Chapter 4 Design Options, Implementation Issues and Evaluating Success of Ecologically Engineered Shorelines

Human population growth and accelerating coastal development have been the drivers for unprecedented construction of artificial structures along shorelines globally. Construction has been recently amplified by societal responses to reduce flood and erosion risks from rising sea levels and more extreme storms resulting from climate change. Such structures, leading to highly modified shorelines, deliver societal benefits, but they also create significant socioeconomic and environmental challenges. The planning, design and deployment of these coastal structures should aim to provide multiple goals through the application of ecoengineering to shoreline development. Such developments should be designed and built with the overarching objective of reducing negative impacts on nature, using hard, soft and hybrid ecological engineering approaches. The design of ecologically sensitive shorelines should be context-dependent and combine engineering, environmental and socioeconomic considerations. The costs and benefits of ecoengineered shoreline design options should be considered across all three of these disciplinary domains when setting objectives, informing plans for their subsequent maintenance and management and ultimately monitoring and evaluating their success. To date, successful ecoengineered shoreline projects have engaged with multiple stakeholders (e.g. architects, engineers, ecologists, coastal/port managers and the general public) during their conception and construction, but few have evaluated engineering, ecological and socioeconomic outcomes in a comprehensive manner. Increasing global awareness of climate change impacts (increased frequency or magnitude of extreme weather events and sea level rise), coupled with future predictions for coastal development (due to population growth leading to urban development and renewal, land reclamation and establishment of renewable energy infrastructure in the sea) will increase the demand for adaptive techniques to protect coastlines. In this review, we present an overview of current ecoengineered shoreline design options, the drivers and constraints that influence implementation and factors to consider when evaluating the success of such ecologically engineered shorelines

Loss and Recovery Potential of Marine Habitats: An Experimental Study of Factors Maintaining Resilience in Subtidal Algal Forests at the Adriatic Sea

BACKGROUND: Predicting and abating the loss of natural habitats present a huge challenge in science, conservation and management. Algal forests are globally threatened by loss and severe recruitment failure, but our understanding of resilience in these systems and its potential disruption by anthropogenic factors lags well behind other habitats. We tested hypotheses regarding triggers for decline and recovery potential in subtidal forests of canopy-forming algae of the genus Cystoseira. METHODOLOGY/PRINCIPAL FINDINGS: By using a combination of historical data, and quantitative in situ observations of natural recruitment patterns we suggest that recent declines of forests along the coasts of the north Adriatic Sea were triggered by increasing cumulative impacts of natural- and human-induced habitat instability along with several extreme storm events. Clearing and transplantation experiments subsequently demonstrated that at such advanced stages of ecosystem degradation, increased substratum stability would be essential but not sufficient to reverse the loss, and that for recovery to occur removal of the new dominant space occupiers (i.e., opportunistic species including turf algae and mussels) would be required. Lack of surrounding adult canopies did not seem to impair the potential for assisted recovery, suggesting that in these systems recovery could be actively enhanced even following severe depletions. CONCLUSIONS/SIGNIFICANCE: We demonstrate that sudden habitat loss can be facilitated by long term changes in the biotic and abiotic conditions in the system, that erode the ability of natural ecosystems to absorb and recover from multiple stressors of natural and human origin. Moreover, we demonstrate that the mere restoration of environmental conditions preceding a loss, if possible, may be insufficient for ecosystem restoration, and is scarcely cost-effective. We conclude that the loss of complex marine habitats in human-dominated landscapes could be mitigated with appropriate consideration and management of incremental habitat changes and of attributes facilitating system recovery

Variations in recruitment patterns throughout the reproductive season:

<p>Average densities (±1SE, n = 5 plots of 30×30 cm) of <i>C. barbata</i> recruits in plots cleared in March 2009 (beginning of reproductive season, T1 in black), vs. plots cleared in May 2009 (end of the reproductive season, T2-in blue), at La Vela (LV-triangles) and Due Sorelle (DS-squares) from July 2009 to February 2010. There were un-manipulated control plots (C-in purple) at both clearing times and sites, but all had virtually no recruits and thus the points in the graph overlap. All the plots were located in shallow areas where canopies of <i>C. barbata</i> are present.</p

Map of the study region: superimposed is the known distribution of <i>Cystoseira</i> canopies until 2001 (light green, from: [40]) and since 2006 (dark green, data from the present work).

<p>Map of the study region: superimposed is the known distribution of <i>Cystoseira</i> canopies until 2001 (light green, from: <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0010791#pone.0010791-Fabi1" target="_blank">[40]</a>) and since 2006 (dark green, data from the present work).</p

Wave regime at the study region:

<p><b>A</b>. Number of sea storms (significant wave height H_s >3.5 m) and <b>B</b>. maximal wave height recorded each year from 1999–2004 by a waver recording buoy located just offshore the study sites (43.49.47 N; 13.42.52 E). Data are from APAT through the RON (Rete Ondametrica Nazionale) network (courtesy Dr. G. Nardone).</p

Natural changes in cover of recruits:

<p>Average percent cover (±1SE, n = 3 plots of 30×30 cm) of <i>C. barbata</i> recruits on large (>4 m³, L-black) vs. small (>1 m³, S-blue) marked boulders from July 2008 to February 2009 at Due Sorelle (squares) and La Vela (triangles).</p

Results from the transplantation experiments:

<p><b>A</b>.<b>–B</b>. Average percent <b>Survival</b> and <b>C</b>.<b>–D</b>. average <b>Size</b> of <i>C. barbata</i> juveniles transplanted at each study site from July 2008 to February 2009. Treatments were transplanted to: horizontal substrata surrounded by adults (green), horizontal substrata without adults (black), vertical substrata without adults (blue) and original unstable control substrata (purple). Data are averages ±1 SE (n = 4 plots for survival, in each plot n = 5 juveniles initially and thereon the number varied depending on the number of surviving juveniles). Superimposed circles represent results of SNK test for survival data at Feb. 09 in La Vela. Size of natural (non-transplanted, n = 80) recruits at each site is also presented (red). As all plots at Due Sorelle were destroyed by the last monitoring point due to storms, thus size data for this site are presented only until Oct 08.</p

Photos of the Clearing Experiment:

<p><b>A</b>. un-manipulated (control) plot showing typical cover of stable habitats composed of various (non-<i>Cystoseira</i>) seaweeds, mussel beds and turf. <b>B</b>. Representative close-up of control plot with no <i>Cystoseira</i> recruits. <b>C</b>. Cleared plot dense ca. 3 m old <i>C</i>. <i>barbata</i> recruits. <b>D</b>. Close-up of ca. 3 m old <i>C</i>. <i>barbata</i> recruits in cleared plot.</p