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

Abstract

Mortality and length of development of Balanus eburneus nauplii is modifled in laboratoryculture by both temperature and concentration of unicellular algal food. At 20 and 25�C meanlarval 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 significantlyto 92.5 and 96.5 % at 20 and 25 'C, respectively (p = 0.002 at both temperatures). At 30�C the differencein mortality related to algal food concentration disappeared and mean survival was above 90 % at bothconcentrations. Over the interval of 20 to 30�C, time to complete development to the cyprid stagedecreased 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 foodlevel of 1 X 105 cells ml-l. At 30�C there was no difference between the 2 food concentrations in themedian time to reach the cyprid stage. The hypothesis is proposed that increased algal cell concentrationat 20 and 25�C compensates for lower feeding efficiency and consequently results in bettersurvival. To account for the similarity in development time at 30�C at either food concentration, it isproposed that maximum possible food intake at 30�C is already attained at 1 X 105 cells ml-' and thattherefore increase in the number of algal cells will not further affect development rate to the cypridstage. Experiments on feeding efficiency of B eburneus nauplii in relation to temperature will beneeded to test this hypothesis.