Distribution of Marine Grasses in Southern Laguna Madre

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Date

1977

Authors

Chin, John L.

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Abstract

The study area of this report encompasses approximately 80 square miles of lagoon bottom off the Arroyo Colorado River in Southern Laguna Madre, Texas. The climate is semi-arid, as evaporation exceeds precipitation each year. Average monthly rainfall shows a bimodal distribution. Fresh-water runoff from the mainland into the lagoon is essentially negligible. Prevailing winds are from the southeast. The majority of geologic and hydrologic work is done by southeast and south-southeast winds. The daily effect of the tide decreases away from Brazos Santiago Pass. Furthermore, wind tides are the primary force controlling water circulation and inundation of lowlands in the Lower Laguna Madre.

Fieldwork was conducted from March through April. Three hundred and eight bay-bottom samples were taken on a one-half mile grid. Field identifications and observations served as the basis for 1977 maps of seagrass distribution and density. Available mapping, from the Texas Parks and Wildlife Department, documented seagrass distribution and density for the years 1961, 1965, 1966, and 1969 to 1973.

Five marine spermatophytes occur on the Texas Gulf Coast: Halodule wrightii, Ruppia maritima, Syringodium filiforme, Halophila engelmannii, and Thalassia testudinum. All but Thalassia were encountered in the study area.

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