Bay scallop, continued 



Substrate : Late larval/early juvenile stages use vari- 

 ous substrates for attachment, including oyster shells, 

 rope, algae, seagrass, and submerged macrophytes 

 (Gutsell 1930, Marshall 1947, Marshall 1960, Thayer 

 and Stuart 1974, Fay et al. 1983). Seagrasses, such 

 as eel grass (Zostera marina) and shoal grass (Halodule 

 wrightii), appear to be the preferred settling site given 

 the abundance that is often associated with seagrass 

 habitats (Belding 1910, Gutsell 1930, Sastry 1962, 

 Thayer and Stuart 1974, Castiglione pers. comm.). 

 However, if seagrass density is too great, current 

 velocity is reduced and bay scallop abundance may 

 decline (MacKenzie 1989). Scallops can settle and 

 survive in areas lacking seagrass (Marshall 1947, 

 Marshall 1960), but individuals <10 mm generally 

 cannot tolerate silty substrates (Castagna 1975), and 

 burial can occur in muddy substrates (Tettelbach et al. 

 1990). Smith et al. (1988) have demonstrated that 

 transplanted seagrass does not serve as a highest 

 quality habitat, due to greater losses from predation 

 and/or transport as compared to a natural seagrass 

 site. 



Physical/Chemical Characteristics : 

 Temperature: Eggs and larvae are stenothermal, with 

 15 to 20°C required for early development. Optimal 

 embryonic development occurs from 20 to 25° and 

 best larval growth from 25 to 30°C (Tettlebach and 

 Rhodes 1 981 ). Wright et al. (1 983, 1 984) found larvae 

 subjected to temperatures below the spawning tem- 

 perature experienced a cold-shock which resulted in 

 higher mortalities. Juveniles and adults are euryther- 

 mal, and Connecticut bay scallops are reportedly able 

 to tolerate temperatures as low as -6.6°C for short 

 periods (Marshall 1 960). Throughout their range they 

 occur in areas where summer maximum water tem- 

 peratures do not exceed 32°C (Sastry 1965, Barber 

 and Blake 1983). 



salinities on scallop behavior indicated that at salinities 

 of 16%o and temperatures of 10° to 15°C the animals 

 became inactive, and at 20° to 25°C reduced activity 

 occurred at 22%, and 1 8%o (Duggan 1 973). Mortality of 

 scallops has been demonstrated in the laboratory at 

 salinities of 10% o and less over a range of temperatures 

 (Mercaldo and Rhodes 1982). 



Dissolved Oxygen: Oxygen resting requirements of 70 

 ml/kg/hour at 20° have been reported (Van Dam 1 954). 

 Critical dissolved oxygen (DO) concentrations for this 

 species may be related to individual size and ambient 

 water temperature (Voyer 1992). 



Other: Turbidities greater than 500 ppm may interfere 

 with normal growth and reproduction (Fay et al. 1 983). 

 Water currents can displace scallops from their "home" 

 habitat, and current velocity can have effects on growth 

 related to food availability (Moore and Marshall 1967, 

 Kirby-Smith 1972, Rhodes 1991). An optimal amount 

 of current is necessary to maintain high concentrations 

 of suspended food and remove waste materials rapidly 

 (Kirby-Smith 1972). 



Movements and Migrations : Egg and early larval 

 stages may be transported by tidal currents. Late larval 

 stages are capable of swimming by use of the ciliated 

 velum and crawling with the foot (Gutsell 1 930, Sastry 

 1965, Hall 1984). Juvenile and adult scallops are 

 capable of swimming via propulsion created by the 

 clapping of the two valves (Belding 1910, Gutsell 1 930, 

 Moore and Marshall 1967). This ability apparently 

 serves to maintain position in grassbeds and avoid 

 competitors and predators (Peterson et al. 1 982, Win- 

 ter and Hamilton 1985). The extent of late juvenile and 

 adult movements is unclear. There are, however, 

 some reports of scallops migrating in mass (Roessler 

 and Tabb 1 974). 



Salinity: Eggs and larval stages are generally found in 

 polyhaline salinities (18 to 30%o), and egg and larval 

 development are most successful within that range. In 

 laboratory studies, normal embryo development oc- 

 curs over a narrow range of salinities. Egg develop- 

 ment was successful at 25%o, but no embryo develop- 

 ment occurred at 1 or 1 5%° (Castagna 1 975, Tettlebach 

 and Rhodes 1981). Larvae develop at salinities from 

 20 to 35%o with optimal development at 25%o (Tettlebach 

 and Rhodes 1981), and are not found below 22%o. 

 Although they tend to occur in higher estuarine salini- 

 ties (15-30%o), juveniles and adults are considered 

 euryhaline and can tolerate moderate salinities. How- 

 ever, symptoms of stress appear when salinities drop 

 below 16%o (Sastry 1966, Duggan 1973). The mini- 

 mum salinity determining overall distributions is ap- 

 proximately 14%o (Belding 1910, Gutsell 1930). Labo- 

 ratory experiments examining the influence of reduced 



Reproduction 



Mode : Bay scallops are hermaphroditic, usually 

 protandrous (Peters 1978), and semelparous (Bricelj 

 et al. 1987). Fertilization is external, in the water 

 column or on the bottom. Male gametes are generally 

 (but not always) released before female gametes, 

 reducing the chance of self-fertilization (Belding 1910, 

 Gutsell 1930, Loosanoff and Davis 1963, Hall 1984). 



Spawning : Spawning is influenced by temperature, 

 photoperiod, salinity and food abundance (Sastry 1 975). 

 It occurs in estuaries and in nearshore areas at various 

 times throughout the range. In the New England area, 

 spawning is triggered by increasing temperatures 

 (Belding 1910, Cooper and Marshall 1 963, Taylor and 

 Capuzzo 1983), while spawning south from North 

 Carolina is triggered by decreasing temperatures (Bar- 

 berand Blake 1983). In Florida, spawning begins with 



15 



