PROGRESS IN BIOLOGICAL INQUIRIES, 1931 517 



Althoup:h starfish mops have been used for nioi-e than 50 years, 

 there seems to be no diminution in the number of starfish, and they 

 are as serious pests to-day as they were when control was first advo- 

 cated. A most wasteful result of mechanical control is the injury 

 to the 03'ster. Asitle from the fact that starfish are contimu)usly 

 eatinir oysters, the mops chains and dredjijes are continuously break- 

 ing otf the new shell growth faster than it can be deposited. Such a 

 practice continued over a ])eriod of time results in a stunted oyster 

 which requires another year of growth before marketing. 



Another phase of the problem is the actual number of shellfish 

 consumed by the starfish. Young starfish 2 or 3 days old can open 

 and digest a 3 or 4 day old spat in a little over 20 minutes. In 11 

 hours after an adult starfish crawled into a two-year-old oyster 

 it left the shell empty and absolutely clean. On July 21, 1931, 35 

 starfish, with an arm length between 4 and 7 centimeters were placed 

 in a wooden float in Cold Spring Harbor, and clusters of year-old 

 oysters provided as food. Twelve days later 46 oysters had been 

 eaten and after 30 days 79 were eaten and the average increase in 

 starfish arm length was 0.7 centimeter. Under population conditions 

 as they exist in some seriously infested areas, starfish could com- 

 pletely wipe out an oyster crop if left undisturbed. Because of the 

 inadequacy of the present mechanical methods of combating star- 

 fish, attempts were made to control them by chemical means. 



The chemistry of sea. w^ater is, however, so complicated, its living 

 organisms so varied and important to man, that it is indeed presump- 

 tions to propose the using of a poisonous chemical in the water as a 

 means of control. Studies have been made on cases of unusual 

 mortality of organisms or of their destruction due to pollution by in- 

 dustrial wastes, but little or no attempt has been made to artificially 

 change the sea water in order to limit certain forms. 



Such a procedure meets with seemingly and perhaps actually in- 

 surmountable difficulties. In the first place, any substance which 

 can kill one form is poisonous in a greater or less degree to nearly all 

 other living organisms. Their only hope of escape would be a more 

 effective protective mechanism. Starfish, having an exposed respira- 

 tory and circulatory system and a relatively slow locomotion, are less 

 able to protect themselves than oysters, crustacea, or fast-swimming 

 fish. 



Many chemicals were tried, but copper sulphate seemed to be the 

 only substance effective in small amounts and at the same time worthy 

 of practical consideration. During the summer of 1931, at the labo- 

 ratories of the Long Island Biological Association, experiments were 

 performed to determine the effect of that salt on starfish, oysters, and 

 other marine forms. 



Experiments with adult starfish show that the time necessary to 

 kill the organisms varies in relation to concentration from 2% hours 

 (10 parts of CuSOi per million) to 3 minutes (1,000 parts CUSO4 per 

 million). Starfishes of various age show remarkable difference in 

 susceptibility, the small individuals being affected in a shorter time 

 than the larger ones. For instance, starfish of less than 1 centimeter 

 will be killed by the concentration of 10 parts per million in 5 

 minutes, but those more than 5 centimeters long remain alive after 

 nearly 2 hours' exposure. 



