Sea stars need only to open valves slightly to begin digestion. To test 

 whether opening is possible solely by force a small notch was filed in the 

 mid-ventral edges of several clams and the hook of a spring balance was 

 inserted. A force of 7 to 10 lbs (3,000 to 4,500 g) was sufficient to 

 cause a gape of 2 mm. Adductor muscles were then severed and rubber bands 

 strong enough to withstand a greater force were wrapped around the valves. 

 Sea stars were able to overcome the resistance of the strong rubber. After 

 5 min valves were open about 2 mm and remained open for 3 min then snapped 

 closed, presumably on the everted stomach of the sea star. Soon the valves 

 were opened again for about 5 min. This process of opening and closing 

 continued for about 1/2 hr, then the sea star gave up. This proves that a 

 sea star can open a clam by force alone, and that a toxic substance is not 

 necessary. When valves are open 1 mm or less, enzymes of the sea star 

 stomach digest the living clam, causing adductor muscles to fail after a 

 relatively short time. Apparently the stomach of the sea star is not 

 necessarily damaged if the clam closes while this process is going on. - J.L.M. 



214 



Burrell, Victor G. , Jr. 1977. 



Mortalities of oysters and hard clams associated with heavy runoff in the 

 Santee River system, South Carolina in the spring of 1975. Proc. Natl. 

 Shellf. Assn. 67: 35-43. 



Although Mercenaria me r a en aria normally does not tolerate salinities below 

 10 to 13°/°°, conditions under which oysters can survive, hard clams 

 survived two periods of low salinity with less than 5% mortality, whereas 

 32% to 66% of oysters died. Changes in ionic concentration were measured 

 by conductivity determinations on shell cavity liquor. At lowest salinities, 

 conductivity of clam liquor was considerably higher than ambient salinity. 

 Oysters showed a greater range of conductivity, but also maintained higher 

 conductivity than surrounding water during heavy runoff. Low concentrations 

 of dissolved O2 and presence of H2S, associated in some places with high 

 runoff, did not appear to be implicated. Lower clam mortality probably was 

 related to their ability to remain closed longer than oysters. - J.L.M. 



215 



Burson, S. L., Jr., M. J. Fahrenbach, L. H. Frommhagen, B. A. Riccardi, R. A. 

 Brown, J. A. Brockman, H. V. Lewry, and E. L. R. Stockstad. 1956. 



Isolation and purification of mactins, heparin-like anticoagulants from 

 Mollusca. J. Am. Chem. Soc . 78(22): 5874-5878. 



Experimental animals were surf clam and ocean quahog. Mercenaria mercenaria 

 is not mentioned. - J.L.M. 



216 



Butler, Philip A. 1951. 



Experimental planting of hard clam, Venus. U.S. Fish Wildl . Serv. , Br. 

 Fish. Biol., Ann. Rept . 



217 



Butler, Philip A. (ed.) . 1959. 



Annotated bibliography of unpublished estuarine research in the Gulf of 

 Mexico 1925-1959. Gulf States Mar. Fish. Comm. , New Orleans, La., 51 p. 



Contains listings of some general survey papers which may refer to hard clam. 

 No. 2066 is the only specific reference to Mercenaria. The title is listed 

 elsewhere in this bibliography. - J.L.M. 



218 



Butler, Philip A. 1959. 



Growth of New England hard clams in Florida. Proc. Natl. Shellf. Assn. 49, 

 August 1958: ii. 



Listed by title only. M.W.S. and J.L.M. 



59 



