THE EFFECT OF CELL CONCENTRATION ON COLONY GROWTH AND FEEDING IN THE BRYOZOAN CELLEPORELLA-HYALINA

The effects of cell concentration on colony growth and feeding behavio ur were investigated in the polymorphic marine bryozoan Celleporella h yalina (Bryozoa: Cheilostomata) under controlled, laboratory condition s. We compared the relative zooidal composition of colonies cultured o n Rhodomonas baltica (Karsten) for seven weeks at 18-degrees-C. We obs erved the pharynx of active lophophores on sudden exposure to high cel l concentrations, and recorded the length of feeding episodes and inge stion rates. Colonies grew, reproduced and produced viable larvae at a ll levels of food supply, but performed optimally at 50-100 cells mul- 1. Cell concentration influenced somatic parameters more than sexual, the latter being more closely associated with genotype. Relative somat ic investment was greatest at 10 cells mul-1 and least at 50 cells mul -1. The frequency of ovicells containing larvae remained at about 74% irrespective of food supply. Basal male investment was greatest at 10 cell mul-1, frontal male investment at 50 cells mul-1, and female inve stment at 100 cells mul-1. Cell ingestion rates of previously starved zooids increased as a function of cell concentration, with an inverse relationship between length of feeding episode and concentration. Food particles were drawn from below the lophophore by lateral cilia, cili ary reversal brought them over the mouth, and ingestion then resulted from a pharyngeal current. These results suggest that, on exposure to high cell concentrations, bryozoans may exhibit specific behaviour.