ENVIRONMENT AND GROWTH OF THE SOFT CLAM 



287 



to have grown faster than any other group in 

 each test area except Plum Island Sound, the 

 differences in mean growth were analyzed by 

 origins instead of by test areas. Differences 

 between mean growth of groups of clams from 

 different origins were not statistically significant, 

 as shown by table B-4 in appendix B. 



Although not statistically significant, the ap- 

 parently faster growth of Meetinghouse Cove 

 clams in four test areas suggests another factor 

 in the experiment. Clams in Meetinghouse Cove 

 have a history of slow growth. If this were a 

 hereditary or racial characteristic, we should 

 expect them to grow slowly after being trans- 

 planted to other areas. Instead, the growth rate 

 of Meetinghouse Cove clams was numerically 

 greater than that of clams transplanted from other 

 origins. 



On the other hand, native clams in the center of 

 Sagadahoc Bay have a record of fast growth 

 (fig. 2), as indicated by a growth of 14.48 mm. 

 during the present experiment (table 1). In the 

 three test areas where these clams were planted, 

 however, their growth was numerically, although 

 not statistically, less than that of any other group. 

 As far as heredity is concerned, these clams would 

 be expected to have grown fast after transplanting. 

 Since they grew slowly, it is likely that a factor 

 other than heredity was responsible. 



EFFECT OF PREVIOUS ENVIRONMENT 



A possible explanation for the fast growth of 

 Meetinghouse Cove clams and the slow growth of 

 Sagadahoc Bay clams after transplanting is the 

 effect of their previous environment. Meeting- 

 house Cove is a shallow, silty cove on the west 

 side of the Medomak River estuary. Tidal 

 currents are slow, and this area is protected from 

 current -inducing winds by the surrounding hills. 

 There is a high concentration of slow-growing 

 clams in this area, and competition for food must 

 be extreme. 



Sagadahoc Bay is a wide, sandy area exposed to 

 the south winds. Both tidal and wind-induced 

 currents are strong. The clam population consists 

 of a few well-scattered, fast-growing individuals. 

 Competition for food is not likely to be a factor 

 influencing growth in this area. 



Perhaps competition for food causes clams in 

 Meetinghouse Cove to feed more actively or 

 efficiently than those in Sagadahoc Bay which 



have an abundance of food. If this characteristic 

 persisted after the clams were transplanted to new 

 areas, the Meetinghouse Cove clams might be 

 expected to grow faster and the Sagadahoc Bay 

 clams slower, as was observed in the experiment. 



SUMMARY 



1. The objective of the experiment was to 

 determine whether differences in growth rates of 

 soft clams in two parts of one bay (Sagadahoc 

 Bay) were caused by environment or by heredity. 

 This determination is an economically important 

 consideration in clam transplantation. 



2. Test areas were established at five locations 

 along the coast of New England, including the 

 two parts of Sagadahoc Bay. Native clams and 

 clams from two to four other sources were planted 

 in each location. 



3. Growth during one growing season was 

 measured by monthly sampling. 



4. Good survival resulted at Sagadahoc Bay and 

 Bedroom Cove and in two of the three groups 

 planted at Falls Cove. Survival was poor at 

 Robinhood Cove because of depredation by the 

 green crab, Carcinides maenas. For unknown 

 reasons clams died in Plum Island Sound during 

 the late summer. 



5. Mean growth for clams in each test area 

 was as follows: Bedroom Cove, 3.99 mm.; Sagada- 

 hoc Bay, 16.84 mm.; Robinhood Cove, 15.49 mm.; 

 Falls Cove, 3.28 mm.; Plum Island Sound, 19.35 

 mm. 



6. Differences between mean growths in tlie 

 five test areas were highly significant, as shown by 

 analysis of variance. Clams from a single origin 

 grow at significantly different rates when trans- 

 planted to different environments. 



7. Differences between growth rates of groups 

 of clams from different origins within each test 

 area were not statistically significant. Therefore, 

 clams from different origins assume similar growth 

 rates when transplanted to a single enviroimient. 



8. Although not statistically significant, the 

 numerically faster growth of Meetinghouse Cove 

 clams, and the slower growth of Sagadahoc Bay 

 clams in all cases except one, suggest anotlier 

 factor influencing growth. A tentative explana- 

 tion is the effect of previous environment, which 

 caused clams from a slow-growing area (Meeting- 

 house Cove) to grow fast, and clams from a fast- 

 growing area to grow slowly after transplanting. 



