Brackish Biomes of the Gulf of Mexico

Brackish biomesare easy to define in general terms: they are watery habitats that are less saline than the ocean and more saline than the freshwater biomes. But these habitats come in many forms or have many names such as marshes, wetlands, estuaries, mangrove swamps, inland seas and bogs.

Brackish biomes have a wide variety of life forms that are either freshwater forms that have adapted to more saline environments, or they are marine life forms that have adapted to less saline environments. Some fish, such as Salmon, are also capable of making annual migrations between the oceans and deep into freshwater zones in order to mate, grow and then spawn and die.

In the North and Eastern Gulf of Mexico, there is a world of unique brackish water environments. The State of Texas has barrier islands, estuaries with muddy bottoms, coastal wetlands, seagrasses, oyster reefs, salt marshes, and other man made and natural reefs. These habitats support five major life forms in the brackish water: alligators, whelks and three major species of crabs. In the estuaries and shallower waters, there are five species of turtle, Brown Pelicans and several species of flounder and other fish.

In much of Gulf Of Mexico brackish water, several species of sturgeon thrive. There are also livebearers, killfish, gobies and more that are popular in brackish home aquariums.

The Gulf has seagrass communities that have been known to rival tropical rain forests in their ability to serve as habitat for life and for production of plant material. It is estimated that a single acre of seagrass can produce tons of leaves annually, and can serve as habitat for about tens of thousands of fish and vertebrates.

Florida has the huge Suwanee River drainage basin that ends up in a small area of estuary and brackish water. There is also Tampa Bay, which holds many brackish water environments. Vast parts of Florida are mangrove swamps.

Alabama has the Mobile Bay watershed where freshwater ends in a small area that interfaces with the saline environment.

Louisiana has the Mississippi River and the Atchafalaya River that help to create  huge deltas for a major brackish environment that is unique in the world. Lake Pontchartrain is also brackish.

Finally, the Gulf of Mexico has the famous “dead zone” where annual runoff from the nutrient rich freshwater drainage basins causes stratification of the water, then prevents oxygen exchange. The brackish tidal marshes and seagrass lands are able to take in much of the nutrient load, but in Louisiana, have been deteriorating at alarming levels.

In summary, there is so much life in the brackish zones of the northern and northeastern Gulf of  Mexico that it can take a lifetime of study to identify it all, making this region one of the most important for understanding how brackish biomes work to provide support for life inland as well as on the open ocean.


Texas Aquatic Species

“Gulf Of Mexico Seagrass”, USGS Publication 4

“Seagrass Facts”, Garden Guides