618 U. S. BUREAU OF FISHERIES 



differences between the two samples. The Petrological Laboratory 

 of the Geological Survey examined them and found that the part 

 designated as clay was composed mainly of diatoms, which were 

 evenly distributed in both samples. 



A further study is planned on the consistency of bottoms and the 

 degree of hardness necessary for the planting of oysters. 



CONTROL or STARFISH ON OYSTER BEDS 



A study of the biology of the starfish with the view of finding 

 a practical method of eliminating from oyster beds this animal, 

 which is so destructive to oysters, was made by Louise Palmer at 

 Cold Springs Laboratory, Long Island. Oyster growers in Long 

 Island Sound spend thousands of dollars each year in fighting this 

 serious pest, for starfish devour countless numbers of oysters through- 

 out their whole life history from the time the larvae set on the shell's 

 until the mature oyster is marketed. Young starfish no larger than 

 a pinhead eat many of the newly set oysters, termed spat, during a 

 24-hour period, while large starfish take several hours to open and 

 consume the adult oyster, 2 or 3 years old. One grower in Long 

 Island Sound kept accurate records of the amount of starfish caught 

 on his beds in one year. In 1929, he removed 650 tons from Nara- 

 gansett Bay. This not only meant a loss of hundreds of dollars in an 

 effort to destroy these pests but an incalculable loss due to the number 

 of oysters already destroyed. 



In 1889 Doctor Meade, now of Brown University, working for the 

 U. S. Bureau of Fisheries, studied the habits of the starfish in order 

 to discover some angle of attack for extermination. Since that time 

 no effort has been made to learn the natural history of starfish in 

 different regions or to study their ecology and physiology with the 

 purpose of control. 



Since mechanical control of starfish as now practiced is expensive, 

 time consuming, and effective only in limited areas, an attempt was 

 made during the summers of 1929 and 1930 to find some chemical 

 means which would be effective and practical on the beds for their 

 eradication. Many chemicals were tried, but copper sulphate was the 

 only substance found to be effective in minute amounts and at the 

 same time worth practical consideration. During the past summer 

 tests were made to determine the effectiveness of this salt on the star- 

 fish, the oyster, and other marine forms. 



Large starfish were more resistant to copper sulphate than small 

 ones. Starfish of all sizes were killed by exposure of 12 to 15 minutes 

 to concentrations of 100 parts of copper sulphate to 1,000,000 parts 

 of water, the larger ones requiring the longer exposure and so on 

 until the smallest tested were killed with 4 minutes' exposure. The 

 time of exposure is inversely proportional to the concentration, 15 

 seconds' exposure being sufficient for death in concentrations of 

 1,000 parts per million. The minute starfish are killed by concen- 

 trations of 10 parts per million but this concentration is ineffective 

 for large starfish except for impractically long exposures. 



The effect of the copper sulphate is dependent on salinity, hydro- 

 gen-ion concentration, and temperature. A chemical reaction occurs 

 between the copper from the sulphate and the carbonate in the sea 



