Protecting Marine Habitats

Protecting Marine Habitats

Estuarine and Marine Waters

Estuarine reserve
Texas Mission-Aransas National Estuarine Research Reserve. Photo credit: NOAA.

The Gulf coast area comprises more than 750 estuaries (areas where freshwater and saltwater mix), bays and sub-estuary systems associated with larger estuaries. The condition of coastal waters of the Gulf Coast region, according to the U.S. Environmental Protection Agency’s 2012 National Coastal Condition Report IV, is rated fair, with 10% of all coastal waters rated poor and 53% rated fair.

Hypoxia, or low oxygen conditions, occurs in some areas of the Gulf. For example, Mobile Bay has experienced regular hypoxic events since colonial times. Although hypoxia in many areas of the Gulf is a relatively local occurrence, the second largest area of oxygen depleted waters in the world, known as the Gulf Dead Zone, forms off the coast of Louisiana each year.  

GRN works in Gulf states to reduce the discharge of pollution into the Gulf, as well as pollution discharged into waters that flow into the Gulf. 


Turtle grass
Turtle grass. Photo credit: FDEP.

Seagrasses are submerged flowering plants growing in bays, lagoons, and shallow coastal waters. Seagrass beds are highly productive marine plant communities that: (a) provide valuable habitat including nursery habitat for fish, shrimp, sea turtles and manatees and forage for wintering waterfowl,(b) remove nutrients and other pollutants from coastal runoff; (c) providing, as well as forage for wintering waterfowl; and (d) stabilizing coastal sediments, decrease wave energy.  

Unfortunately, the distribution and abundance of Gulf’s seagrasses have declined during the past 50 years. The major threats to seagrasses are:

  1. Meteorological events, such as storms or hurricanes, can increase wind and wave action, causing increased turbidity and erosion that damage seagrass beds. Seagrass beds usually rebound from the effects of these natural events.
  2. Human induced impacts, which can have severe and long-lasting negative effects on seagrass beds, including:
    • any action that decrease water quality in the marine environment effecting photosynthesis 
    • nutrient pollution from human development in coastal areas which can cause macroalgae to “overgrow” seagrass; and phytoplankton blooms that reduce water clarity; and 
    • direct damage to seagrass beds, such as scarring from boat propellers or trawl nets that can have cumulative impacts on the ecosystem.

GRN works with groups throughout the Gulf to reduce pollution and improve the water quality needed to support healthy seagrasses. 


Lobed Star Coral
Lobed star coral. Photo credit: Flower Garden Banks/NOAA.

Corals are marine animals related to jellyfish and anemones. Coral reefs are formed by corals that secrete hard calcareous exoskeletons, giving them structural rigidity. Corals, the largest living structures on earth, develop when “hard corals” form elaborate finger-shaped, branching or mound shaped structures that can create masses of limestone (reefs) that stretch for tens or even hundreds of miles. The world’s third largest barrier reef is found of the waters of Florida, in the Florida Key’s National Marine Sanctuary.

The Gulf is also home to coral communities that occur in the deeper waters of the Gulf of Mexico, including Pulley Ridge, the Pinnacles, the South Texas Banks, West Florida Slope Lithoherms, the East and West Flower Banks, Horseshoe Bank and Viosca Knolls.

Primary Threats to Corals

Disease: Corals face serious risks from various diseases, including black-band, white-band, and yellow-band diseases. The susceptibility of corals to disease may be on the rise as a result of human activities. 

Ocean Acidification: Rising levels of atmospheric carbon dioxide also mean that the amount of carbon dioxide being absorbed by the oceans is increasing. As carbon dioxide levels go up, seawater becomes more acidic. This chemical reaction reduces the number of carbonate ions in seawater available for corals and other marine organisms to build their calcium carbonate skeletons and damages or kill corals.

Bleaching: In response to stressful conditions, corals can expel an algae, called zooxanthellae, that is critical to their health. This is the process known as coral bleaching, and can result in corals’ deaths. One known cause of coral bleaching is increases in ocean temperatures. As ocean temperatures warm due to climate change, incidences of coral bleaching may increase.  

Pollution: Oil spills and pollutants can threaten entire reefs. For example, the BP oil disaster resulted in the release of thousands of barrels of oil and 1.84 million gallons of dispersant. Scientists studying the impact of the BP disaster have found that coral communities within 7 miles of the spill site have suffered serious injury.
Excessive nitrogen and phosphorous pollution from land sources, such as fertilizer runoff and untreated sewage, also harm corals by promoting the growth of algae that can smother corals. 

Overfishing: Under normal conditions, herbivorous fish and some invertebrates keep algae populations in corals balanced. However when those fish are overharvested algae growth goes unchecked, smothering corals. Other organisms harmful to corals, such as crown-of-thorns starfish, also multiply when the species that prey on them are removed.