VARIATION IN REPRODUCTIVE CHARACTERISTICS OF COLONIES OF THE FRESH-WATER BRYOZOAN CRISTATELLA-MUCEDO

1. We studied relationships between different forms of reproduction an d local variation in the reproductive state of colonies of a common fr eshwater bryozoan Cristatella mucedo Cuvier (Bryozoa: Phylactolaemata) . Four sampling locations in central Finland, including both lotic and lentic habitats, were sampled by scuba diving. The traits studied wer e occurrence of sexual larvae, colony size, number of resting stages ( statoblasts) and number of zooids. 2. While 76.9% of the sampled colon ies carried statoblasts at the time of sampling, only 4.5% of the colo nies were brooding sexual larvae. Most of the colonies were relatively small with a mean colony size of 16.6 mm. 3. In colonies brooding lar vae, the number of statoblasts was positively correlated with the numb er of larvae. We did not detect a colony size threshold for sexual rep roduction or formation of statoblasts. Colonies carrying statoblasts h ad a lower number of zooids per unit dry weight. 4. We found significa nt variation in reproductive traits of colonies among the sampling loc ations, and among lotic and lentic habitats. The observed phenotypic d ifferences may reflect broadly distributed, phenotypically plastic clo nes. Differences in clonal composition of local populations cannot, ho wever, be ruled out and factors that may provide clonal diversity are discussed.