Dr. Otaiza-O'Ryan, Ricardo

Species of Gelidium are important sources of agar. Mass cultivation of Gelidium spp. has been elusive. Development of techniques to seed thalli in the natural environment could be used to increase in stocks and landings. Gelidium lingulatum is an important seaweed resource in central Chile, growing on the lower levels of exposed rocky intertidal shores. Experiments were done to evaluate fragmentation of the thalli and the effect of some factors on the production of secondary attachment structures (SAS). When experimentally exposed to high water flow, thalli became frequently fragmented, mainly at the level of the creeping axes. Comparisons among parts of the thallus indicated that creeping axes produced more SAS than blades and reproductive branchlets. Similar results were obtained on the three types of substrata tested (rock, barnacle shells, and mussel shells). After 7 days of incubation, more SAS were produced under low than high irradiance (8 and 80 μmol photons m−2 s−1, respectively). Also, a small increase in dissolved calcium (0.5 mM) in the medium enhanced SAS production, but higher levels (2.0 mM) had an inhibitory effect. Higher temperature (15 °C) tended to favor SAS formation when compared to lower temperature (9 °C). For these three factors, differences in the density of SAS were reduced or disappeared after 14 days of incubation. Different seasonal series of each experiment had consistent results. Recommendations are made for the application of these results to seeding of thalli of G. lingulatum on the rocky shore.

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.