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Ivan Causes Habitat Changes in Mobile Delta

November 01, 2004

Hurricane Ivan recently struck the Gulf Coast of Alabama with its unrelenting fury. Video of destruction to homes and businesses is prevalent, but information about how this storm impacted Alabama’s aquatic plant life in the Mobile Delta is not as well publicized.

According to Joe Jernigan, fisheries biologist with the Division of Wildlife and Freshwater Fisheries, plant communities are constantly changing, so documenting the effects of a hurricane can be difficult. In 1979, an aquatic plant survey was conducted just prior to Hurricane Frederic. “From a biologist’s viewpoint, the timing could not have been better, because a post hurricane follow-up survey was conducted to determine the changes that took place,” said Jernigan. The destruction was widespread. Surveys prior to the storm found that approximately 50 percent of McReynolds Lake and the surrounding creeks were covered in Brazilian elodea, a submerged aquatic plant with a low tolerance for salinity. Following the storm, plants in the area were difficult to find.

To this day, the Brazilian elodea has not recovered and has now been replaced by hydrilla. Immediately following Frederic, emergent plant beds throughout the Delta appeared to have been destroyed. But, one year later, the emergent plant communities were thick and lush, and little evidence of the ill effects of the hurricane remained.

What does all this mean for the aquatic plant communities in the Mobile Delta this year? Jernigan says the surge of water from a storm like Frederic or Ivan can cause large amounts of salt water to be pushed into the Lower Delta and the surrounding emergent marsh. “The tremendous wave action can produce a physical pounding on many plant beds, especially south of the causeway. The combination of these two environmental forces will change the vast plant beds in the Lower Delta for some time. Plants that are euryhaline, or more salt tolerant, will survive better than plants with lower salt tolerances,” he said. Plant beds in more protected areas above the causeway will not suffer as devastating an effect from waves as plants located along more exposed shorelines.

In the short term, many plant communities in the Mobile Delta will be lost – either destroyed by waves or killed by high salinity. However, the Delta is a strong dynamic system capable of recovering from large natural events. Although some plant communities will recover more quickly than others, the ecosystem as a whole will remain healthy.

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