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Coastal Management

Do fish communities need natural shorelines, or are artificial structures ok?

Article: Scyphers SB, Gouhier TC, Grabowski JH, Beck MW, Mareska J, Powers SP (2015) Natural Shorelines Promote the Stability of Fish Communities in an Urbanized Coastal System. PLoS ONE 10(6): e0118580. doi:10.1371/journal.pone.0118580

 

All about coastal shorelines

Coastal habitats provide shelter and food for many marine ecosystem communities. Human impact such as shoreline development and pollution, coupled with erosion, have put huge stressors on many marine species. Seawalls and bulkheads have been built along shorelines to help with coastal protection from natural erosion and human development, but can they provide the same needs, primarily shelter and food, that natural vegetated shorelines can for fish communities?

In order to help protect the marine coastal communities, we must first understand how these engineered structures contribute to the safety and welfare of fish populations. Scyphers et al. set out to examine the fish community stability (the capacity for the fish community to absorb perturbations and still function) in reference to the structure of natural landscape coastlines and human engineered coastlines.

fig 1

Fig 1. Example photographs of shoreline types. Photographs of (a) natural, (b) riprap/rubble, (c) vertical wall, and (d) vertical wall with riprap shorelines in the study system.

How they did it

For eleven years (2001-2011) the researchers examined the coastal shorelines of Mobile Bay, Alabama in the Gulf of Mexico. Mobile Bay is the perfect place to analyze the effects of artificial structures as 38% of the bay’s coast has been transformed into vertical walls and revetments and about 98% of the bay is experiencing erosion. Using gillnets, one-hour trolls were conducted monthly to collect adult and juvenile finfish species on the coast of Mobile Bay. Samples included locations of natural (aka vegetated) shorelines, rubble revetments, vertical walls, and vertical walls with riprap (structured rock reinforcements) (Fig. 1).

 

 

 

What they found and why we should care

fig 2

Fig 2. Global wavelet power spectrum of monthly average abundance and species richness by shoreline type.

It was found that natural landscapes supported more stable fish communities than engineered shorelines. This does not, however, mean that all the engineered shorelines behaved the same. Straight rubble and riprap shorelines provided more fish stability than vertical walls, with or without riprap (Fig. 2). This suggests that the structural complexity can be a good thing at times, providing more nooks and crannies for hiding, laying eggs, and protection from waves and surge. Natural habitats are generally pretty complex, providing habitat, food, and nursery grounds to several fish species. Vertical walls on the other hand are not very structurally complex, providing very little in terms of safe havens for fish communities. Therefore, if shoreline development or structuring is necessary, structurally complex edifices should be built, such as rubble walls or ripraps.

While it comes to no surprise that natural environments provide the best habitat for fish communities, this study demonstrates that certain artificial structures are better than others. Mobile Bay has seen an increase in engineered structures due to both natural erosion and coastal developments. Requiring coastal protection is necessary in these locations, but these structurally complex, or not so complex, features only mimic natural habitats and do not fully compensate for the loss of natural habitat.

 

If you had to engineer a shoreline structure to help with erosion, what would you build to best support the fish communities? Let us know in the comments section!

 

 

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