Quantitative Estimates of Bio- Remodeling on Coastal Rock Surfaces The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Citation Pappalardo, Marta et al. "Quantitative Estimates of Bio-Remodeling on Coastal Rock Surfaces." Journal of Marine Science and Engineering 4, 2( May 2016): 37 © 2016 The Author(s) As Published http://dx.doi.org/10.3390/jmse4020037 Publisher MDPI AG Version Final published version Citable link http://hdl.handle.net/1721.1/113360 Terms of Use Creative Commons Attribution Detailed Terms http://creativecommons.org/licenses/by/4.0/ Journal of Marine Science and Engineering Review Quantitative Estimates of Bio-Remodeling on Coastal Rock Surfaces Marta Pappalardo 1,*, Markus Buehler 2, Alessandro Chelli 3, Luca Cironi 1, Federica Pannacciulli 4 and Zhao Qin 2 1 Department of Earth Sciences, Pisa University, Pisa 56126, Italy; [email protected] 2 Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA; [email protected] (B.M.); [email protected] (Q.Z.) 3 Department of Physics and Earth Sciences “M. Melloni”, Parma University, Parma 43100, Italy; [email protected] 4 Marine Environment Research Centre (ENEA)-Santa Teresa P.O., Pozzuolo di Lerici 19100, Italy; [email protected] * Correspondence: [email protected]; Tel.: +39-050-2215748 Academic Editor: Gerben Ruessink Received: 5 March 2016; Accepted: 2 May 2016; Published: 26 May 2016 Abstract: Remodeling of rocky coasts and erosion rates have been widely studied in past years, but not all the involved processes acting over rocks surface have been quantitatively evaluated yet. The first goal of this paper is to revise the different methodologies employed in the quantification of the effect of biotic agents on rocks exposed to coastal morphologic agents, comparing their efficiency. Secondly, we focus on geological methods to assess and quantify bio-remodeling, presenting some case studies in an area of the Mediterranean Sea in which different geological methods, inspired from the revised literature, have been tested in order to provide a quantitative assessment of the effects some biological covers exert over rocky platforms in tidal and supra-tidal environments. In particular, different experimental designs based on Schmidt hammer test results have been applied in order to estimate rock hardness related to different orders of littoral platforms and the bio-erosive/bio-protective role of Chthamalus ssp. and Verrucariaadriatica. All data collected have been analyzed using statistical tests to evaluate the significance of the measures and methodologies. The effectiveness of this approach is analyzed, and its limits are highlighted. In order to overcome the latter, a strategy combining geological and experimental–computational approaches is proposed, potentially capable of revealing novel clues on bio-erosion dynamics. An experimental-computational proposal, to assess the indirect effects of the biofilm coverage of rocky shores, is presented in this paper, focusing on the shear forces exerted during hydration-dehydration cycles. The results of computational modeling can be compared to experimental evidence, from nanoscopic to macroscopic scales. Keywords: bioerosion; bioprotection; rocky coasts; rock hardness; materials science; computational modeling; geomorphology 1. Introduction The influence of biological agents in rocky coastal landforms shaping has been recognized for a long time [1–8]. Virtually, biota may exert a bioerosive, bioprotective, or bioconstructional role on rocky coasts. In this paper, we focus on bioerosional and bioprotective effects of biota on coastal rocks, considering both of them as part of the “bio-remodeling” effect, and discuss the importance of a quantitative understanding of their role. Bioconstructors as well as borers operating on reefs are neglected, as processes and rates are quite different [9]. A valuable quantitative approach to erosion on biogenic rocks is provided by Moses [10]. J. Mar. Sci. Eng. 2016, 4, 37; doi:10.3390/jmse4020037 www.mdpi.com/journal/jmse J. Mar. Sci. Eng. 2016, 4, 37 2 of 21 Due to the high population density in coastal areas and the cost of coastal planning, bio-remodeling represents a relevant problem which has been neglected in the recent literature on coastal management, focused mainly on beach erosion [11]. Providing an updated conceptual model of biotic agency on coastal rocks, Naylor et al.[12] suggest that future research in this field should be aimed at providing quantitative estimates of this process in different contexts, in order to assess its contribution to the global sedimentary budget. In this sense, it is crucial to identify the best methodologies suitable for tackling this issue with a strictly quantitative approach. The aim of this paper is thus to revise the different methodologies employed in the quantification of the effect of biotic agents on rocks exposed to coastal morphologic agents, comparing their efficiency and inferring specific indications useful for the wide community of scientists working in the coastal environment (engineers and, in a broad sense, all environmental scientists). Literature on biotic agents onJ. coastalMar. Sci. Eng. rocks 2016, 4, has37 been revised, focusing on quantitative assessments and on methodological2 of 21 approaches. In some cases, quantification should be considered in a relative sense as, e.g., the estimate of a percentagefocused duemainly to on bioerosion beach erosion of [11]. overall Providing weathering. an updated As conceptual a complement model of biotic for thisagency review, on coastal we provide new androcks, partly Naylor unpublished et al. [12] suggest data, that suggesting future research possible in this field additional should be aimed methodologies, at providing quantitative based both on estimates of this process in different contexts, in order to assess its contribution to the global sedimentary experimentalbudget. and In this computational sense, it is crucial activities. to identify the best methodologies suitable for tackling this issue with a Rockystrictly shorelines quantitative are approach. shaped by a suite of weathering processes (physical, chemical, and biological) that operateThe on aim them, of this reducing paper is thus the to revise resisting the different force methodologies of rock (FR). employed Weathering in the quantification processes of the affect the effect of biotic agents on rocks exposed to coastal morphologic agents, comparing their efficiency and inferring coastal profilespecific indications being scaled useful for in the importance wide community according of scientists to working their in elevation the coastal environment with respect (engineers to mean sea level (seeand, [13 ],in Figurea broad 7.3).sense, Amongall environmental them, bioerosionscientists). Literature and its on counterpart biotic agents on bioprotection coastal rocks has (on been the whole “bio-remodeling”)revised, focusing are recognizedon quantitative as playingassessments a relevantand on methodological role in the intertidalapproaches. andIn some lower cases, midlittoral quantification should be considered in a relative sense as, e.g., the estimate of a percentage due to bioerosion zones [12of], overall but their weathering. efficiency As a complement long- and for cross-shore this review, we still provide needs new to and be partly thoroughly unpublished defined. data, In the midlittoralsuggesting zone, biodiversity possible additional is maximized methodologies, due based to both the on density experimental of biomass and computational colonizing activities. rock surfaces [14]. Here, a varietyRocky of biota shorelines displays are shaped different by a suite activities of weathering on rocks, processes the (physical, rate and chemical, magnitude and biological) of each that depending operate on them, reducing the resisting force of rock (FR). Weathering processes affect the coastal profile being on both ecologicalscaled in importance factors according and environmental to their elevation constraints. with respect to mean sea level (see [13], Figure 7.3). Among Sincethem, the bioerosion term “bioerosion” and its counterpart was bioprotection introduced (on the by whole Neumann “bio‐remodeling”) [1] for the are recognized coastal environment, as playing the contributiona relevant of biota role in to the the intertidal weathering and lower processes midlittoral zones affecting [12], but coastal their efficiency rocks long has‐ beenand cross evaluated‐shore still by many needs to be thoroughly defined. In the midlittoral zone, biodiversity is maximized due to the density of authors. Thebiomass papers colonizing of Schneider rock surfaces [2 ],[14]. Trudgill Here, a variety [4], and of biota Torunski displays [3 different] still represent activities on the rocks, classical the rate reference studies andand constitutemagnitude of theeach fundamentalsdepending on both forecological any bio-process factors and environmental approach constraints. to geomorphological studies of rocky coasts,Since although the term “bioerosion” limited was to limestoneintroduced by shores. Neumann These [1] for the works coastal assessenvironment, the the concept contribution of biological of biota to the weathering processes affecting coastal rocks has been evaluated by many authors. The papers zoning ofof rocky Schneider shorelines, [2], Trudgill i.e.[4], ,and the Torunski distribution [3] still