Influences of a submerged macrophyte on colony formation and growth of a green alga

The effects of the submerged macrophyte Ceratophyllum demersum on the growth and morphology of the green alga Scenedesmus obliquus were assessed by conducting co-culture laboratory experiments (15 and 25 degrees C, presence/absence of 3 g fresh wt of C. demersum per litre of water in S. obliquus culture). Growth rate, photosynthetic pigment-based growth, photo synthetic activity and colony formation of S. obliquus increased in the presence of C. demersum. The proportion of 4-celled colonies of S. obliquus increased from 36 to 76% at 25 degrees C, and from 51 to 71% at 15 degrees C in the presence of C. demersum. The induced morphological shift from unicells to colonies in S. obliquus promoted sedimentation to the bottom-water region, thereby providing a competitive advantage for the submerged macrophyte