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January 24, 2006 Mobile, AL. Submerged aquatic vegetation (SAV) are under water plants that grow in relatively shallow waters along the coast. In a report prepared for the Mobile Bay National Estuary Program (Mobile Bay NEP), Barry Vittor and Associates reviewed historical SAV coverage in coastal Alabama and determined significant acreage loss in SAV has occurred since 1940. In 2002, the Mobile Bay NEP commissioned the first aerial photographic baseline study for current SAV coverage in Coastal Alabama. Barry Vittor and Associates was contracted to produce aerial true color digital orthophotoquads along the coast. Certain photographic signatures indicate various plant species. Once identified in aerials, scientists then “ground-truth” their results by physically checking the plants in the field. Maps of SAV coverage were then created. In a follow-up study, Barry Vittor and Associates then obtained historical aerial photosets of Mobile County from 1940 and Baldwin County from 1955 and 1966 to compare to the 2002 photosets. There is anecdotal information from long time residents and resource managers that SAV coverage was once far more widespread in the Mobile estuary. What Vittor’s group found was quite an impressive loss of submerged grasses. Between 1940 and 2002, areas in Mobile County decreased from 1924 acres to just 855 acres of SAV. Most of the loss was south of Dog River, 691 fewer acres along the western shore. Baldwin County analysis revealed a disturbing 88.3% loss between 1955 and 2002. The 1955 photoset revealed SAV from just north of Point Clear south to Bon Secour Bay. In 2002, no SAV were identified from that area. Between 1966 and 2002, the northeastern shore of Mobile Bay lost 328 acres or a 71% decrease. Why worry about SAV? Submerged grasses are like underwater meadows, providing critical “nursery” habitat and food for the young of many commercially and recreationally important species of fish, shrimp and crabs. They can also act as wave attenuators and help hold sediment in place in normal weather conditions. In addition, plants act like sponges for various pollutants thus acting as water and sediment filters. SAV were identified by Mobile Bay area stakeholders as issues of concern within the Mobile Bay NEP’s comprehensive plan. Changes in estuarine grass distribution can occur due to many natural coastal and climatic cycles. Much of the year to year variation observed by local residents, resource managers, and researchers is still being studied. However, the overall decline in this highly valuable habitat is largely due to human activity altering areas previously capable of supporting SAV. Increased rates of sedimentation or scouring, hardening shorelines, and other development practices can alter the setting in which submerged grasses grow. Once altered, the plants fail to thrive and the habitat can eventually die. Boating activities as well as recreational trawling can also tear up bay bottoms. The decline of SAV may also correlate to declines in other important aquatic species. Can submerged grasses be replanted like other plants? Unlike many other types of vegetation, SAV is very difficult to transplant successfully. Researchers and managers around the country work to understand the delicate balance these plants need in order to grow in controlled conditions and then thrive once transplanted to restoration sites. Many area organizations and agencies are working individually and through partnerships toward restoring SAV in coastal Alabama though success is yet to be achieved. Many of these groups work within the structure of the Mobile Bay NEP to address SAV loss and how it maybe restored. Final reports from both the 2002 baseline survey and 2005 historical SAV coverage are available in PDF file format on the Mobile Bay NEP website. Go to www.mobilebaynep.com and click on publications. *** For more
information contact: David Yeager 251-431-6409 |
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