Distribution and status of submerged vegetation in estuaries of the upper texas coast

Abstract

Composition and biomass of beds of submerged aquatic vegetation (SAV) in estuaries along the upper Texas coast were examined from bottom core and rake samples taken along 72 line transects during July–August 1987. Substrate composition, salinity, water depth, and water clarity were also measured at each sample station.Halodule wrightii was the dominant species of SAV meadows (69% occurrence), followed byRuppia maritima (36%).Najas guadalupensis andVallisneria americana were only found in the shallow (<60 cm), oligohaline (<10 ppt) waters of Trinity Bay.Halophila engelmannii andThalassia testudinum were only found in the deeper (35–110 cm) euhaline waters (30–40 ppt) of Christmas and Matagorda Bays.H. wrightii andR. maritima occurred across the greatest depth and salinity spectra, withR. maritima more prominent in shallower (<90 cm) mixohaline waters (10–30 ppt) andH. 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 water clarity (r=0.927, P<0.001). The correlations of water depth, salinity, and water clarity with variation in SAV species composition and distribution suggest that abiotic tolerances documented by previous experimental studies are major factors influencing field distributions. Comparisons with similar field data from the early 1970s corroborate the reported decrease in SAV in the Galveston Bay complex and suggest a slight increase in the Matagorda Bay complex. Decline of SAV in the Galveston Bay complex coincided with major shorefront development and a decline in numbers of wintering redhead ducksAythya americana. Protection of shorelines of upper coast estuaries is vital to maintaining SAV resources and the dependent fauna. Where possible, barrier island preserves should be established adjacent to beds of-SAV and development restrictions implemented to reduce impacts.