211 



Burbanck, W. D., Madelene E. Pierce, and G. C. Whiteley, Jr. 1956. 



A study of the bottom fauna of Rand's Harbor, Massachusetts: An application 

 of the ecotone concept. Ecol. Monogr. 26(3): 213-243. 



An ecotone is conceived as a tension area always formed when two or more 

 communities are in contact, a zone of great biotic and physical-chemical 

 instability. In the area studied hard clams were free of predation by 

 carnivorous snails, which did not penetrate the harbor, they were harvested 

 on a small scale and irregularly by fishermen. Thus, only general statements 

 could be made about fluctuations in numbers. In summer of 1950 Venus was 

 only about one fifth as abundant as in 1949. The most severe decline was in 

 the shallow muddy north arm where fishermen seldom operate but blue crabs 

 (Callineates sapidus) were most numerous. In summer 1949 these crabs were 

 abundant in Rand's Harbor and in similar estuaries in the Woods Hole area. 

 It was suggested that crab predation rather than overharvesting was responsible 

 for the decline in clam abundance. In summer most Venus had already begun 

 their migration from the channel. Only about one-fourth were in the muddy 

 channel, one half on the gravelly slope, and one quarter at low tide. 

 Substrate inhabited was all combinations of mud, peat, gravel, and sand. Hard 

 clam has a wide range of tolerance for fresh water, which may account for its 

 presence at all tide levels. The Harbor is a man-made estuary about 30 yrs 

 old. Greatest depth is not over 25 ft at high tide. Fresh water flows into 

 both arms. Summer temp was 20 to 23°C, pH 7.0 to 7.6, salinity 27 to 30°/°°. 

 Intensive sampling was done in 4 summers from 1946 to 1950. Venus mercenaria 

 was one of the most abundant organisms. - J.L.M. 



212 



Burnett, Allison L. 1955. 



A demonstration of the efficacy of muscular force in the opening of clams by 

 the starfish, Asterias forbesi. Biol. Bull. 109(3): 355 (abstract). 



A gape of 1 to 2 mm is sufficient for a sea star to insert its stomach between 

 valves of a quahog. Pull required to produce a small gape was recorded by 

 inserting the hook of a spring scale in a notch in the shell of a 2-in quahog. 

 Both adductor muscles were then severed and strong rubber bands, sufficient 

 to withstand a pull greater than that required to open the intact clam, were 

 wrapped around the valves. A sea star of 6- in radius opened the valves a 

 distance of 2 mm within 5 min and held this opening for 3 min. Alternate 

 opening and closing was repeated over a feeding period of 1 1/2 hrs. After 

 about 30 min valves were held open as long as 10 min. The stomach of the 

 sea star does not appear to be damaged when the valves of the clam close. 

 - J.L.M. 



213 



Burnett, Allison L. 1960. 



The mechanism employed by the starfish, Asterias forbesi to gain access to 

 the interior of the bivalve, Venus mercenaria. Ecology 41(3): 583-584. 



Much research has been done on the subject, some investigators believing 

 that the clam is opened by sheer force, others claiming that a toxic 

 secretion is given off. In the 1950s several studies demonstrated that no 

 toxic substance is secreted between the valves, and that the sea star can 

 apply forces of 3,000 to 5,500 g with its tube feet. No author previously 

 had given a complete account of the feeding process. Eight 2-1/2 in clams 

 were bound with heavy cord so that it was impossible to open the valves. 

 All were attacked, and sea stars remained humped over the clams for 8 to 

 4 8 hrs. Clams appeared unharmed: hearts were beating regularly, and 

 adductor muscles intact. Carmine particles introduced into the water 

 failed to enter the valves. In another group of clams a 1 mm2 hole was 

 made at the edge of the valves, which were tied shut. Sea stars were able 

 to insert their stomachs through the notch and digest the clam. Thus, this 

 experiment had no value in testing presence of a toxin. The experiment was 

 repeated, covering the opening with fine bolting cloth. After 2 hrs most 

 clams suffered partial digestion of the mantle, but the rest of the clam 

 was intact. Clams survived, with regular heart beats, for as long as 5 hrs, 

 but eventually were completely digested. There was no evidence of a toxin. 



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