Population dynamics and endophytic flora of Chondrus crispus (Rhodophyta) : a temporal study
A temporal long-term study of the population structure and dynamics of the red alga Chondrus crispus at Lilstock, Somerset (Bristol Channel), the British Isles, and an investigation of its associated green and brown endophytic algal flora were undertaken from January 1994 to September 1996. The population of C. crispus was composed of plants which consisted of a basal holdfast from which arose numerous fronds in varying stages of development, with or without reproductive fronds (cystocarps or tetrasporangial sori). Plants were found with only gametophyte (haploid) or tetrasporophyte (diploid) fronds, whereas other plants described as mixed clumps consisted of gametophyte and tetrasporophyte fronds associated with the same basal disc. New plants entered the population and others were lost throughout the study. Individual plant longevity ranged from <46 days to >927 days. The monthly gametophyteitetrasporophyte ratio did not significantly deviate from 1:1, and within the population there was a stable long-lived core of plants, with a gametophyte:tetrasporophyte ratio of 1:1. Gametophyte plants with cystocarps had a significantly greater dry mass and contained a significantly greater number of fronds than tetrasporophyte plants with sori. Significantly higher numbers of tetrasporophytes had reproductive structures (sori) than gametophyte plants (cystocarps) during summer months (namely May, June and July). Both recruitment from spores and frond regeneration from remnant basal discs played an important role in maintaining the population structure. At least 6 green algal taxa including Acrochaete heteroclada, A. operculata, A. repens, A. viridis, Enteromorpha sp(p) and Pseudoendoclonium sp., and at least one brown algal taxon assigned to the genus Streblonema were found in association with gametophyte and tetrasporophyte C. crispus plants with cystocarps and sori, respectively. Spatial distribution of these algae within host tissues ranged from epiphytic through epiendophytic to endophytic. Of the C. crispus plants collected the frequency of plants infected with endophytic algae was reported to reach 95%. Infection by brown algae was rarely found without an associated green algal infection. It is hypothesised that a self-purging natural purification process of infected C. crispus fronds helps rid the plants and population of diseased fronds. It is suggested that it is primarily through the retention of the basal discs that C. crispus is an ecologically successful species.