This paper titled ‘Ecological Consequences of Shoreline Hardening: A Meta-Analysis’ by Gittman et al. has been published by Oxford University Press on behalf of the American Institute of Biological Sciences in 2016
Review of Scholarly Article ‘Ecological Consequences of Shoreline Hardening: A Meta-Analysis’
We’ve found this recently published paper very relevant to the situation we are facing on the east coast of Bangladesh, where the authorities are building a coastal road dubbed as ‘Marine Drive’, so we’d love to put some notes on the scholarly article here on this blog.
This paper titled ‘Ecological Consequences of Shoreline Hardening: A Meta-Analysis’ by Gittman et al. has been published by Oxford University Press on behalf of the American Institute of Biological Sciences in 2016.
One of the major concerns of marine conservationists is that as the population grows rapidly, particularly in coastal areas, there are demands for engineered shore protection and shoreline hardening. But the increase of shoreline protection structures is predicted to be the reason behind the loss of biodiversity and ecosystem services along the shorelines. The authors designed the study to find out if this hypothesis is true.
For this purpose, the authors conducted a systematic review and meta-analysis of previous studies to compare the ecosystem services, biodiversity and organism abundance along shorelines with and without shoreline protection structures. Three types of structures were considered in this study: (1) seawalls and bulkheads which are vertical walls constructed parallel to shore in or above the high intertidal zone, (2) riprap revetments which are shore-parallel, sloped structures constructed of unconsolidated rock or rubble in or above the high intertidal zone, and (3) breakwaters and sills which are low intertidal or sub-tidal zones are referred to as breakwaters.
Among the 32 studies included in the analyses, 78% were evaluated seawalls, 28% riprap revetments, and 25% evaluated breakwaters. Most studies were conducted in the Atlantic and Gulf of Mexico coasts of the United States. All of the studies were published since 2000, with nearly half of them published since 2010; this indicates that the collected information on the shoreline transformation is very recent.
Will there be any beach left for sea turtles to nest after Bangladesh build a coastal road along its entire eastern coast?
The result shows that seawalls have clear negative effects on coastal biodiversity and habitat quality: reduce 23% biodiversity and 45% organisms of the shorelines. In contrast, riprap or breakwater in the studies analyzed did not affect the biodiversity and abundance of organisms in shorelines much. However, this lack of difference may due to the heterogeneous effects of riprap or breakwaters across organism groups; or because of the small number of studies.
Gittman et al. conclude that the type, structure complexity, composition, and placement of shoreline hardening can have different impacts on the habitat value and functioning of nearshore ecosystems. Some of the main analyses are that: seawalls, with their vertical profile and typically uniform surface, do not offer the same refuge for nekton as boulders and camouflaging sediment or dense marsh vegetation. In contrast, both riprap and breakwaters may provide nekton with equivalent or greater refuge from predation or access to food resources because they typically consist of piles of unconsolidated rock and rubble of varying sizes and shapes. Besides, some shore-protection structures may serve as surrogate habitats for native epibiota where natural hard substrates, such as oyster reefs and mussel beds, have been lost to over-harvest, erosion, and poor water quality. However, the introduction of some types of hard substrates into soft-sediment and biogenic shorelines may also promote invasive species. Therefore, the location relative to invasion pathways and substrate type should be carefully considered. In addition, the construction of seawalls and to a lesser extent, a riprap revetment, can disrupt the connection between upland and intertidal habitat, reflect wave energy and alter sediment transport, and escalate the depth of the intertidal and nearshore subtidal zones. These effects can alter the vegetation nearshore thus disrupt nutrient cycling and reduce pollutant filtration of the ecosystem.
In closing, they recommend coastal managers and decision-makers to consider all those ecological impacts when developing coastal shoreline policies and approving shoreline protection structures. They suggest it is better to use natural alternatives such as living or nature-based shore protection or biogenic habitat restoration which can reduce erosion while also enhancing other ecosystem services.
The authors admit that the study still has some limitations such as the significant heterogeneity across different shores, organism groups, or structure types; the small number of the studies; and lack of time series data in some studies.
For me, the interesting points I found out from reading this study is that the method of this study, systematic review, and meta-analysis, have some advantages as well as disadvantages. We can examine the effects of shoreline protection structures based on the result of previous studies, thus we don’t have to actually conduct research on the field but still can obtain a general picture of these structures in different case studies, at a different location.
However, they can be very heterogeneous and some studies might not maintain their measurements or sampling through time, thus the data is not absolutely reliable and uniform in all studies. The second interesting point for me is that not all engineered shoreline protection structures are harmful to shoreline biodiversity and ecosystems, sometimes they can be beneficial, depending on the type and location of the structures. Therefore, we should study the effects of the structures before installing them. However, after all, it is better to use natural alternatives which can protect the shore as well as prevent potential harm to the ecosystem.
Gittman, R. K., Scyphers, S. B., Smith, C. S., Neylan, I. P., & Grabowski, J. H. (2016). Ecological consequences of shoreline hardening: a meta-analysis. BioScience, biw091.
Tien Huynh is a member of the TeamTurtle; a volunteer Field Assistant for the 2016-17 season. She studies Environmental Science and Management at Asian Women University.