COMPARATIVE DISTRIBUTION OF MOLLUSKS IN DREDGED AND UN- 

 DREDGED PORTIONS OF AN ESTUARY, WITH A SYSTEMATIC LIST 

 OF SPECIES > 



BY JAMES E. SYKES AND JOHN R. HALL, FISHERY BIOLOGISTS 



BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY 



ST. PETERSBURG BEACH, FLA. 33706 



ABSTRACT 



A survey of benthic mollusks In Boca Clega Bay, Fla., 

 showed a much smaller number and variety of species 

 in the soft sediments in dredged canals than in the 

 predominantly sand and shell sediments in undredged 



areas. Samples contained an average of 60.5 live mollusks 

 and 3.8 species in undredged areas and I.l individuals 

 and 0.6 species in dredged canals. A list of mollusks 

 collected in this survey and in past studies Is appended. 



This report compares the numbers and vari- 

 eties of mollusks in fine sediments of dredged 

 canals with those found in undisturbed bottoms 

 of sand and shell in Boca Ciega Bay, Fla. The 

 bay is a shallow coastal lagoon of about 70 km.* 

 which connects with Tampa Bay at its southern 

 end (fig. 1). Some of the previous investigations 

 in the lagoon included studies of sediments 

 (Goodell and Gorsline, 1961; Taylor and Saloman, 

 1969); hydrology (Saloman and Taylor, 1968); 

 submerged vegetation (Pomeroy, 1960; Phillips, 

 1960) ; fishes (Springer and Woodburn, 1960; Sykes 

 and Finucane, 1964) ; and benthic invertebrates 

 (Hutton, Eldred, Woodburn, and Ingle, 1956; 

 Bullock and Boss *). 



A recent evaluation of the effects of dredging 

 and filling has documented a large loss of estu- 

 arine resources in Boca Ciega Bay (Taylor and 

 Saloman, 1968). It was here that scientists and 

 conservationists were finally successful in sup- 

 pressing a dredge-fill proposal of 202 ha. (Sykes, 

 1967). Tliis is also the bay in which the U.S. 

 Army Corps of Engineers denied a dredge-fill 

 application for the first time on the basis of 

 fish and wildlife values, thus providing a stim- 

 ulus for more comprehensive assessments of the 



' Contribution No. 57, Bureau oJ Commercial Fisheries Biological Labora- 

 tory, St. Petersburg Beach, Fla. 33706. 



> Bullock, R., and C. Boss. 1963. Ecological distribution oJ marine mol- 

 lusks In Boca Ciega Bay, Florida. Winter term project. Mimeographed 

 report on file at Florida Presbyterian College, St. Petersburg, Fla. 33733. 



biological and recreational aspects involved in 

 future bayfill developments. 



Thorson (1956) and others have concluded 

 that sediment composition is a cardinal factor 

 in controlling the settlement and viability of 

 many marine invertebrates. The distribution 

 of sessile benthic mollusks indicates to the marine 

 ecologist the ability of the environment to sup- 

 port life. Marked deficiencies in abundance and 

 variety indicate abnormality of the environment, 

 and the degi-ee of deficiency is roughly propor- 

 tional to the degree of abnormahty. 



PROCEDURES 



Between September 1963 and August 1964, we 

 took 107 bottom samples at 31 stations in Boca 

 Ciega Bay (figs. 1 and 2). Seven stations were 

 in canals between finger fills (1-7), and the other 

 24 (8-31) were m relatively undisturbed areas 

 of the bay. We collected algae, sea grasses, and 

 benthic animals with a bucket dredge and bot- 

 tom drag (Taylor, 1965). In water less than 

 1 m. deep, three shovelfuls of bay bottom (about 

 15 1.) were substituted for the dredge haul. One 

 station sample consisted of the combined catch 

 from one bucket dredge (or three shovelfuls) 

 and one bottom drag. At each station a sub- 

 sample of sediment was taken from the dredge 

 or shovel and was later analyzed at Florida 

 State University. 



Published May 1970. 



FISHERY BULLETIN: VOL. 68, NO. 2 



299 



