Field and culture studies of Desmarestia aculeata (L.) Lamour

The life history and development of Desmarestia aculeata were followed in both field and culture studies. Zoospores released from macroscopic sporophytes gave rise to microscopic gametophytes, whose gametes in turn gave rise to sporophytes equipped with trichothallic meristems. Growth ceased when the meristems were shed and in the following quiescent phase secondary tissues developed. This phase was terminated by the onset of reproduction and regeneration.Statistical analyses carried out on monthly samples showed marked seasonal changes in plant behaviour. New sporophytes appeared in spring and grew rapidly until mid-summer when meristems were shed. Reproduction of sporophytes began in November and was followed in December by the onset of regeneration. During the winter sporophytes on unstable substrata were usually lost, whereas microscopic stages survived. Sporophytes on stable substrata were usually perennial. This sequence was confirmed on marked plants.On a world scale, the species ranges from latitude 40°N to 80°N. The vertical distribution of stable populations of D. aculeata is restricted to deeper water below the major laminarian species.The effects of heavy growths of plant and animal epiphytes are thought to be restricted to reduction of available light and mechanical breakage of thalli.