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

Ferrante Grasselli,Laura Airoldi

doi:10.3389/fmars.2021.766903

Ferrante Grasselli, Laura Airoldi

Open Access

https://doi.org/10.3389/fmars.2021.766903

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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.

Highlights

Urban waterfronts are replete with hard built infrastructure for coastal protection, trade, transportation, and recreation
While in the past there was little ecological consideration as to how marine artificial infrastructure was built (Airoldi et al, 2005), the trend is to look for “greener” designs inspired by or mimicking nature, that introduce less alterations to the natural environment, support wildlife, or recover critical ecosystem functions (Firth et al, 2014b; Dafforn et al, 2015; Airoldi et al, 2021). These greening efforts have had a strong focus on physical habitat structure as a key factor for enhancing natural communities (Loke et al, 2015; Morris et al, 2017)
We removed any species from the plots, as we focused on the physical structure of the primary substrata

Summary

Introduction

Urban waterfronts are replete with hard built infrastructure for coastal protection, trade, transportation, and recreation (e.g., seawalls, jetties, breakwaters, groins, docks, pontoons; Airoldi and Beck, 2007) This infrastructure comes in a variety of designs, materials and spatial configurations, depending on the primary function (Firth et al, 2016). While in the past there was little ecological consideration as to how marine artificial infrastructure was built (Airoldi et al, 2005), the trend is to look for “greener” designs inspired by or mimicking nature, that introduce less alterations to the natural environment, support wildlife, or recover critical ecosystem functions (Firth et al, 2014b; Dafforn et al, 2015; Airoldi et al, 2021) These greening efforts have had a strong focus on physical habitat structure as a key factor for enhancing natural communities (Loke et al, 2015; Morris et al, 2017). A recent meta-analysis has shown that these enhancements often increased the abundance and number of species, yet the outcomes were inconsistent across species and studies, with overall uncertain benefits (Strain et al, 2018b)

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