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 diver sity of nutritional strategies displayed by protists in general, the abilit y of 3 closely associated protists to utilise seaweed carbon was investigat ed. Stereomyxa ramosa, Nitzschia alba and Labyrinthula sp. were cultured wi th seaweed polysaccharides as well as seaweed itself. N. alba and Labyrinth ula sp. were found to utilise seaweed polysaccharides in axenic culture. Al l 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 i n the field is discussed.