Effects of Black Mangrove (Avicennia germinans) Expansion on Saltmarsh (Spartina alterniflora) Benthic Communities of the South Texas Coast

Abstract

Black mangroves are becoming more common in several areas along the Texas coast and encroaching on existing saltmarsh habitats (Everitt et al. 2007, 2008, 2010). Expansion has been documented through the use of aerial photography on South Padre Island (Everitt et al. 2007, 2008, 2010), through Texas General Land Office land surveys in the Matagorda and San Antonio Bays area (White et al. 2002), and anecdotally in the Corpus Christi and Port Aransas areas. Both black mangrove (Avicennia germinans) and saltmarsh, composed primarily of smooth cordgrass (Spartina altemiflora), are productive estuarine habitats that support a diverse group of benthic organisms. They serve as nursery ground for many species of fish and invertebrates and provide a source of organic nutrients (Chen and Twil-ley 1999, Stevens et al. 2006). Avicennia germinans and S. altemiflora are found in similar estuarine locations and can be found in close association (Britton and Morton 1989, Kangas and Lugo 1990). The distribution of these species is largely dependent on climate and salinity (Penfound and Hathaway 1938, Sherrod and McMillan 1985, Kangas and Lugo 1990, Saenger 2002). However, environmental factors such as freshwater inflow, salinity, and nutrient levels can favor the expansion of black mangrove into Spartina habitats from which S. alterniflora do not often recolonize (Eady 2007).