Variation in Growth Rate and Reproduction of the Bryozoan Bugula neritina

¹ Department of Zoology, University of Melbourne, Parkville, Victoria 3052 Australia

Colonies of the arborescent cheilostome bryozoan Bugula neritina vary dramatically in their growth rate even when in apparently identical microhabitats. Comparison of growth rates of juveniles derived from four parent colonies at each of two sites showed only weak effects of parental colony on juvenile growth. These effects accounted for at most only 5.4% of total variation in growth. Variation in growth, and hence age at first reproduction, is interpreted as a plastic response of colonies to fine-scale environmental variation.

Bryozoans from seagrass meadows mature at a smaller size than those colonies from nearby rocky reefs (1200, vs. 3500 zooids at first reproduction, respectively). When juveniles from both of these habitats were grown in a common garden, there was, again, no variation among parental groups, but a highly significant effect of origin of juveniles. Juveniles matured at a size similar to that seen in their parental population, indicating that genetic or very early maternal effects influence timing of reproduction.

A post hoc test of the effect of onset of reproduction on colony growth showed no reduction in growth rate. Instead, colonies that reproduced grew faster than similar aged and sized colonies that did not reproduce.