Anthropogenic Disturbance Can Determine the Magnitude of Opportunistic Species Responses on Marine Urban Infrastructures

BackgroundCoastal landscapes are being transformed as a consequence of the increasing demand for infrastructures to sustain residential, commercial and tourist activities. Thus, intertidal and shallow marine habitats are largely being replaced by a variety of artificial substrata (e.g. breakwaters, seawalls, jetties). Understanding the ecological functioning of these artificial habitats is key to planning their design and management, in order to minimise their impacts and to improve their potential to contribute to marine biodiversity and ecosystem functioning. Nonetheless, little effort has been made to assess the role of human disturbances in shaping the structure of assemblages on marine artificial infrastructures. We tested the hypothesis that some negative impacts associated with the expansion of opportunistic and invasive species on urban infrastructures can be related to the severe human disturbances that are typical of these environments, such as those from maintenance and renovation works.
Methodology/Principal FindingsMaintenance caused a marked decrease in the cover of dominant space occupiers, such as mussels and oysters, and a significant enhancement of opportunistic and invasive forms, such as biofilm and macroalgae. These effects were particularly pronounced on sheltered substrata compared to exposed substrata. Experimental application of the disturbance in winter reduced the magnitude of the impacts compared to application in spring or summer. We use these results to identify possible management strategies to inform the improvement of the ecological value of artificial marine infrastructures.
Conclusions/SignificanceWe demonstrate that some of the impacts of globally expanding marine urban infrastructures, such as those related to the spread of opportunistic, and invasive species could be mitigated through ecologically-driven planning and management of long-term maintenance of these structures. Impact mitigation is a possible outcome of policies that consider the ecological features of built infrastructures and the fundamental value of controlling biodiversity in marine urban systems.

背景
随着支撑居住、商业及旅游活动的基础设施需求持续增长，沿海景观正发生深刻变革。为此，潮间带与浅海生境正大量被各类人工基质（artificial substrata，如防波堤、海堤、突堤码头）所替代。明确这类人工生境的生态功能，是规划其设计与管理的核心所在，可最大限度降低其负面影响，并提升其助力海洋生物多样性与生态系统功能的潜力。尽管如此，目前针对人类扰动如何塑造海洋人工基础设施上生物群落结构的研究仍较为匮乏。本研究验证了一项假说：城市人工基础设施上机会主义物种与入侵物种扩张所带来的部分负面影响，或与这类环境典型的强烈人类扰动（如维护与翻新工程）相关。

方法与主要发现
维护工程会显著降低贻贝、牡蛎等优势空间占有物种的盖度，并大幅促进生物膜（biofilm）、大型藻类（macroalgae）等机会主义与入侵类群的生长。相较于受侵蚀基底，这类效应在庇护型基底上表现得更为显著。实验表明，相较于春季或夏季施加扰动，冬季实施扰动可降低此类影响的强度。本研究基于上述结果，提出了可用于提升海洋人工基础设施生态价值的潜在管理策略。

结论与意义
本研究证实，全球范围内不断扩张的海洋城市基础设施所带来的部分负面影响（如与机会主义及入侵物种扩散相关的影响），可通过以生态为导向的规划与长期维护管理工作加以缓解。若相关政策能够兼顾人工基础设施的生态特性，以及管控海洋城市系统生物多样性的核心价值，那么减轻生态影响便可成为政策实施的可行成果之一。