In the presence of a suitable substratum the lecithotrophic larvae of the bryozoan Bugula flabellata preferentially settle within the first six hours after hatching, whereas a marginal percentage of them (approximate to 1%) delay settlement between 6 and 24 h after larval release. In the present study we report that larvae of B. flabellata forced, by mechanical water shaking, to delay their settlement from 6 to 57 h, significantly reduced their fitness. Bugula flabellata larvae keep their capacity to settle in a level near to 95% during the first 24 h after release. Hereafter only 30% of the larvae forced to delay settlement for 24 to 48 h was able to settle. Furthermore, larval metamorphosis quickly decreased from an initial approximate to 100% value to less than 50% after 6 h of a forced delayed settlement. Colonies generated by larvae forced to delay settlement for 48-54 h generated colonies that after 21 days of growth had in average a smaller number of zooids than colonies generated by larvae forced to swim for only 1-6 h (7.6 +/- 1.88 and 12.7 +/- 1.02, respectively). The lethal and sublethal effects generated by delaying larval settlement on the metamorphosis success of B. flabellata correlate well with the larval behaviour of settling soon after release. The lethal and sublethal effects of delaying settlement in species producing lecithotrophic larvae are likely to be a mayor selective force favouring larval release in low water movement conditions.