Molluscan distribution in Copano Bay, Texas

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Calnan, Thomas R.

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University of Texas at Austin. Bureau of Economic Geology


Benthic samples were collected on a 1-mi grid from Copano Bay, Texas, in March and April, 1976. Seventy-four molluscan species, including 33 pelecypods, 40 gastropods, and 1 scaphopod were taken from 93 stations in Copano Bay. Molluscan distribution was correlated with gross sediment, salinity, feeding type, and total organic carbon content. Seven sediment types were mapped in Copano Bay. The mud and sand end-members had fewer molluscan species and live individuals, whereas the muddy sands had the highest number of live individuals. Salinity averages from 1926 to 1976 have varied from less than 10 parts per thousand to 36 parts per thousand yearly. Salinities from 1971 to 1976 averaged less than 15 yearly. Fourteen of the 25 living molluscan species were euryhaline marine and could tolerate the highly variable salinities. Dead stenohaline marine species were common, but only one living stenohaline species was found. The two most abundant feeding types, the deposit and suspension feeders, numerically dominated in the muddy sands and muddy shells, respectively. Generally, stations with a high total organic carbon content also had a large population of deposit feeders, although there were some exceptions. Extensive Crassostrea virginica reefs are present in Copano Bay. Whole shells or fragments of oyster shell were found in 75 percent of the samples, and six stations had live Crassostrea. Odostomia impressa and Ischadium recurvum were the predominant mollusks at the reef stations.


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