spawnings remained localized. In daytime maximum larval concentrations 

 usually were about 1 m below the surface. This concentration moved slightly 

 toward the surface during maximum current velocity. At night larvae were 

 more widely distributed through the water column and the stratum of maximum 

 concentration also descended. - J.L.M. 



276 



Carriker, Melbourne R. 1954. 



Preliminary studies on the field culture, behavior, and trapping of the 

 larvae of the hard clam, Venus (=Mercenaria) meroenaria L. Proc. Natl. 

 Shellf. Assn. 1952: 70-73. 



N.J. annual catch of 5 million lbs of hard clam is taken from a wild crop. 

 If availability of seed could be enhanced, enemies controlled, nutritional 

 and other environmental factors improved, and faster growing, meatier clams 

 bred, crops could be increased many-fold. Studies were made in Little Egg 

 Harbor, N.J. Larvae were obtained by artificial spawning. Various types of 

 substrate were provided. Behavior of larvae changed markedly with age. 

 Swimming stages or veligers (about 98 to 166 u long) were rather uniformly 

 distributed in the water. Older swimming stages had a foot, which was 

 extended as they attempted to contact the substrate. This searching behavior 

 helped to locate favorable setting surfaces. At times they suddenly extended 

 the velum and swam off to another site, where the process was repeated. 

 Searching continued for several days. Pedoveliger (166 to 218 u) is suggested 

 as a name for this stage. During searching a byssus gland in the foot 

 developed rapidly and the clam began weak byssal attachment. Soon the velum 

 was lost and alternate crawling and attachment occurred. Detachment from the 

 byssal thread was rapid and complete. Setting is synonymous with byssal 

 attachment. Crawler is proposed for this stage. In time the byssal gland 

 becomes functionless and the juvenile maintains position with its foot alone. 

 Larvae seem to prefer attachment to a solid surface covered with a thin layer 

 of sediment, then remain suspended in the sediment above. Densest sets were 

 consistently over surfaces coated with thin accumulations of detritus. In 

 clean microdishes clams consistently tried to dig into the glass with the 

 foot. When fine sediment was added they moved vigorously until covered, then 

 ceased locomotion and attached. In absence of suitable sources of contact 

 stimulation crawlers aggregated in grape-like clusters and gained contact 

 with each other. Crawlers in the open reacted strongly to cool light, 

 moving actively as soon as illuminated. Earlier field observations had 

 suggested that larvae select setting sites by differential water currents 

 created by depressions in the substrate, obstacles in path of flow, or 

 variations in bottom topography such as submerged banks of channels. Young 

 set are highly vulnerable to predators. Several types of trap were devised 

 to take advantage of this knowledge. The bottle-top trap was the most 

 successful. A narrow-mouth one-gallon glass bottle 6 inches in diam was cut 

 to remove the bottom about 1/3-way down from the neck. A large paraffined 

 nail in a one-hole rubber stopper was inserted in the neck, and also an 

 8-inch piece of dowelling. Two or 3 shells were placed around the dowelling. 

 Plastic screening with openings 1 mm^ was wrapped over the dowelling and the 

 bottle top and secured. Traps were housed in a special frame which permitted 

 placement in shallow water. (Abstracter's note: the description was con- 

 fusing and difficult to understand; an illustration would have been helpfulj 

 In August, 5 traps caught 483 hard clam seed. Success was attributed to a 

 relatively still pocket of water under a baffle, accumulation of fine layers 

 of sediment, and elimination of larger predators by the screen. The steep 

 upper sides of the bottle may aid in retaining crawlers within the trap, and 

 shallowly sloping lower contours and cultch provide zones at the "shores" of 

 the accumulating pool of sediment, thin enough to attract crawlers. - J.L.M. 



277 



Carriker, M. R. 1955. 



Ecological studies on the hard clam and the oyster in the Gardiners Bay 

 area, April - September 1954. 



Research sponsored by J. and J. W. Elsworth Co. and M. C. Gale. Unpublished 

 sequel to the 1954 report. 



75 



