Observations on Ceramium tenuicorne (Rhodophyta) and its reproduction

Ceramium tenuicorne (Kützing) Wærn (including C. gobii Wærn) is a common red alga in the Skagerrak-Baltic Sea region. A Polysiphonia-type of life history and asexual reproduction by paraspores, previously demonstrated in cultures for this species, have been confirmed. In addition, a characteristic kind of reproductive structure (‘Gobi’s monosporangia’) bas been described in field-collected material from the Baltic Sea. This type of structure was used by Wærn (1992) to distinguish his new species Ceramium gobii. We studied the formation and function of ‘Gobi’s monosporangia’ in culture and found them to be modified branch apices in which cells transformed directly into enlarged rounded bodies that detached and grew into a new generation of similar plants. They are referred to as vegetative propagules rather than sporangia. Tetrasporangia were occasionally found on the same individuals that bore either parasporangia or vegetative propagules. The tetraspores from these plants usually failed to develop, but in a few cases mature gametophytes developed, as well as plants with mixed spermatangia and parasporangia or spermatangia and vegetative propagules. Thus an interconnection between sexual and asexual modes of reproduction was demonstrated.