Artificial shorelines lack natural structural complexity across scales

Abstract

From microbes to humans, habitat structural complexity plays a direct role in the provision of physical living space, and increased complexity supports higher biodiversity and ecosystem functioning across biomes. Coastal development and the construction of artificial shorelines are altering natural landscapes as humans seek socio-economic benefits and protection from coastal storms, flooding and erosion. In this study, we evaluate how much structural complexity is missing on artificial coastal structures compared to natural rocky shorelines, across a range of spatial scales from 1 mm to 10 s of m, using three remote sensing platforms (handheld camera, terrestrial laser scanner and uncrewed aerial vehicles). Natural shorelines were typically more structurally complex than artificial ones and offered greater variation between locations. However, our results varied depending on the type of artificial structure and the scale at which complexity was measured. Seawalls were deficient at all scales (approx. 20–40% less complex than natural shores), whereas rock armour was deficient at the smallest and largest scales (approx. 20–50%). Our findings reinforce concerns that hardening shorelines with artificial structures simplifies coastlines at organism-relevant scales. Furthermore, we offer much-needed insight into how structures might be modified to more closely capture the complexity of natural rocky shores that support biodiversity.

Complexity–biodiversity relationships on marine urban structures: reintroducing habitat heterogeneity through eco-engineering

“…Urban structures differ from natural habitats in the materials from which they are constructed but are also typically characterized by smooth, featureless surfaces [ 15 ]. At scales of millimetres to tens of metres, seawalls have lower structural complexity than natural rocky shores, and at the smallest and largest scales, rock revetments are similarly deficient [ 16 ].…”

Bacterial biofilm colonization and succession in tropical marine waters are similar across different types of stone materials used in seawall construction

“…One solution that is being extensively researched is to increase the topographical complexity of the seawall to provide niche availability for a wider range of species ( Loke et al, 2019 ). It is thought that anthropogenic seawall installations are lacking in complexity and thus have a reduce niche environment ( Lawrence et al, 2021 ). However, more recent investigations have highlighted that complexity alone is not universally positive with respect to increasing biodiversity, as this can be affected by local stressors, such as predation and should be seen only as an element in improving seawalls ( Chee et al, 2021 ; Strain et al, 2021 ).…”

Species diversity enhances perceptions of urban coastlines at multiple scales

“…But coastal spaces in particular, which are increasingly becoming recognised for their potential well‐being benefits (Bell et al, 2015; Bell et al, 2020; Wheeler et al, 2012), are undergoing rapid and sustained change as coastal populations continue to grow (Barragán & de Andrés, 2015; Neumann et al, 2015), and the subsequent proliferation of urban coastal structures places them in greater intersection with local communities and tourists (Evans et al, 2019). This growth of fringing coastal infrastructure and hard engineering can substantially alter the visual properties of coastal vistas at both the landscape scale and more intimate close‐up scales (Burak et al, 2004; Morgan, 1999b) through changes in shoreline structural complexity (Lawrence et al, 2021), with these simplified environments typically hosting depauperate ecological communities (Bulleri & Chapman, 2004; McKinney, 2006; Momota & Hosokawa, 2021). This has led to increasing calls to develop ecologically sensitive designs or management scenarios to retrofit coastal infrastructure, embracing varied naturalistic features to provide suitable habitat to support natural, biodiverse ecological communities (Evans et al, 2019; Firth, Schofield, et al, 2014; Firth et al, 2016).…”