Barrier islands: coupling anthropogenic stability with ecological sustainability.(Report)

ABSTRACT

Barrier islands provide a host of critical ecosystem services to heavily populated coastal regions of the world, yet they are quite vulnerable to ongoing sea level rise and a potential increase in the frequency and intensity of oceanic storms. These islands are being degraded at an alarming rate, in part because of anthropogenic attempts at stabilization. In this article, we outline a possible sustainability strategy that incorporates the natural degree of substrate instability on these sedimentary landscapes. We recommend placing the focus for managing barrier islands on maintaining ecosystem function and process development rather than emphasizing barrier islands as structural impediments to wave and storm energy.

ADDITIONAL INDEX WORDS: Barrier islands, coastal erosion, storm surge, sea level rise, coastal management, vegetation.

INTRODUCTION

Barrier islands are ecosystems that border coastal shorelines and physically separate the offshore oceanic province from inshore wetlands, bays, sounds, and estuaries. As their name implies, they form a protective barrier between continental shorelines and wave action that originates offshore. Barrier islands also provide the structural framework for the formation of an array of coastal and estuarine habitats that host a variety of native and migratory species, many of which have substantial economic value.

Coastlines fronted by barrier islands also include some of the greatest concentrations of human populations and accompanying anthropogenic development in the world (Schlacher et al., 2007; Weinstein et al., 2007). The native vegetation and geological stability of these ecosystems are coupled and vulnerable to erosion events, particularly when also disturbed by development. As a result, barrier islands are quite vulnerable to potential global warming impacts such as sea level rise (Intergovernmental Panel On Climate Change, 2007) and increase in the frequency and intensity of major oceanic storms (Emanuel, 2005; Webster et al., 2004). These islands are some of the most valuable yet potentially vulnerable ecosystems on Earth (Perez-Maqueo, Intralawan, and Martinez, 2007; U.S. Commission On Ocean Policy, 2004).

Our goal here is to outline a sustainability strategy that recognizes and incorporates the high degree of substrate instability found in these natural ecosystems. An ideal solution would involve a strategic compromise between anthropogenic development and preservation of the natural ecosystem.

NATURAL INSTABILITY

Barrier islands have an extremely dynamic nature whereby major changes in geomorphology and hydrology can occur over days, or even hours, in response to extreme episodic storm events (EESEs) such as tropical cyclones, hurricanes, and northeasters. Of most interest to the management community are changes that occur in response to these natural hazards. Barrier island width, dune elevation, tidal prism, wave energy, and storm surge energy influence the likelihood of overwash (Claudino-Sales, Wang, and Horwitz, 2008; Leatherman, Williams, and Fisher, 1977; Morton and Sallenger, 2003), transport of sediment offshore, and formation of new inlets during storms (Fitzgerald and Van Heteren, 1999). An array of endemic, indigenous, and migratory species are adapted specifically to such transient geological conditions (Brown and MacLachlan, 2002; Ehrenfeld, 1990; Shao, Shugart, and Hayden, 1996). However, little is known concerning the nature of the adaptive physiological mechanisms associated with this high level of transience, especially in response to EESEs, although these species are expected to have unique suites of evolutionary, genetic traits that underlie these adaptations (Gutschick and Bassirirad, 2003).

It is well documented that coastal plants are specifically adapted to take advantage of the dynamic nature of sediment transport in response to long-term processes, such as sea level rise or changes in sediment budget, having become adept "ecological engineers" (Costanza, Mitsch, and Day, 2006; Crain and Bertness, 2006; Halpern et al., 2007; Jones, Lawton, and Shachak, 1997). In classical works on both sand dunes (Cowles, 1899) and salt marshes (Redfield and Rubin, 1962), ecologists have shown that these plants capture sediment, elevate the substrate, and drive the successional process. For example, dunes are the result of sand accumulation, becoming larger as plant sizes, densities, and root depths increase (Tsoar, 2005) and mutualist interactions begin with …