Growth and reproduction of the red alga Rhodomela larix

Components of the growth and life history of the red alga Rhodomela larix (Turner) C. Agardh were studied during an 18-month period at a high intertidal and a low intertidal site on the central Oregon coast. Growth was measured by following (i) individually marked upright axes, (ii) clumps of axes thought to represent individual plants, and (iii) large patches of R. larix. Variation in size and growth was common among axes, and portions of some axes were clearly perennial. Plants grew most rapidly in the spring and summer (up to 1.2 mm/day) with a large amount of variation occurring between and within zones and among seasons. Overall, plants at the higher site were shorter and had fewer branches during most of the year than plants at the lower site. Gametophytes were more common in the higher site, while tetrasporophytes predominated at both sites. Reproductive axes were present throughout the observation period, although little recruitment of sexual propagules was seen, implying that populations may be maintained by vegetative perennation of individual plants.