FAIRHOPE, Ala. — Around 1,300 acres of seagrass have vanished from Baldwin and Mobile counties since 2002, according to a report recently prepared by Barry A. Vittor and Associates.

The survey, commissioned by the Mobile Bay National Estuary Program (MBNEP) and the Alabama Department of Conservation and Natural Resources State Lands Division (ADCNR-SLD), looks at 2008 and 2009 data gathered during an aerial survey of Mobile Bay, the Mobile-Tensaw Delta and the Mississippi Sound. The information was then compared with the results of a 2002 baseline study of seagrass coverage.

The report indicates the total acreage lost is primarily attributed to the areas measured in the delta and northern parts of the bay.

While the document suggests that Hurricane Ivan in 2004 and Katrina the following year might have played a role in the fluctuation — because of the possibility the two storms changed conditions such as water clarity and movement of sediments — it is not yet known how much of an impact they actually had, nor what other factors could have contributed to the decline as well.

“The reasons for SAV (submerged aquatic vegetation) decline in the Delta are not clearly known,” said Dr. Amy Hunter, MBNEP program scientist. ”In addition to natural storm events, physical factors such as light, temperature, salinity and wave energy control SAV distribution.

“Given the measured, consistent, loss of SAV in Mobile Bay, we have to consider the things that can impact those physical factors. For example, the amount of light reaching SAV is controlled by water clarity. Nutrient input, suspended sediment and stormwater runoff can all impact water clarity. It is then important and necessary to think about what human activity impacts those variables.”

Hunter said it is important to note that the southern portion of the study area had more SAV acreage mapped in 2009 and 2008, compared to 2002. There were 234.8 more acres of SAV mapped in 2009 overall in the Mississippi Sound and Perdido Key areas. Areas with greater acreage in 2009 compared to 2002 included the Orange Beach (+90.8 acres) and Perdido Bay (+20.8 acres) quadrangles in southern Baldwin County, and the Grand Bay (+67.8 acres), Petit Bois Pass (+82.7 acres), Isle aux Herbes (+41.6 acres) and Fort Morgan NW (+25.2 acres) quadrangles in southern Mobile County.

There were large changes in SAV acreage between the 2008 and 2009 surveys, with 438.8 fewer acres mapped in 2009. The difference between surveys was primarily due to less acreage of widgeon grass (Ruppia maritima) in Mississippi Sound in 2009, particularly in the Grand Bay and Isle aux Herbes quadrangles, according to the report summary.

The negative trend is concurrent with Vittor and Associates’ comparison of a 2002 seagrass survey with historical aerial photography, showing an 88 percent loss of seagrasses in Baldwin County and a 55 percent loss in Mobile County between the 1940s and 2002.

Hunter said, “In light of the approximately 79 percent loss of seagrass across the Mobile Bay study area over the last 60 years, these additional losses deserve our attention. Research coupled with innovative management techniques is key to understanding and reversing this negative trend.”

The report states that “SAV community distribution and composition are highly variable across multiple temporal scales, and are greatly affected by both interannual and seasonal variability in physical parameters (salinity, light and nutrient availability), and short-term environmental change. Identification of the primary factors contributing to temporal variability in SAV abundance and diversity in a dynamic system like the Delta likely would require detailed, species-specific assessments over several years.”

Hunter said, “Mobile Bay NEP funds mapping of SAV in the estuary every five years. We will continue to monitor the general trends. We hope that identification of the primary factors contributing to variability in SAV abundance and diversity in the delta will be studied in more detail.”

The 2009 report is the most recent accomplishment in a multi-year partnership between the MBNEP and ADCNR-SLD to monitor seagrass trends in coastal Alabama. Because of its sensitivity to changes in water quality, seagrass habitat is often considered an important indicator of coastal ecosystem health.

In the Mobile Bay estuary, seagrass loss can be attributed to natural subsidence and storm events, as well as human impacts such as stormwater runoff, sedimentation from commercial and residential development, and wastewater and other discharges.

To see the full report, visit www.mobilebaynep.com.