Utilisation of seaweed carbon by three surface-associated heterotrophic protists, Stereomyxa ramosa, Nitzschia alba and Labyrinthula sp.

In view of the abundance of protists associated with seaweeds and the diversity of nutritional strategies displayed by protists in general, the ability of 3 closely associated protists to utilise seaweed carbon was investigated. Stereomyxa ramosa, Nitzschia alba and Labyrinthula sp. were cultured with seaweed polysaccharides as well as seaweed itself. N. alba and Labyrinthula sp. were found to utilise seaweed polysaccharides in axenic culture. All 3 protists were capable of penetrating intact but 'damaged' (autoclaved) seaweed particularly when bacteria were present. The possibility that these and other heterotrophic protists are directly removing macroalgal carbon in the field is discussed.