Browsing by Author "LUXORO, C"

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    ADDITIONAL EVIDENCE FOR ECOLOGICAL DIFFERENCES AMONG ISOMORPHIC REPRODUCTIVE PHASES OF IRIDAEA-LAMINARIOIDES (RHODOPHYTA, GIGARTINALES)
    (1989) LUXORO, C; SANTELICES, B
    Gametophytes are more abundant than sporophytes in wave exposed rocky intertidal populations of Iridaea laminarioides Bory in Central Chile. In this study we experimentally tested the differential effects of selected ecological factors on karyologically different life history phases. In the field, gametophytes dominated at higher elevations and during summer; tetrasporophytes were most abundant low in the intertidal and during the fall. Laboratory responses correlated with these patterns. Gametophytes exhibited greater desiccation tolerance than tetrasporophytes. Optimum growth of gametophytes occurred at higher temperatures (20.degree. C) and longer photoperiods (16:8 h LD) than sporophytes (15.degree. C and 12:12 h LD). Grazing preferences changed with the developmental stage of the alga, but all herbivores tested had increased preference for diploid tissues as compared to haploid. Number of spores produced with respect to total plant surface, or total rocky surface, or settlement of spores and their germination rate did not show significant differences between phases but showed great variability in space and time. Spontaneous spore release, however, was always higher in cystocarpic than in tetrasporangial thalli. Such a combination of results suggests tht some real ecological differences exist between the two life history phases of I. laminarioides. Such ecological differences permit a prediction of vertical and temporal patterns of distribution for both phases. Horizontal Horizontal patterns of distribution cannot be explained because the several selection factors probably interact differently in various habitats.
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    GALLERIES OF THE CRABS ACANTHOCYCLUS UNDER INTERTIDAL MUSSEL BEDS - THEIR EFFECTS ON THE USE OF PRIMARY SUBSTRATUM
    (1989) CASTILLA, JC; LUXORO, C; NAVARRETE, SA
    The mid rocky intertidal of Cachagua, like many other rocky sites in central Chile, is dominated by beds of the mussel Perumytilus purpuratus. Under these mussel beds the predatory crabs Acanthocyclus gayi and A. hassleri build separated bind-ending galleries whose floor is the rock and the roof is the mussel bed. Samples of 1 m2 of Perumytilus beds (100% cover) showed that the surface area of crab galleries ranged between 17.4% and 34.7% of the total area, and that 80% of the crabs were A. hassleri. In 130 of the 157 galleries analyzed, one or two conspecific crabs were found. In the remainder, up to six crabs were found together. Comparisons between the floor of crab galleries and similar rocky areas under the mussel bed, but without galleries (controls), showed that both density and cover of Balanus flosculus, Phymactis clematis and bryozoans were significantly higher in galleries. Similarly, the total number of species was greater on the floor of the galleries than in the controls. Although from outward appearances the cover of P. purpuratus remained at 100%, crab galleries allowed more sessile species to occupy the mid intertidal fringe. This occurs because of the introduction of species typical of the lower intertidal, which would otherwise be excluded by mussels.