CREASER and CLIFFORD: LIFE HISTORY STUDIES OF SANDWORM 



water or exposing themselves on the surface of 

 the mud, and are therefore subject to greater 

 natural mortality through predation. The free- 

 swimming habits of Nereis virens (especially at 

 night) have been well documented (Crowder 

 1923; Gustafson 1953; Dean 1978). Brafield and 

 Chapman (1967) reported that by the onset of 

 spawning, males and females occurred in about 

 equal numbers. Snow (1972), on the other hand, 

 reports a 3:1 ratio of males to females prior to 

 spawning. 



Oocyte Development 



Some similarities exist between our studies of 

 oocyte development (see Figure 4 A) and those of 

 Brafield and Chapman (1967) and Snow and 

 Marsden (1974). Brafield and Chapman (1967) 

 reported that ovulation occurred in February or 

 March at 50 n and the oocyte diameters increased 

 from 80 /j. to 160 p. during the period of rapid 

 growth between September and December. The 

 increase in oocyte diameters to 170-180 n prior to 

 spawning required about 14 mo. Snow (1972) re- 

 ported that the smallest eggs found free in the 

 coelom of Nereis virens measured 10 /i in diame- 

 ter. The eggs usually remained in clumps until 

 they measured 25 m and appeared singly above 

 50 m- Snow and Marsden (1974) stated that the 

 rapid-growth phase began in September, and 

 their egg growth figure showed that this ex- 

 tended at least until December. They stated that 

 maturation required 1-2 yr, depending upon the 

 time of year when the eggs were produced. Ova 

 measured 210-240 /j. when spawned in May. 



The standard deviation for oocyte diameters 

 recorded in both the present study and that of 

 Brafield and Chapman (1967) reveals that small 

 oocytes are more variable in size than large 

 oocytes. The large standard deviation for small 

 oocytes results from ovulation occurring over a 

 long period. Eventually, the maturation rate of 

 oocytes produced late in this period accelerates 

 so that all oocytes mature at a certain size at 

 the same time (Clark cited in Stancyk 1979). 

 Similar observations have been recorded for 

 Nereis diversicolor Muller (Clark and Ruston 

 1963). 



Oocyte development in Nereis virens follows 

 the typical sigmoid growth curve. Similar obser- 

 vations have been recorded for all or part of the 

 oocyte maturation processes in Arenicola marina 

 Linnaeus (Howie 1964 pers. commun. cited in 

 Clark 1965), Nereis diversicolor (Clark and 



Ruston 1963), and Glycera dibranchiata Ehlers 

 (Creaser 1973). 



Although no length measurements were ob- 

 tained for the sandworms used in Figure 4A, it 

 was generally evident to us that no relationship 

 existed between size of the adult and size of the 

 eggs; potential spawners of all sizes at one time 

 possessed eggs of similar size. 



Numbers of Eggs Laid 



Sandworms >37 cm long were not found in the 

 Wiscasset closed area (Creaser and Clifford foot- 

 note 6). However, a few larger worms, up to 54 

 cm long, were captured adjacent to the closed 

 area after extensive digging, and egg counts 

 from these as well as the more typical sizes were 

 included in this study. Sandworms contained 

 considerably fewer eggs than were found in simi- 

 lar-sized bloodworms, Glycera dibranchiata, col- 

 lected from the same closed area but higher on 

 the flat (Creaser 1973). The relatively large num- 

 bers of eggs produced (0.05-1.3 million), however, 

 are consistent with the observation that macro- 

 fauna species generally produce large numbers 

 of gametes (Thorson 1950 cited in Coull 1979). 



Environmental Conditions During 

 Spawning 



Clark and Olive (1973) reported that "In the 

 family Nereidae, sexual maturation and epitoky 

 are caused by a decline in the rate of production 

 of a cerebral hormone." Clark (1965) suggested 

 that changes in the secretion rate of cerebral 

 hormone might be controlled by environmental 

 conditions or by some feedback mechanism. A 

 distinction is made between (a) necessary envi- 

 ronmental conditions and (b) specific environ- 

 mental signals (Clark cited in Stancyk 1979). 



Results of the present study suggest that a 

 water temperature of about 7°-8°C might be one 

 of the necessary environmental conditions re- 

 quired to initiate spawning. This hypothesis is 

 strengthened by the fact that Snow and Marsden 

 (1974) successfully fertilized Nereis virens ova 

 and reared the young in the laboratory at 7°C. 

 Sveshnikov(1955) recorded that surface temper- 

 ature varied between 8.9° and 9.5°C at time of 

 spawning in the White Sea. Some investigators 

 (Thorson 1946; Korringa 1957) have reported 

 that a rise in seawater temperature triggers 

 spawning in a number of marine organisms. Bass 

 and Brafield (1972) induced premature spawn- 



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