Prymnesium parvum Carter (Prymnesiophyceae) in association with macro algae in Ryfylke, southwestern Norway

During summer 1989, a bloom of P. parvum led to loss of approximately 750 tonnes of salmon and rainbow trout in fish farms in Ryfylke. The flagellate was observed densely covering fish nets and various littoral macroalgae in the fjord. Preliminary experiments in laboratory showed that P. parvum grown in nutrient-poor water swam towards Cladophora sp. These observations may indicate heterotrophic use of dissolved organic matter from the macroalgae or from epiphytic diatoms associated with the macroalgae.