Dr. Otaiza-O'Ryan, Ricardo

Variability in thallus morphology is common in red seaweeds. Two co-occurring forms have been described for Chondracanthus chamissoi based mainly on blade width. To determine whether two distinct forms or a range of intermediate morphologies occur in C. chamissoi, thalli were collected from three localities in southern Chile in autumn–winter, repeating the sampling in one locality in spring and in summer. In each occasion, individual sporophytic and male and female gametophytic clumps were collected, and the longest blade with intact apex from each clump was evaluated. Blade length, width, density of spines, axis curvature and thickness, and pinnule length and width were evaluated in each blade. Principal components analyses separated two groups of thalli, one group with narrow, thick, and curved (concavo-convex) blades, with few spines consistent with f. lessonii, and another with broad, thin, and flat blades, with many spines consistent with f. chauvinii. These variables also had bimodal frequency distributions. Pinnule measurements were mainly associated with differences among sporophytes and gametophytes. Age (length), phase of the life cycle, and sex were not related to the forms. Furthermore, thalli of both forms were collected side by side in the study sites and throughout the year so the occurrence of the two forms was not attributable to local environmental conditions. In this species, secondary basal disks are produced after attachment of apexes to the substratum. These disks may produce blades with a modified morphology in a way similar to proliferations and regenerations described for Schottera nicaeensis.

Fragments of Chondracanthus chamissoi have the capacity of secondary attachment. In the laboratory, apexes of upright branches of C. chamissoi placed 1–2 mm and parallel to horizontal substrata underwent morphological transformation prior to becoming attached, changing from thick and blunt to elongated and cylindrical and from straight to curved towards the substratum, where they eventually produced secondary attachment discs. When transformation occurred, signs could already be observed after 3 days of incubation. Several factors that could affect transformation and attachment were tested. The vertical or horizontal orientation of the fragments, the angle of incidence of light, and the phase of the life cycle had no effect on transformation, whereas the presence of reproductive structures had a negative effect compared to vegetative fragments. Low light intensity and low water flow favored the transformation response. Calcareous substrata (bivalve shells and coralline crusts) produced the highest frequency of transformation and other solid substrata (glass slides, rock, and sea-squirt tunic) followed in the ranking, but fleshy seaweeds (Ulva sp., Sarcothalia crispata, and C. chamissoi) failed to produce any response. Thus, the experimental upright branches developed features and reactivity similar to basal branches when the former were placed in conditions similar to those where the latter occur in the natural environment. Vegetative reproduction has been incorporated in cultivation techniques of C. chamissoi, but it could also be used in repopulation or restoration programs of this species.