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GCE III - Key Finding in 2017

    Ecological responses to shoreline armoring

    Shoreline structures, from seawalls to sills, are found in coastal ecosystems around the world. However, there have been few studies of their ecological effects, and most of these have been conducted in specific settings. GCE researchers participated in a cross-site effort with investigators from SBC, PIE and VCR aimed at characterizing ecological responses to armoring across the wide diversity of coastal settings where these structures are used. Dugan et al. (2017) set forth a conceptual model that categorized projects according to their purpose (to slow or completely stop the flow of water) and the hydrodynamic energy of the environment (Fig. 1). They predicted greater negative ecological effects for structures designed to stop water flow and for those found in high-energy environments. They then did a literature review of available information on six categories of ecological effects of shoreline armoring habitat distribution, species assemblages, trophic structure, nutrient cycling, productivity, and connectivity across the range of soft sediment environments, from protected harbors to open water beaches. Out of 88 studies, 71% of the effects were significantly negative, 22% were significantly positive, and 7% were not significant. Negative responses were more frequent when structures were intended to stop water flow, as predicted. Trends across the hydrodynamic energy axis were less clear-cut but do suggest intensifying ecological effects with increasing energy. In keeping with this, Gehman et al. (2017) observed subtle effects of bulkheads placed in low energy salt marshes in coastal Georgia. Marshes adjacent to bulkheads had lower elevations than those adjacent to unarmored or forested sites, with greater Spartina coverage and crab burrow abundance. Both of these papers are part of a special issue of Estuaries and Coasts on Shoreline/Land Use Effects.


    Fig. 1 Left: Conceptual model showing predicted ecological impacts in soft sediment environments across the array of shoreline armoring types used to either slow or stop water flow(x-axis) and with different hydrodynamic energy levels at the armoring structure (y-axis). Ecological impacts are predicted to increase as one moves up and to the right within the parameter space. Right: Ecological effects on habitat distribution reported in studies included in shoreline literature review. The histograms correspond to the six combinations of potential effects of an armoring structure on water flow and the hydrodynamic energy of the environment represented by the boxes in the conceptual model (left). In the histogram for each box, the number of significantly positive (green), negative (red), and not significant (NS, gray) observations is plotted. From Dugan et al. 2017.


This material is based upon work supported by the National Science Foundation under grants OCE-9982133, OCE-0620959, OCE-1237140 and OCE-1832178. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.