BIOTIC CHANGES IN A BAY ASSOCIATED WITH THE END OF A DROUGHT1

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Abstract
Heavy rainfall in early 1957 broke the most severe drought in the history of Texas. Resultant heavy river discharge reduced salinities in Mesquite Bay on the Central Texas Coast by over 30‰ in two months. Effects on the bay fauna were catastrophic with complete mortality of stenohaline marine sessile and infaunal mollusks. The flora and fauna of the high salinity drought period and of the subsequent low salinity period are compared. A high salinity Ostrea equestris‐Brachidontes exustus community was replaced in 1957 by a Crassostrea virginica‐Brachidontes recurvus community. The rapid lowering of salinity apparently did not kill fishes and other motile forms; in most cases these must have escaped by moving out of the area, but several stenohaline species were found in very low salinities immediately after the influx of fresh water. Mortality of euryhaline mollusks occurred in 1958 when salinities fell below 3‰. Some relations of organisms to salinity are discussed from ecological and paleoecological viewpoints.