Distribution and Status of Submerged Vegetation in Estuaries of the Upper Texas Coast

Adair, Stephen; Moore, Joseph; Onuf, Christopher

Abstract: Composition and biomasso f bedso f submergeda quatic vegetation( SAV) in estuariesa long the upper Texasc oastw ere examinedf rom bottom core and rake samplest aken along 72line transectsd uring July-August 1987.S ubstratec omposition,s alinity,w aterd epth,a nd waterc larity werea lsom easureda t each samples tation.H alodule wrightii was the dominant specieso f SAV meadows( 69% occurrence)f,o llowedb y Ruppia maritima (36Vo). Najas guadalupensis and, Vallisneria americana were only found in the shallow (<60 cm), oligohaline (<10 ppt) waters of Trinity Bay. Halophila engelmannii and Thalassia testudinumwere only found in the deeper (35-l l0 cm) euhaline waters (30-40 ppt) of Christmas and Matagorda Bays. H. wrtghtii and R. marilima occurreda crosst he greatesdt epth and salinity spectra,w ith R. maritima more prominent in shallower ( < 90 cm) mixohaline waters ( I G-30 ppt) and H . wrightii more prominent in euhaline waters (30-40 ppt). Beds of SAV were more extensive and had greater biomass along south shorelines compared to north shorelines (P < 0.045), and depth to which vegetation grew was positively correlated with waterc larity( r :0.927, P < 0.00l ). The correlationso f waterd epth,s alinity,a nd waterc larityw ithvariationi n SAV speciesc ompositiona nd distribution suggestth at abiotict olerancesd ocumentedb y previous experimental studies are major factors influencing field distributions. Comparisons with similar field data from the early 1970sc orroboratet he reportedd ecreasein SAV in the Galveston Bay complex and suggest a slight increasei n the MatagordaB ay complex. Declineo f SAV in the Galveston Bay complex coincided with major shorefront development and a decline in numbers of wintering redhead ducks Aythya americana.Proteclion of shorelineso f upper coast estuariesi s vital to maintaining SAV resourcesa nd the dependent fauna. Where possible,b arrier island preservess hould be establisheda djacentt o beds of SAV and development restrictions implemented to reduce impacts.

Distribution and Status of Submerged Vegetation in Estuaries of the Upper Texas Coast

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