PROGRESS IN BIOLOGICAL INQUIRIES, 1933 357 



the recent oyster mortality in Terrebonne Parish and its possible 

 relation to oil-well ])ollution of those waters. Oyster planters oper- 

 atino; in the vicinity of the oil wells in Lake Pelto and Lake Barre 

 suli'ered a heavy loss of their stock durinj^ the winter of 11132-33 and 

 to a lesser degree during the previous winter. 



A preliminary survey of this region by Dr. Prytherch in May 1933 

 showed that 50 to 95 percent of the adult oysters on the planted beds, 

 had died previously but no direct relation could be established be- 

 tween the degree of mortality on these areas and their distance from 

 the oil wells. Pollution of the water by oil, brine effluent, and gas 

 (HnS) was greatest in the vicinity of the Lake Barre wells, and yet 

 live oysters were found on the piling of these wells and on a natural 

 bed in their immediate vicinit3^ 



The problem is further complicated by the fact that the mortality 

 was limited chiefly to the larger oysters and that the natural enemies, 

 the boring sponge and boring clam, wdiich hexivily infested most of 

 their shells, were apparently unaffected under the same conditions. 

 A severe attack of these enemies lowers the vitality of the oyster and 

 it is believed that such a condition was an important contributing 

 factor in the mortality of many of these oysters. 



On several beds, however, a high death rate occurred Avhere there 

 was no evidence of the boring sponge or clam. Fortunately it was 

 possible to obtain samples of weak surviving oysters from these areas 

 and others for miscroscopical studies, which have subsequently shown 

 that the tissues of the muscle and gills were heavily infected with a 

 minute protozoan parasite. Studies are being continued of the life 

 history and occurrence of this protozoan parasite in Louisiana oysters 

 and its possible relation to recent mortality. 



EXeERIMEXTAL STUDIES OF OIL-WELL POLLUTION 



Since pollution of the waters of Terrebonne Parish was coincident 

 with the oyster mortality, it was necessary that laboratory experiments 

 be conducted to determine whether tlie different polluting substances, 

 crude petroleum, brine water and hydrogen sulphide, are toxic to 

 oysters and other marine animals and in what concentration. At the 

 Beaufort Laboratory this work has been in progress since July and 

 has shown that (1) oysters, clams, and numerous marine inverte- 

 brates will survive and grow in water covered with a heavy film of 

 crude petroleum; (2) shellfish are not killed when fed on suspensions 

 of these oils and show no cessation in gro\^i;h of shell; (3) oystei-s 

 survive when completely inmiersed in oil once each hour over a period 

 of 6 weeks; and (4) 03'sters and clams will grow on mud and sand 

 bottoms saturated wath different grades of oil. These experiments 

 are being continued. 



The most serious pollution from the oil wells is apparently the 

 brine water extracted from the petroleum. The effect of the different 

 brines on feeding, growth, and shell movements of the oyster are 

 being investigated. Though small amounts have been found to be 

 nontoxic to larval, spat and adult oysters over a short period of 

 time, general conclusions cannot be drawn until the effects over a 

 prolonged period have been determined. Dilute solutions of brine 

 of the same salinity, pH, and oxygen content as sea water were 

 found to be toxic to oysters and produced death in from 6 to 10 days. 



