Zeldis et al.: Development of Hoplostethus atlanticus eggs in the water column 



377 



ascent rate (mean of 350 m-day -1 ; Fig. 3) at 6.0°C 

 and 35.00 ppt in the experimental cylinder. This den- 

 sity (1.02406 g-cm -3 ) and the coefficient of thermal 

 expansion were then used to estimate the ascent 

 rates (Table 1) for stage 1-11 eggs through the wa- 

 ter column. This was done for depth strata corre- 

 sponding to 1°C increases, from 6.0 (the bottom at 

 870 m) to 11.25°C (the bottom of the mixed layer at 

 250 m). The analysis accounted for the change in 

 density of the eggs (via the coefficient of thermal 

 expansion), change in density of the surrounding 



water (from MOCNESS-CTD data), and change in 

 seawater viscosity, as the eggs ascended the water 

 column. Neither the viscosity or coefficient of thermal 

 expansion were corrected to account for changes in sa- 

 linity and pressure during the ascent ( p. 69 in Sverdrup 

 et al., 1964; Table 3.2 in Neumann and Pierson, 1966) 

 because they both changed less than 5% over the sa- 

 linity and pressure gradients considered here. 



Ascent rates of early to mid gastrula and mid to 

 late embryo stages (stages 15-25) were estimated in 

 the cylinder at surface temperature (11-12°C) and 



