Local-scale characteristics of high-marsh communities next to developed and undeveloped shorelines in an ocean-dominated estuary, Murrells Inlet, SC

Abstract

Anthropogenic alteration of terrestrial shorelines can have pronounced effects on marine environments at the upland-marsh boundary. Possible terrestrial development effects on several physical and biological variables of high-marsh habitats were examined along developed and undeveloped shorelines in an ocean-dominated, southeastern US estuary. Analyses of sediment characteristics suggested development of the upland boundary affected physical conditions within the high-marsh. For example, pore water salinities were greater along undeveloped shorelines during a non-drought period even after rain events. Significant floral and faunal differences also existed between shoreline treatments. Black needle rush stems were significantly taller and marsh periwinkle densities significantly greater, but eastern coffee bean snail densities were significantly reduced along developed shorelines. Benthic infaunal community abundance and composition also were significantly different between shoreline treatments with sand fly larvae, human pest precursors, either only present or present in greater densities along developed shorelines. Sediment respirometry experiments indicated significant differences in heterotrophic and autotrophic processes occurring between shoreline treatments. Greater sediment surface temperatures along developed shorelines provided one possible mechanism driving high-marsh responses to boundary alteration. The history and extent of shoreline development along with a tendency in ocean-dominated southeastern marshes to resist change likely influenced current ecological conditions within our high-marsh study areas. A greater understanding of the driving mechanisms producing localized effects on salt marshes and recognizing regional differences in marsh resistance to change will facilitate predictions of shoreline development consequences and help in proposing effective management strategies for coastal boundaries.

Effects of Small-Scale Armoring and Residential Development on the Salt Marsh-Upland Ecotone

“…Variance is reported for the random variable of station, sampling point along the transect (2, 4, or 8 m from the upland) nested in station, and βcoefficients are reported for the fixed variables. Significant coefficients are indicated by * (i.e., p < 0.05) northeastern US (Silliman and Bertness 2004;Walters et al 2010). Armoring could ameliorate this effect by blocking water flow paths from the upland to the marsh or by decreasing runoff from the upland by reducing the land-surface gradient adjacent to the marsh.…”

“…Second, the southeastern US coastline is relatively undeveloped (Crossett et al 2005;Gittman et al 2015). Thus, the southeast may not yet exhibit the cumulative effects of development that are present in highly developed coastal regions like New England (Walters et al 2010). Third, we standardized the selection of bulkheads in our study, sampling only at structures that had not obviously reclaimed upland from the marsh.…”

“…Few studies have examined how the more commonplace, low-density residential development and more modest types of shoreline armoring affect coastal marsh habitats (Walters et al 2010;Bozek and Burdick 2005). Small-scale forms of armoring, such as bulkheads, are commonly used to protect single-family homes that are adjacent to salt marshes in the southeastern US.…”

“…These types of structures are typically about 1 m tall and located at or just above the high-tide line. The few studies of modest armoring in low-density residential developments have typically found few or very subtle effects rather than large effects, with effects concentrated in the high marsh (Bozek and Burdick 2005;Walters et al 2010). These studies, however, may have suffered from limited replication (four to five pairs of developed and control sites) and only considered one type of development.…”

“…However, development intensity is substantially lower in the southeast and the marshes are larger, so it is unclear whether results from the northeast can be extrapolated to the US east coast as a whole. The small amount of work that has been conducted in the southeastern US suggests that, in fact, these marshes show subtler and different responses to development than do those in New England (Walters et al 2010). The southeastern US coast is projected to have the highest rate of human population growth from 2010 to 2020 in the coastal US (Crossett et al 2005;Bamford 2013), so it is important both to understand impacts of current coastal development and predict the effects of more intense, future development in this area.…”