Decline of Submerged Vegetation in the Galveston Bay System: Chronology and Relationships to Physical Processes

Abstract

Changes in submerged vascular plant distribution since the 1950's were documented for the Galveston Bay system (excluding the Trinity River delta proper) using aerial photographs and substantiated field reports. Two major regions where seagrasses have declined extensively were compared with nearby sites where vegetation persists. Along the upper bay shoreline, evidence is presented for involvement of Hurricane Carla (1961) and a relative rise in sea level due to subsidence, which resulted in the disappearance of Ruppia maritima beds between 1960 and 1962. In the lower bay (West Bay), mixed beds of R. maritima and Halodule wrightii declined steadily from the 1950's and disappeared by the early 1980's. This area contrasts with Christmas Bay, a secondary protected bay 5 to 7 km south that still contains extensive beds of H. wrightii and small patches of Thalassia testudinum and Halophila engelmanni, In West Bay, urban development, wastewater discharges, chemical spills, and dredging activities, rather than subsidence and Hurricane Carla, are suspected as the principal deleterious agents. Similarities between submerged vegetation declines in Galveston and other bay systems are discussed.