Nutritional value of solitary cells and colonies of Phaeocystis sp. for the bivalve Macoma Balthica (L.)

Abstract

The nutritional value ofsolitary cells and colonies of the flagellate Phaeocystis sp. for the bivalve Macoma balthica was studied in a laboratory experiment. Growth rates and conditions of M. balthica were compared when fed diets of the flagellates Phaeocystis (solitary cells), or Isochrysis galbana, or diets of the diatoms Cylindrotheca clostenum or Chaetoceros socialis. Increase in weight and condition of M. balthica fed Phaeocystis was comparable to that observed with the other algal diets. A high food value for solitary cells of Phaeocystis was suggested by a significantly higher growth per mg added particulate organic carbon and chlorophyll a. In addition, observations on ingestion of Phaeocystis colonies were carried out. Colonies entered inhalant siphons, but were forced out of the siphons immediately, whereas diatom strings entered inhalant siphons without being expelled. It is concluded that solitary cells of Phaeocystis provide suitable food for M. balthica, but that the colony form is without importance as a food source.

Keywords:

• Macoma balthica
• Phaeocystis sp.
• nutrition