Macrocystis pyrifera (L.) Ag. in Tasmanian Waters

Abstract

An account is given of the taxonomy and distribution of Macrocystis in Australian waters, the development of the plant is outlined, and beds on the east coast of Tasmania are described.

Measurements of growth indicate that the most rapid elongation of the stipe takes place near the apex, and that a stipe may increase in length at a rate of at least 3.4 cm per day. The life of a stipe is estimated at between 7 and 10 months. Experiments show that the apical blade with a portion of the stipe may sometimes continue growth when severed from the holdfast. It is found that decrease in length of a blade caused by decay of tissue at the apex is for a time made good by meristematic activity near the base of the blade, but that finally meristematic activity ceases and decay eventually removes the whole blade.

Harvesting of Macrocystis pyrifera (L.) Ag. in selected areas over 2 yr gave no indication that beds are adversely affected by cutting the stipes 3 ft. below the surface at approximately 4-monthly intervals. The average yield obtained in three localities over 2 yr was 4 tons/ac, and on this basis the area surveyed could be expected to yield approximately 355,000 tons of wet weed or 35,000–44,000 tons of air-dried weed per year. Analyses of monthly samples of Macrocystis show an average alginic acid content of approximately 21 per cent. and an average mannitol content of approximately 8.7 per cent. on a dry-weight basis.