There is a progressive reduction in thickness of daily growth bands from the 

 center of the Bay to the creek in which effluent is discharged. Thermal 

 effects are not evident when water temperatures are lower. In summer the 

 effect is seen in clams within a 1.6 km radius of the discharge creek. 

 Summer growth of transplanted clams was reduced by 60 to 90% after trans- 

 plantation to the discharge site, as compared with growth in their natural 

 environment. Optimum temperature for growth of M. meroenaria is about 20°C. 

 Temperatures at the bottom in the mouth of Oyster Cr. (effluent) ranged from 

 28 to 34 °C. Thermal discharges also occasionally interrupt the daily growth 

 process. Breaks in growth occur suddenly and appear as large V-shaped 

 indentations in outer prismatic shell layer, when rapid changes in water temp 

 occur (as much as 5°C within several hours) . Such breaks are followed by 

 extremely thin increments, demonstrating severe physiological shock. These 

 breaks were most frequent in clams close to the effluent and the number per 

 clam decreased sharply in all directions away from the thermal plume. No 

 thermal-shock breaks were found more than 1.6 km away. A large part of the 

 clam population within the affected area monitors every major operational 

 change at the power plant. The effect on the Bay as a whole is minimal, 

 because severe effects are confined to an area with radius about 0.8 km. 

 Hard clam is an economically feasible and practical indicator organism for 

 monitoring effects of thermal discharges and many other environmental 

 variables in the coastal zone. - J.L.M. 



990 



Kennish, Michael J., and Richard K. Olsson. 1975. 



Effects of thermal discharges on the microstructural growth of Meroenaria 

 meroenaria. Environmental Geol . 1: 41-64. 



Temperature increase has had an effect on Meroenaria meroenaria living 

 within the limits of the stressed area. Analysis of growth increments on 

 the valves of 3- and 4-yr olds gave the following conclusions: 1) subdaily, 

 daily, bidaily, tidal (fortnightly), monthly, and annual periodicity growth 

 patterns were reflected; 2) summer growth in areas affected by thermal 

 effluent were lower than in areas unaffected; 3) in Meroenaria unaffected 

 by effluent growth was greatest in summer, least in winter; 4) growth was 

 higher in sands than in muds; 5) Meroenaria in Barnegat Bay grew most 

 rapidly in the second yr; 6) growth cessation in the Bay corresponded to 

 summer (heat) shocks, winter (freeze) shocks, thermal shocks, major storms, 

 spawning periods, neap tides, and local disturbances of unknown origin; 

 7) more than 80% of all growth breaks were shock breaks related to periods 

 of temperature stress; 8) thermal-shock breaks were conspicuously developed 

 in, and restricted to, Meroenaria subjected to thermal effluent; these 

 breaks accounted for most of the growth breaks at the mouth of Oyster Creek; 



9) shutdowns, massive load reductions, and rapid renewal of operations at 

 the generating station correlate exactly with thermal-shock breaks; 



10) spawning occurred in June and early July when water temps were rising 

 from 21° to 25°C; 11) spawning breaks were absent for 1971 and 1973 from the 

 microstructure of the clams most strongly affected by thermal effluent; and 

 12) growth breaks occurred most frequently in old Meroenaria . Growth in 

 Meroenaria is strongly dependent on environmental factors, and temp is the 

 most important. Quahogs affected by thermal effluent are adversely affected 

 by temp extremes and by temp fluctuations. It is suggested that shutdowns 

 of the nuclear power station be made in fall as far as possible to avoid 

 chance overlap of spawning, and shutdowns or renewals of operations be made 

 over a span of at least a week. More research is needed to determine the 

 effects of substrate and food supply on growth. Also future research 

 should determine whether mortality is related to effluent or is unrelated. 



- J.L.M. 



991 



Kerfoot, William B., and S. Andrew Jacobs. 1976. 



Cadmium accrual in combined wastewater treatment-aquaculture system. Envir. 

 Sci. Technol. 10(7): 662-667. 



Trace amounts of Cd were introduced in isolated links in the sewage/seawater- 

 plankton-shellf ish food chain at Woods Hole. The phytoplankton species 

 Prasinoaladus trioornutum, and a mixture of diatoms dominated by Phaeodaotylum 

 triaornutum and Chaetoceros simplex , increased rapidly in metal concentration 



277 



