Dispersal of the bryozoan Bugula neritina and effects of adults on newly metamorphosed juveniles

Abstract

In southern California [USA] colonies of the arborescent bryozoan Bugula neritina have a strongly clumped spatial distribution. Small colonies are generally < 4 cm from other small colonies, and witin 10 to 15 cm of large, reproductive colonies. In the laboratory, larvae are capable of swimming for 2 d in the absence of settlement cues. The actual duration of the larval period is reduced to < 2 h when substrata are present, and larvae spend most of their brief presettlement period examining the substratum. Duration of the larval period in the absence of suitable substrata does not vary among larvae from different parent colonies or with temperature. Larvae do not respond to the presence of previously settled juveniles, so the proximity of juveniles to existing colonies most likely represents limited dispersal of larvae in the presence of abundant field settlement cues. To assess the effects of adults on young bryozoans, day-old juveniles were transplanted into the field with and without adult colonies present. There were no consistent effects of adult colonies on either growth or survival of juveniles. Suvivorship varied among 3 experimental sites, but was unaffected by the presence of adults. High mortality of adult colonies was accompanied by high juvenile mortality. Growth rates of juveniles were affected significantly by adults, but in no consistent way. At one site, juvenile growth was higher beneath a canopy, at the second, growth was lower, while there was no difference at the third site.