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A survey of submerged aquatic vegetation in estuaries along the northern Gulf of Mexico coast.
Carter, Jacoby*,1, Arrivillaga, Alex2, Merino, Sergio2, 1 USGS National Wetlands Research Center, Lafayette, LA, 705062 Johnson Controls Worldwide Services, LA, 70506, USA
ABSTRACT- The distribution of estuarine submerged aquatic vegetation (SAV) along the Gulf of Mexico coast is not as well known as it is for fresh and marine species. Also there have been accounts that the exotic macro algae Caulerpa taxifolia has been invading estuarine systems on both the US Atlantic and Pacific coasts. In June and July 2001 and 2002 we conducted a survey of SAV in coastal estuaries along the Gulf of Mexico coast from Anclote Key, Florida to Laguna Madre, Texas. Estuaries visited were selected based on USGS hydrologic units in a stratified random fashion to provide for even sampling across the coast. We would then move up or down the salinity gradient of the estuary looking for beds of SAV within 5 different salinity zones: 0-5 ppt, 6-10 ppt, 11-15 ppt, 16-20 ppt, and 21+ ppt. When we located SAV beds we recorded their location with a GPS; species composition, water quality data (pH, salinity, temperature, etc.); collected water quality samples for later nutrient and chlorophyll analysis; and sediment samples for later characterization. We also noted boat traffic and amount of nearby development. We sampled 276 SAV beds in Florida, Alabama, Mississippi, Louisiana and Texas. Thirteen non-algal aquatic macrophytes occurred 2 or more times in our samples. The 4 most frequently occurring species (20+ times) were widgeon grass (Ruppia maritima, n=148), an aquatic spike rush Eleocharis parvula? (n=47), shoal grass (Halodule wrightii, n=36) and the exotic invasive Eurasian water-milfoil Myriophylum spicatum (n=31). The mean salinity for SAV considered seagrasses were all above 15 ppt. The mean salinity of Ruppia was 9 ppt, and with the exception of the aquatic spike rush the rest of the salinity means were at or below 5 ppt. Water clarity and salinity were the two most important factors affecting distribution. The results from this survey indicate that at least for SAV along the Gulf of Mexico Coast, the problem of exotic species invasions seems to be restricted to fresh water systems.
Key words: survey, submerged aquatic vegetation, Gulf of Mexico, estuary