类珊瑚礁的价值。在盐沼边缘附近形成边缘礁,以防止它们向侧面退缩。由于较低的上覆水位放大了礁石对波浪衰减的影响,礁石减少侵蚀的能力在潮汐框架中的较高位置处增加。不幸的是,由于双壳类动物在淹没时间长的情况下生长最好,因此对珊瑚礁发展的生态限制通常将其在沿海保护计划中的实际应用限制在潮间带以下。在微潮区,鉴于空间上下上下生态系统非常接近,这是一个较小的问题。相比之下,在中潮汐和大潮汐河口,双壳类生物礁往往形成于距现有沼泽数百米的地方,这使任何波浪防护作用都告一段落。在这项研究中,我们得出证据表明,借助管理措施,

在中潮至大潮汐荷兰Scheldt河口的四个位置,我们观察到低洼的Spartina anglica内有两个主要的潮间带形成礁双壳类,即太平洋牡蛎(Crassostrea gigas)和蓝贻贝(Mytilus edulis)。--占主导地位的沼泽地。由于这些群落位于珊瑚礁形成预期范围之外,因此该观察结果表明存在扩展这些双壳类动物宜居范围的机制。在一系列的野外实验中,我们首先证明了沼泽中贝壳基质的稳定化如何促进成功建立和成年生存。其次,通过将人工稳定的基质放置在从潮下带到沼泽边缘的样带中,我们证明了在整个潮间带范围内比自然礁石形成双壳类动物是可能的。稳定基质在刺激双壳类动物建立中的有效性可能是桥接大小依赖性阈值的结果,该阈值限制了潮滩上天然礁石形成的有效范围。这种方法的成功在于不断减小的礁石尺寸和在更高海拔地区的生长,这表明了在沿海防御中使用的最佳礁石位置处于中间的潮汐位置,远高于观察到的自然发生范围,但低于该范围,这是成功的关键。珊瑚礁形成的最大可达到上限。这项工作共同为如何培育人工鱼礁增加其作为基于自然的防洪措施的实用性提供了一条途径。

更新日期:2021-04-08
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