1538 



Rhoads , Donald C.,and Giorgio Pannella. 1970. 



The use of molluscan shell growth patterns in ecology and paleoecology . 

 Lethaia 3(3) : 143-161. 



In Mercenaria mercenaria, winter rings on the shell can be distinguished 

 from disturbance or spawning rings because they occur after a gradual 

 decrease in shell concavity. Juvenile hard clams grown in holding tanks 

 were notched and transplanted to the intertidal zone in Milford, Conn., 

 and then to subtidal of Buzzards Bay, Mass. Microgrowth patterns of dam 

 shells recorded the transplant sequence. Growth decreased after transplant 

 to intertidal and from intertidal to surface of turbid mud subtidal bottom. 

 Growth increased from intertidal to subtidal in clams elevated above turbid 

 mud bottom. Growth was greater in sand than mud in all areas. Hard clams 

 deprived of substratum exhibited change in microgrowth patterns such as: 

 large varices; periostracal extensions; and sharply delimited daily growth 

 bandings. - D.L. 



1539 



Rhoads, Donald C., and David K. Young. 1970. 



The influence of deposit-feeding organisms on sediment stability and community 

 trophic structure. J. Mar. Res. 28(2): 150-178. 



Juvenile Mercenaria mercenaria one summer old from Milford, Conn., were marked 

 and planted in mud and sand in plastic trays. One tray was held in the 

 intertidal zone, 3 were planted in- water 20 m deep on a 3-tiered platform. 

 The bottom of the deepest tray was 10 cm above, the others were 4 5 cm and 

 75 cm above bottom in Buzzards Bay, Mass. The control tray was held at 

 Milford, Conn. Control and the deep tray clams grew at the same rates, adding 

 about 0.6 mm in 64 days. Clams in the middle tray added about 1.1 mm, and in 

 the upper tray about 1.3 mm. The 3 experimental trays were above a mud bottom 

 burrowed by deposit feeders. Differential growth was measured by shell growth. 

 Hard clams feed only when valves are open and shell deposition takes place only 

 during periods of valve separation. Therefore, hard-tissue growth reflects 

 metabolic activity. During extended periods of starvation soft-tissue growth 

 may be negative, while net hard-tissue growth, although small, is positive. 

 Intensive reworking of the upper few cm of a mud bottom by deposit feeders 

 produces a fluid fecal-rich surface easily resuspended by low-velocity tidal 

 currents. It is suggested that the physical instability of this surface tends 

 to clog the filtering structures of suspension-feeders like hard clam, bury 

 newly settled larvae or discourage settling of suspension-feeding larvae, and 

 prevent sessile epifauna from attaching. This could explain the marked 

 spatial separation of suspension-feeders (which are largely confined to sandy 

 or firm mud) and deposit-feeders (which attain high density on soft, muddy 

 bottom) . - J.L.M. 



1540 



Rhoads, Donald C, Kenneth Tenore, and Mason Browne. 1975. 



The role of resuspended bottom mud in nutrient cycles of shallow embayments . 

 In Estuarine Research. Vol. 1. Chemistry, Biology, and the Estuarine 

 System. L. Eugene Cronin (ed.). Academic Press, Inc., New York: 563-579. 



The bottom of Buzzards Bay, Mass. below a depth of about 13 m is dominated by 

 silt-clay sediment. A turbid-water layer, created by tidal-current scour, 

 extends about 3 m above the bottom, and sometimes higher. Trays of 

 Mercenaria mercenaria were placed on the bottom in 20 m of water within the 

 turbidity layer. Clams had higher growth rates than populations grown 

 nearshore. Details are contained in other papers by the senior author 

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



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