The solitary bryozoan,Monobryozoon limicolaFranzén (Ctenostomata), a comparison of mesocosm and field samples from Oslofjorden, Norway

Subtidal sediment was sampled and transported in boxes into an indoor mesocosm to establish a soft-bottom community for experimental studies. After seven months 662 individuals of the solitary bryozan, Monobryozoon limicola, were found inside the mesocosm in 6 of 24 cores (inner diameter 6 cm). This is the first record of M. limicola in Norway. The mean number of specimens per corer was 27.5 with a highly aggregated distribution. The number of other organisms in the cores with M. limicola was significantly lower than in cores were M. limicola was absent. M. limicola was not found at the site from were the sediment in the mesocosm originated. It is proposed that the high density in the mesocosm is a function of reduced competition, predation or disturbance from organisms found in the field but not in the mesocosm.