Mortality and length of development of Balanus eburneus nauplii is modifled in laboratory culture by both temperature and concentration of unicellular algal food. At 20 and 25°C mean larval survival was 63.5 % and 66.0 %, respectively, at an algal concentration of 1 X 10' cells ml-l. When the algal concentration was doubled to 2 X 105 cells ml-' mean survival increased significantly to 92.5 and 96.5 % at 20 and 25 'C, respectively (p = 0.002 at both temperatures). At 30°C the difference in mortality related to algal food concentration disappeared and mean survival was above 90 % at both concentrations. Over the interval of 20 to 30°C, time to complete development to the cyprid stage decreased from a median of 7.6 to 3.9 d at 2 X 105 cells ml-' and from 10.8 to 3.9 d at the lower food level of 1 X 105 cells ml-l. At 30°C there was no difference between the 2 food concentrations in the median time to reach the cyprid stage. The hypothesis is proposed that increased algal cell concentration at 20 and 25°C compensates for lower feeding efficiency and consequently results in better survival. To account for the similarity in development time at 30°C at either food concentration, it is proposed that maximum possible food intake at 30°C is already attained at 1 X 105 cells ml-' and that therefore increase in the number of algal cells will not further affect development rate to the cyprid stage. Experiments on feeding efficiency of B eburneus nauplii in relation to temperature will be needed to test this hypothesis.

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