Significance of Temperature to Larval Survival and Length of Development in Balanus ebumeus (Crustacea: Cirripedia)

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 25C 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 30C 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 30C, 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 30C 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 25C compensates for lower feeding efficiency and consequently results in better survival. To account for the similarity in development time at 30C at either food concentration, it is proposed that maximum possible food intake at 30C 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. ' This paper is dedicated to the memory of Dr Harold Barnes who made so many important contributions to the ecology and physiology of Cirripedia " Contribution Number 4950 from the Woods Hole Oceanographic Institution 0 Inter-Research/Printed in F. R. Germany