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Mid-Coast Barrier Islands and Coastal Marshes

Ecoregion in Atlantic Coastal Plain, TX

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The Mid-Coast Barrier Islands and Coastal Marshes portion of the Texas coast is subhumid compared to the humid climate of Ecoregion 34g to the northeast and to the semiarid climate of Ecoregion 34i to the south. Annual precipitation within Ecoregion 34h increases to the northeast, ranging from 34 to 46 inches. The region encompasses primarily Holocene deposits with saline, brackish, and freshwater marshes, barrier islands with minor washover fans, and tidal flat sands and clays. In the inland section from Matagorda Bay to Corpus Christi Bay, Pleistocene barrier island deposits occur. Typical soils on the coastal marshes are Entisols, with a minor extent of Histosols. Mollisols occur on tidal flats and coastal marshes, and Entisols form in sandy barrier islands and dunes. Smooth cordgrass, marshhay cordgrass, and gulf saltgrass dominate in more saline zones. Other native vegetation is mainly grassland composed of seacoast bluestem, sea-oats, common reed, gulfdune paspalum, and soilbind morning-glory. Some areas have clumps of sweetbay, redbay, and dwarf southern live oak trees. In the Coastal Bend area, the barrier islands support extensive foredunes and back-island dune fields. Scarps can characterize bay margins due to beach erosion. Salt marsh and wind-tidal flats are mostly confined to the back side of the barrier islands with fresh or brackish marshes associated with river-mouth delta areas. Marshhay cordgrass becomes less important to the south in this region. Black mangrove begins to appear from Port O’Connor south. This area of the coast has all three commercially important species of shrimp as well as important oyster and blue crab fisheries. Convergence of longshore currents from north and south occurs south of the Corpus Christi area near Padre Island National Seashore. Corpus Christi Bay serves as the ecozone or boundary between two distinct estuarine ecosystems. Copano and Mesquite bays to the north are low to moderate-salinity bays and attract whooping cranes and other birdlife. To the south in 34i, hypersaline Laguna Madre forms a unique ecosystem and supports greater expanses of seagrasses.

— EPA

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