Abstract Seasonal variations of carrageenan percentage and other biochemical properties for estuarine and open coastal populations of Chondrus crispus Stackhouse were recorded monthly during 1972–1973. Gel strengths, viscosities and percentage of carrageenan exhibited maximum values in the autumn and early winter. An inverse relationship was recorded between total carbohydrates, as well as carrageenan and proteins. Protein levels were highest when nutrients (nitrogenous) were highest and vice versa. Differential gelling properties occur in the tetrasporic and gametophytic stages of Chondrus. Lambda carrageenan, the non-gelling fraction, occurs in tetrasporic plants. Spatial variations of fractions may also be associated with exposure to wave action, for tetrasporic plants are primarily restricted to the subtidal zone, except at very exposed open coastal sites.