Scientific contributions of the Mangrove Macrobenthos and Management (MMM) conference series, 2000–2019

10.1016/j.ecss.2020.106742Estuarine, Coastal and Shelf Science248106742-10674

Jump‐starting coastal wetland restoration: a comparison of marsh and mangrove foundation species

During coastal wetland restoration, foundation plant species are critical in creating habitat, modulating ecosystem functions, and supporting ecological communities. Following initial hydrologic restoration, foundation plant species can help stabilize sediments and jump-start ecosystem development. Different foundation species, however, have different traits and environmental tolerances. To understand how these traits and tolerances impact restoration trajectories, there is a need for comparative studies among foundation species. In subtropical and tropical climates, coastal wetland restoration practitioners can sometimes choose between salt marsh and/or mangrove foundation species. Here, we compared the early life history traits and environmental tolerances of two foundation species: (1) a salt marsh grass (Spartina alterniflora) and (2) a mangrove tree (Avicennia germinans). In an 18-month study of a recently restored coastal wetland in southeastern Louisiana (USA), we examined growth and survival along an elevation gradient and compared expansion and recruitment rates. We found that the rapid growth, expansion, and recruitment rates of the salt marsh grass make it a better species for quickly establishing ecological structure at suitable elevations. The slower growth, limited expansion, and lower recruitment of the mangrove species show its restricted capacity for immediate structural restoration, especially in areas where it co-occurs with perennial salt marsh species. Our findings suggest that the structural attributes needed in recently restored areas can be achieved sooner using fast-growing foundation species. Following salt marsh grass establishment, mangroves can then be used to further assist ecosystem development. This work highlights how appropriate foundation species can help jump-start ecosystem development to meet restoration objectives

Macroclimatic change expected to transform coastal wetland ecosystems this century

Coastal wetlands, existing at the interface between land and sea, are highly vulnerable to climate change1,2,3. Macroclimate (for example, temperature and precipitation regimes) greatly influences coastal wetland ecosystem structure and function4,5. However, research on climate change impacts in coastal wetlands has concentrated primarily on sea-level rise and largely ignored macroclimatic drivers, despite their power to transform plant community structure6,7,8,9,10,11,12 and modify ecosystem goods and services5,13. Here, we model wetland plant community structure based on macroclimate using field data collected across broad temperature and precipitation gradients along the northern Gulf of Mexico coast. Our analyses quantify strongly nonlinear temperature thresholds regulating the potential for marsh-to-mangrove conversion. We also identify precipitation thresholds for dominance by various functional groups, including succulent plants and unvegetated mudflats. Macroclimate-driven shifts in foundation plant species abundance will have large effects on certain ecosystem goods and services5,14,15,16. Based on current and projected climatic conditions, we project that transformative ecological changes are probable throughout the region this century, even under conservative climate scenarios. Coastal wetland ecosystems are functionally similar worldwide, so changes in this region are indicative of potential future changes in climatically similar regions globally