How and to What Degree Does Physical Structure Differ Between Natural and Artificial Habitats? A Multi-Scale Assessment in Marine Intertidal Systems

Abstract

Marine infrastructures are increasing, generating a variety of impacts and introducing artificial habitats which have low ecological value and support assemblages that differ significantly from those on natural rocky coasts. While in the past there was little ecological consideration as to how artificial structures were built, now the trend is to look for “greener” designs inspired by or mimicking nature. These greening efforts have had a strong focus on enhancing physical habitat structure to support more diverse assemblages, driven by the untested assumption that artificial habitats lack the physical structure proper to natural habitats. We tested this assumption by comparing five descriptors of physical structure (inclination; exposure; roughness; abundance, and diversity of surface morphological microelements) across a combination of natural and artificial habitats of regular and irregular morphologies (seawalls = artificial regular; cliffs = natural regular; breakwaters = artificial, irregular; and boulder fields = natural irregular) in the North Adriatic Sea. Most structural descriptors were similar between artificial and natural habitats. Only inclination was consistently steeper in the artificial than in the natural habitats. Other minor differences in roughness or in the abundance of some surface microelements were related to the general morphology (regular or irregular) of the habitat rather than to its artificial or natural identity. The outcomes challenge the widespread assumption that artificial habitats lack the physical structure proper to natural habitats and stimulate renewed consideration about other structural and non-structural elements that could enhance the performance and sustainability of artificial marine structures, such as construction material, environmental setting or maintenance. They also encourage a wider reflection about what makes an artificial building surface “greener”: structural complexity is an important ecological parameter, and its deliberate increase will lead to responses in the biota, however, this may not necessarily match “more natural” conditions.

Fish responses to manipulated microhabitat complexity in urbanised shorelines

“…As degraded habitats and artificial coastal defences typically lack the quantity and range of habitat features normally found in natural shores (Lawrence et al., 2021; Nash et al., 2013, but also see Grasselli & Airoldi, 2021), the creation of microhabitats is an important form of active interventions for biodiversity enhancement (Loke et al., 2015). The various sizes of microhabitats in the Complex fish house were designed to provide more unique niche spaces for fishes compared to the Simple fish house.…”

Do artificial vs natural substrates cause a difference in assemblages of peracarids? A case study in the Western Mediterranean basin

“…Most of the previous studies have pointed out that artificial substrates do not act as natural surrogates (Bulleri & Chapman, 2004;Burt et al, 2009) due to differences in material type, substrate complexity, inclination, orientation and wave exposure among others (Hanlon et al, 2018;Evans et al, 2021;Grasselli & Airoldi, 2021;Hartanto et al, 2022). However, few exceptions have evidenced that artificial substrates are not generally ecologically poor (Gacia et al, 2007;López, 2022;Baxter et al, 2023).…”

“…These new artificial rocky substrates support distinct assemblages, which are generally considered less biodiverse with low ecological value compared to natural rocky marine habitats (Grasselli & Airoldi, 2021;Sedano et al, 2021;Doods et al, 2022). Most studies have focused on comparing community structures between natural and artificial habitats based on differences in material type (Hartanto et al, 2022), substrate complexity (Evans et al, 2021), substrate inclination (Grasselli & Airoldi, 2021) and orientation among others (Hanlon et al, 2018). Generally, these studies have concluded that artificial structures do not function as real surrogates of natural rocky habitats (Bulleri & Chapman, 2004Burt et al, 2009;Sedano et al, 2019).…”

Coastal greening of grey infrastructure: an update on the state-of-the-art

“…Whilst it appears that surface properties may influence microbial communities early on, it appears that communities converge later in the ecological succession process. Other factors, such as site or surface aspect (north-south directionality) and orientation of material (e.g., horizontal/vertical), may have greater influence on community composition (Firth et al 2015;Amstutz et al, 2021Amstutz et al, , 2023, with effects potentially even larger than those from surface complexity (Grasselli and Airoldi, 2021). This evolving picture can help industry focus resources on other aspects of material choice, including carbon footprint (Dennis et al 2018;Dauvin et al 2022) and chemical pollution of concrete (Kress et al, 2002;McManus et al, 2018).…”

“…-Consideration of variability with orientation differences (Grasselli and Airoldi, 2021). Limited metrics measured.…”