Course:EOSC270/2021/Impacts of Shoreline Armoring on Marine Ecosystems

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Shoreline Armoring

Shoreline Armoring, also referred to as Coastal Development, is the process of building robust structures next to the ocean in shoreline communities to prevent the natural process of erosion from occurring.[1] Erosion occurs naturally and is when water levels and wave action cause the breakdown of larger sediment into smaller ones and is a major process which causes changes in the sediment profile of the intertidal zone. Over time, the composition and structure of a certain intertidal zone will naturally change too, leading to differences in the length and depth of the intertidal zone and changes in water currents near the coast. Erosion can also lead to changes in the sediment and ground of the terrestrial zone right above the intertidal zone.[2]

Figure 1: A seawall protecting the ruins of an old priory in Ireland
Figure 2: Groins on a beach in Poland

Shoreline armoring is conducted near oceanic ecosystems since erosion can cause buildings or other infrastructure near the shore to collapse or get damaged. This occurs since erosion will break down larger sediments into smaller ones, leading to a disruption in the foundation of buildings near the shore.[3] Shoreline armoring is not only meant for housing communities, but also utilized for all types of infrastructure in proximity to the oceanic shoreline, where buildings next to the shoreline have seen a very large increase in demand in recent years, leading to an increase in the amount of shoreline armoring being performed.[4]

How Shoreline Armoring is Conducted:

Figure 3: An offshore Breakwater in Plymouth, England

Shoreline armoring can occur in a multitude of forms where the two major methods of shoreline armoring are to either prevent or reduce wave action on the sediment, or to prevent the displacement of sediment that occurs with erosion. Shoreline armoring includes structures such as: Seawalls, Bulkheads (see Figure 1), Groins (see Figure 2) and Breakwaters (see Figure 3). Structures such as Seawalls and Bulkheads are wall-like structures, placed between sediment and ocean to protect the land from wave action and prevent sediment that is behind the wall from escaping into the ocean. Breakwaters are structures usually placed offshore to disrupt wave action, making the erosion process much slower. Groins are structures which prevent sediment from being transported in longshore sediment transport.[5] Longshore transport is the transport of sediment either up or down the shoreline by natural processes such as wind and currents.[6]

Significance of Shoreline Armoring:

Shoreline armoring is a very significant process for the human society as it protects man-made structures on land from the ever-changing intertidal sediment and wave-action. This does however mean that the organisms living in said intertidal zones are subjected to a disruption in their ecosystem, which can cause any number of unexpected outcomes, some of which are discussed below. Since shoreline armoring disrupts these naturally occurring phenomena, it is very important to plan and execute the construction of shoreline armoring structures with uttermost respect for the marine life in nearby ecosystems, as to not start a cascade of actions leading to a larger environmental problem than there was initially.

The Impacts of Shoreline Armoring on Marine Ecosystems

How Shoreline Armoring Affects Marine Ecosystems

The construction of protective structures along coastlines serves the purpose of preserving urban development, such as sea-side communities. Despite its efficiency, the presence of the man-made structures in question applies pressure to the dynamic nature of intertidal and soft sediment ecosystems, which subsequently leads to adverse ecological effects. Shoreline armoring is one of the most prevalent methods of coastal urbanization that causes the deterioration and erosion of coastal beaches, therefore interfering with the intertidal or soft-sediment communities that rely on these habitats.

Physical Impacts

The physical influences of shoreline armoring on estuarine habitats are immediate and therefore more obvious to detect. One example of a direct and physical consequence resulting from shoreline armoring would be placement loss, which entails the decay of shoreline habitats directly caused by the base of the structures. The deflection of wave energy causes erosion which reduces necessary surface area for nearshore and intertidal habitats. Furthermore, the intrusion of man-made structures on shorelines conflicts with the hydrodynamics of the aquatic environment, shifting the dynamics of soft sediments and altering water flow. [7] Such abrupt changes in the physical aspects of marine ecosystems result in adverse effects on shore-bound flora and fauna.

Ecological Impacts

In contrast, generalized ecological responses to shoreline armoring have been more difficult to detect and harder to monitor since most of the studies conducted about this issue occur in individualized specific marine ecosystems. [8] The data collected from the studies conducted shows that direct physical stressors that result from shoreline armoring have secondary effects such as decreasing water quality, the introduction of invasive species, shifts in species’ distribution, changes to the connectivity of shoreline habitats, etc. [9]

For example, the reduction of coastline habitats simultaneously leads to the disappearance of vegetation along shorelines. Furthermore, the lack of shading from the intertidal flora and reduced moisture retention on the surface coastal structures results in temperature changes which may eventually conflict with the biotic requirements of some intertidal species. Therefore it is highly probable that shoreline species’ abundances will lower over time since some coastal fauna may have utilized the vegetation found on shorelines as refuge from predators and the abiotic requirements of others may have needed the temperature to remain the same as it was before the introduction of shoreline structures. [9]

Figure 4: Sea turtles on the beach

Another example is the disruption of habitat connectivity due to shoreline armoring decreasing the width of the intertidal transition zone due to the lowering elevation between terrestrial and marine habitats. In addition, armored coastlines have a smaller proportion of wrack in comparison to unarmored coastlines in beach areas and within the transition zone. This leads to decreases in biodiversity and ecosystem function due to lower numbers of wrack consumer species. [10]

The Effects of Shoreline Armoring on Sea Turtles

Since shoreline armoring introduces unanticipated physical alterations to coastline environments, species that rely on these areas as their habitat end up being impacted. One example is the construction of shoreline armoring structures on the nesting beaches of sea turtles blocking access to ideal nesting habitats. Restricting access to upper beaches reduces the distribution of sea turtle nests along coasts because of the lack of remaining space left behind on beaches. The deflected wave energy from the forefront of sea walls results in lowering of the beach and erosion, therefore adding to the stress caused by tropical storms in season. Therefore, since the eggs are forced to hatch in lower beach areas closer to shore, there is an increased risk of egg mortality. [11]

Measurable Impacts of Shoreline Armoring on the Ecosystem

Figure 5. How shoreline armoring affects the width of beach available

Historical impacts:

While land can be temporarily protected from being lost to the sea with the use of shoreline armoring structures, over time they can have the unintended side effect of actually speeding up the loss of coastal habitats and beaches on the side of the shoreline armoring structure that is towards the sea.[12]

In Figure 5 we can see an example of one of the mechanisms by which the amount of shoreline available to us and the local wildlife is reduced. The installation of the seawall not only eats into the width of the beach in and of itself, it also prevents the beach from retreating, causing the beach to get narrower and narrower from erosion until eventually there is no beach left, just water all the way up to the seawall.[12]

Present status:

Moving forward to the present day we can see these unintended side effects mentioned above become fully realized. In areas where shoreline armoring structures are built, Intertidal and mid beach zones are narrower while the zones from the drift line to the upper beach limit were completely gone. As a result of this, there is noticeably less biodiversity due to the significant reduction in habitable area from beach loss. In the upper intertidal zone of shorelines with shoreline armoring structures, the amount and size of invertebrates is significantly lower when compared to unarmored shorelines. In addition to this the species richness and abundance of foraging shorebirds and roosting birds was significantly lower on armored segments of the shore than unarmored ones.[13]

In addition to these, other physical processes are affected as well, such as causing the sediment to coarsen and the amount of organic input to decrease. Coarser sediment tends to be less hospitable for most organisms due to it being less effective at retaining nutrients, and the decrease in organic input amplifies this problem.[14]

Projections for the future:

Due to the fact that the construction of shoreline armoring structures oftentimes causes increased erosion on neighboring areas, more likely than not even more shoreline armoring structures will need to be built adjacent to the original one, further spreading out and exacerbating all the problems outlined above. With the increasingly volatile nature of the tides, sea levels and weather we will probably see more and more shoreline armoring structures be built, causing us to slowly run out of useable shorelines, both for us and for the wildlife that inhabits these areas of land lost to the sea.[15]

Studies have shown that softer approaches can be helpful in minimizing the impacts of shoreline armoring on the environment, for example, building structures that slow down the flow of water instead of completely halting it. Shorelines should be given sufficient leeway to adapt to changes in tides and be able to retreat inland to preserve the shore.[7]

Protecting Marine Ecosystems

Local Solutions

Community Planning

Figure 6. Example of a living shoreline to protect against coastal erosion

In order to protect coastal ecosystems from habitat loss due to shoreline armoring, different approaches to tackling erosion could serve to minimize damage. Community planners making decisions about how to preserve coastal properties can consider solutions that are more natural and not as intrusive as traditional human-made structures. One option is to choose human-made structures that mimic natural ecosystems, such as rubble instead of harsh vertical walls.[16] This serves as a low-level adjustment of coastal protection that could demonstrate improvements in marine conservation.

Implementing “living shorelines” (as seen in Figure 6) could be a more effective alternative, where native vegetation is planted to maintain the infrastructure of the coastline while also provisioning ecosystem services within local habitats.[17] These plans do not harshly truncate the intertidal area, and instead provide sediment reinforcement to protect against wave action.[18]

This responsibility does not only lie with community planners. Studies suggest that homeowners along the shoreline have power to affect change in their neighbourhoods by choosing options that benefit both the property owners as well as the ecosystems in which they reside.[19] Actions taken by individual homeowners have been shown to have cascading effects through their communities, where the decision of one neighbor to construct armoring structures on their property directly influences other community members to take the same action—sometimes due to the damage caused by the installation of the first armoring structure.[20]

Policy and Regulation

Policies and regulatory institutions also contribute to the maintenance of coastal shores. In many parts of the world, regulation occurs at many levels, including federal, state, provincial, municipal, and local. For example, in the United States, projects are subject to regulation via policies such as the Clean Water Act as well as state coastal regulatory departments and often local planning permit programs.[21] Science-based coordination among governmental and non-governmental regulatory institutions can serve to make the process of shoreline protection easier, from initial planning and design through to continuous maintenance, whereas many shores currently fall under several different jurisdictions with competing priorities.[22] Ecologically based models for coastal environments that are enforced through regulation can provide better protection for marine organisms.

Figure 7. Restored shoreline before and after conversion from an eroded, hard shoreline

Restoration

Restoration efforts have also been seen around the world, aiming to revitalize coastal habitats after degradation. The removal of shoreline armoring structures (see Figure 7) can allow for ecosystems to stabilize and lead to increased biological functioning after a period of recovery, demonstrating another avenue to pursue in protecting coastal environments.[23] Coastal restoration projects can have varying levels of success, commonly being applied to semi-enclosed areas such as coastal bays and estuaries, with more open ecosystems often proving more difficult to restore and protect if exposed to stressors and disturbances outside of armoring.[24] Proper restoration techniques must be utilized in order to minimize unintended damage after the removal of shoreline armoring structures.

Global Solutions

To aid in the acceptance and implementation of living shorelines, communal efforts should be made globally to spread awareness about the ecological benefits of this alternative to armoring, through which marine habitats can be better protected. Economic benefits of coastal preservation may also serve as an incentive to move away from traditional shoreline armoring, as coastlines are very productive habitats that provide food for human and non-human organisms alike and also capture atmospheric carbon that otherwise contributes to global climate change.[25] When shorelines are artificially modified too much, these habitats and important ecological processes are degraded and are unable to store as much carbon, losing ecological and economic value.[25]

Worldwide consideration of these societal benefits should be bolstered in order to encourage sufficient marine conservation attempts.[17] Local solutions may be viable in a broad range of locations and circumstances around the world, and thus may prove to offer a path forward to protect coastal ecosystems.[26]

References

  1. ↑ "What is shoreline armoring?". National Oceanic and Atmospheric Administration. 2013, June 01. |first= missing |last= (help); Check date values in: |date= (help)
  2. ↑ Griggs, Gary B. (2010). "The Effects of Armoring Shorelines—The California Experience" (PDF). U.S. Geological Survey Scientific Investigations Report. 2010-5254: 77–88.
  3. ↑ Dean, R.G (1986). "COASTAL ARMORING: EFFECTS, PRINCIPLES AND MITIGATION". Coastal Engineering. 20: 1843–1857.
  4. ↑ Landry, Craig E.; Keeler, Andrew G.; Kriesel, Warren (2003). "An Economic Evaluation of Beach Erosion Management Alternatives". Marine Resource Economics. 18–2: 105–127.
  5. ↑ Ford-Martin, Paula Ann (2021). "Shoreline Armoring". Retrieved January 13 2021. Check date values in: |access-date= (help)
  6. ↑ Seymour, Richard J. (2005). Schwartz, M.L (ed.). Encyclopedia of Coastal Science. Springer, Dordrecht. p. 600. ISBN 978-1-4020-3880-8.
  7. ↑ 7.0 7.1 Dugan, J., Emery, K., Alber, M., Alexander, C., Byers, J., & Gehman, A. et al. (2017). Generalizing Ecological Effects of Shoreline Armoring Across Soft Sediment Environments. Estuaries And Coasts, 41(S1), 180-196. doi: 10.1007/s12237-017-0254-x
  8. ↑ Morley, Sarah A. (2012). "Ecological Effects of Shoreline Armoring on Intertidal Habitats of a Puget Sound Urban Estuary". Estuaries and Coasts. 35: 774–784 – via Springerlink. line feed character in |title= at position 55 (help)
  9. ↑ 9.0 9.1 Prosser, Diann J. (2017). "Impacts of Coastal Land Use and Shoreline Armoring on Estuarine Ecosystems: an Introduction to a Special Issue". Estuaries and Coasts – via Springer. line feed character in |title= at position 51 (help)
  10. ↑ Heerhartz, Sarah M. (December 2013). [10.1007/s12237-013-9754-5 "Effects of Shoreline Armoring on Beach Wrack Subsidies to the Nearshore Ecotone in an Estuarine Fjord"] Check |url= value (help). Estuaries and Coasts. 37: 1256–1268 – via Springer. line feed character in |title= at position 55 (help)
  11. ↑ Witherington, Blair (2011). [www.elsevier.com/locate/jembe "Sea turtle responses to barriers on their nesting beach"] Check |url= value (help). Journal of Experimental Marine Biology and Ecology. 401: 1–6 – via Elsevier.
  12. ↑ 12.0 12.1 Melius, M., & Caldwell, M. (2015). 2015 CALIFORNIA COASTAL ARMORING REPORT: Managing Coastal Armoring and Climate Change Adaptation in the 21st Century (pp. 8-11). Stanford Law School. Retrieved from https://law.stanford.edu/wp-content/uploads/2015/07/CalCoastArmor-FULL-REPORT-6.17.15.pdf
  13. ↑ Dugan, J., & Hubbard, D. (2010). Puget Sound Shorelines and the Impacts of Armoring— Proceedings of a State of the Science Workshop, May 2009 (pp. 187-194). Tacoma Publishing Service Center. Retrieved from https://pubs.usgs.gov/sir/2010/5254/pdf/sir20105254.pdf
  14. ↑ Ruggiero, P. (2010). Puget Sound Shorelines and the Impacts of Armoring—Proceedings of a State of the Science Workshop, May 2009 (pp. 179-186). Tacoma Publishing Service Center. Retrieved from https://pubs.usgs.gov/sir/2010/5254/pdf/sir20105254.pdf
  15. ↑ O'Connell, J. (2010). Puget Sound Shorelines and the Impacts of Armoring—Proceedings of a State of the Science Workshop, May 2009 (pp. 65-76). Tacoma Publishing Service Center. Retrieved from https://pubs.usgs.gov/sir/2010/5254/pdf/sir20105254.pdf
  16. ↑ Scyphers, S. B., Gouhier, T. C., Grabowski, J. H., Beck, M. W., Mareska, J., & Powers, S. P. (2015a). Natural shorelines promote the stability of fish communities in an urbanized coastal system. Plos One, 10(6), e0118580. doi:10.1371/journal.pone.0118580
  17. ↑ 17.0 17.1 Davis, J. L., Currin, C. A., O'Brien, C., Raffenburg, C., & Davis, A. (2015). Living shorelines: Coastal resilience with a blue carbon benefit. Plos One, 10(11), e0142595. doi:10.1371/journal.pone.0142595
  18. ↑ Scyphers, S. B., Beck, M. W., Furman, K. L., Haner, J., Keeler, A. G., Landry, C. E., . . . Grabowski, J. H. (2020). Designing effective incentives for living shorelines as a habitat conservation strategy along residential coasts. Conservation Letters, 13(5), e12744. doi:https://doi.org/10.1111/conl.12744
  19. ↑ Scyphers, S. B., Picou, J. S., & Powers, S. P. (2015b). Participatory conservation of coastal habitats: The importance of understanding homeowner decision making to mitigate cascading shoreline degradation. Conservation Letters, 8, 41–49. doi: 10.1111/conl.12114
  20. ↑ Gittman, R. K., Fodrie, F. J., Popowich, A. M., Keller, D. A., Bruno, J. F., Currin, C. A., . . . Piehler, M. F. (2015). Engineering away our natural defenses: An analysis of shoreline hardening in the US. Frontiers in Ecology and the Environment, 13(6), 301-307. doi:https://doi.org/10.1890/150065
  21. ↑ Pace, N. L. (2017). Permitting a living shoreline: A look at the legal framework governing living shoreline projects at the federal, state, and local level. In D. M. Bilkovic
, M. M. Mitchell
, M. K. La Peyre
 & J. D. Toft (Eds.), (1st ed., pp. 33-50) Routledge. doi:10.1201/9781315151465-5
  22. ↑ Bilkovic, D. M., Mitchell, M., Mason, P., & Duhring, K. (2016). The role of living shorelines as estuarine habitat conservation strategies. Coastal Management, 44(3), 161-174. doi:10.1080/08920753.2016.1160201
  23. ↑ Toft, J. D., Cordell, J. R., & Armbrust, E. A. (2014). Shoreline armoring impacts and beach restoration effectiveness vary with elevation. Northwest Science, 88(4), 367-375. doi:10.3955/046.088.0410
  24. ↑ Elliott, M., Burdon, D., Hemingway, K. L., & Apitz, S. E. (2007). Estuarine, coastal and marine ecosystem restoration: Confusing management and science – A revision of concepts. Estuarine, Coastal and Shelf Science, 74(3), 349-366. doi:10.1016/j.ecss.2007.05.034
  25. ↑ 25.0 25.1 Irving, A.D., Connell, S.D., Russell, B.D. (2011). Restoring coastal plants to improve global carbon storage: Reaping what we sow. PLoS ONE 6(3): e18311. https://doi.org/10.1371/journal.pone.0018311
  26. ↑ Smith, C. S., Gittman, R. K., Neylan, I. P., Scyphers, S. B., Morton, J. P., Joel Fodrie, F., . . . Peterson, C. H. (2017). Hurricane damage along natural and hardened estuarine shorelines: Using homeowner experiences to promote nature-based coastal protection. Marine Policy, 81, 350-358. doi:https://doi.org/10.1016/j.marpol.2017.04.013
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