The encroachment of black mangroves, Avicennia germinans, into salt marshes has great potential to change the coastal landscape, affect ecological processes, and alter key habitat for a variety of species. Many studies have focused on Avicennia-Spartina alterniflora interactions; however, climate models show that rising temperatures and changing precipitation patterns may lead to prolonged hypersaline conditions. Under harsher temperature and salinity stress, saltmarsh composition may shift from Spartina to a variety of succulents, such as Batis and Salicornia, or tidal flats which may change the nature of marsh-mangrove interactions in unknown ways. In the Gulf of Mexico, Avicennia has colonized novel habitats with varying physical and biological factors. Understanding how interactions with various marsh species and multiple stresses affect seedling growth can provide more insight into what salt marsh habitats may be vulnerable to encroachment and how Avicennia may adapt to novel conditions. The ability of Avicennia to respond to changing conditions can be attributed to local adaptations, phenotypic plasticity and maternal contribution. The relative importance and interactions of these factors can affect species interactions and population dynamics.
Results/Conclusions
My study is a reciprocal transplant experiment investigating Avicennia seedling survival and growth rates under normal saline and hypersaline conditions in various marsh habitats to determine the effects of vegetation and salinity interactions and maternal contribution. Propagules were collected from Southern Laguna Madre and Oso Bay, Texas to represent hypersaline and normal saline conditions, then planted in Oso Bay and the Laguna Madre Field Station. Once planted, seedlings were checked weekly to assess root establishment, quality of cotyledons, development of leaves and overall height. After a few weeks, majority of seedlings planted in tidal flats suffered high mortality at both sites. The first development of leaves was observed four weeks after planting at the Laguna Madre station in a seedling from Oso Bay under Avicennia canopy cover. At 5 weeks’ time, a seedling from Southern Laguna Madre had developed leaves at the Laguna Madre site also under Avicennia canopy cover. Thus far, no seedlings at the Oso Bay site have developed leaves. Although data are premature, trends could indicate that Avicennia seedlings develop better in shaded conditions and that hypersalinity may reduce competition with surrounding vegetation.