Seasonal and spatial monitoring of productivity and of reproduction of Chondrus canaliculatus (Gigartinales, Rhodophyta) from Chile

Chondrus canaliculatus (C. Agardh) Greville used to cover extensive areas at Puerto Aldea 30 degrees 16' S, 71 degrees 30' W), Tongoy Bay, Chile. The exploitation of this commercially-valuable alga without knowledge of its production behavior and reproductive characteristics led to its severe reduction in the area. Seasonal monitoring of biomass, reproductive capacity and reproductive potential of an intertidal and a subtidal population of C. canaliculatus from this locality was performed in order to gather information on how to manage this resource. Total and fertile frond biomass both have a maximum (4 and 2.5 Kg per m(2) respectively) in spring-summer and a minimum (2.4 and 1.8 Kg per m(2) respectively) during winter. Both were also higher in the subtidal (maxima of 4.2 and 2.6 Kg per m(2)) than in the intertidal population (maxima of 4.0 and 2.6 Kg per m(2)) and carposporic fronds were always more abundant than tetrasporic fronds. Reproductive capacity (based on the number of spores per sorus, the number of sori per frond and the fertile biomass per area unit) followed a similar seasonal pattern reaching a maximum of 5.5 x 10(9) spores per m(2) and was higher in the intertidal than in the subtidal and in tetrasporic rather than carposporic plants. Laboratory studies of spore settlement and survival indicated that the reproductive potential was not different between reproductive phases and between habitats. This potential, close to 30% in relative terms, is similar to those evaluated in other members of the Gigartinaceae. Maxima of total and reproductive biomass, spore production, spore settlement and juvenile survival occurred one to two months earlier in the intertidal than in the subtidal. The data available at this point suggests that the harvesting of the fronds should be done in different periods for the intertidal (early and mid-summer) and the subtidal (mid- to late summer) and approximately a month after the spore productivity peak when these have already been released, assuming that the recovery of biomass is through the growth of new individuals. Further studies on vegetative means of growth and maintenance of the populations should be added to this information in order to propose an adequate management of this resource.