Browsing by Author "CAMUS, PA"

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    RECRUITMENT OF THE INTERTIDAL KELP LESSONIA-NIGRESCENS BORY IN NORTHERN CHILE - SUCCESSIONAL CONSTRAINTS AND OPPORTUNITIES
    (1994) CAMUS, PA
    The strong 1982/83 El Nino event caused local extinction in populations of the low intertidal kelp Lessonia nigrescens Bory on northern Chilean coasts. The kelp has partially recolonized, but its recovery has apparently been low. This study documents the effect of biological factors that potentially decrease the velocity of kelp recolonization in northern Chile. A removal experiment showed that encrusting coralline algae, which dominate the lower intertidal, significantly reduce the recruitment of L. nigrescens in the presence of herbivores. Epithallium shedding by encrusting corallines is the most probable cause for this inhibition process. On the other hand, grazing on encrusting corallines by the chiton Enoplochiton niger (Barnes), a large-sized herbivore (10-20 cm length), could also affect kelp recruitment. The intestinal content of E. niger, where encrusting corallines are the main item (84.2%), revealed the presence of L. nigrescens. Among the natural substrata on which kelp recruits, measured at five different localities, the coarsely-branched alga Corallina officinalis (Decaisne) Kutzing reached the highest frequency, despite its extremely low cover (< 1%) in the field. This suggests that settlement on turfs of C. officinalis allows the kelp to escape from herbivory, thus facilitating its recruitment. The roles of timing of kelp recruitment and seasonal grazing are also discussed.
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    SCALE-DEPENDENT VARIABILITY OF DENSITY ESTIMATES AND MORPHOMETRIC RELATIONSHIPS IN SUBTIDAL STANDS OF THE KELP LESSONIA-TRABECULATA IN NORTHERN AND CENTRAL CHILE
    (1992) CAMUS, PA; OJEDA, FP
    Several morphological parameters, and estimates of density and evenness per depth, were analyzed for stands of the subtidal kelp Lessonia trabeculata Villouta et Santelices from 2 zones, central and northern Chile. Two sites in each zone were sampled for 2 yr, and variability patterns were statistically described using site or zone as classification factors. Bathymetric profiles of density showed a strong qualitative and quantitative variation among sites, contrasting with the high evenness in spatial distribution of plants per depth interval, despite intervals of varying length. Relationships among morphometric parameters changed markedly across spatial scales, producing a high variance in biomass predictions. In most cases, strong site- and zone-specific components were identified, which account for the variability in morphology at both spatial scales. Zone effects may mirror water motion and temperature regimes, among other factors, and site effects may be related to specific habitat configurations. These results show that extrapolation from structural features of single stands for characterizing species may result in misleading inferences. The detection of scale-dependent patterns proved to be a useful starting point for comparative studies of population structure, and necessary before attempting generalizations.
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    SIZE-SPECIFIC REPRODUCTIVE PARAMETERS IN RED ALGAE - A COMPARATIVE-ANALYSIS FOR 2 SYMPATRIC SPECIES FROM CENTRAL CHILE
    (1992) CAMUS, PA
    Ahnfeltia durvillaei and Gymnogongrus furcellatus, two intertidal red algae from central Chile, often grow sympatrically and their gametophytic phases are dominant in the field, but recruitment is low. A short-term comparative analysis of the reproductive behavior of their gametophytes was carried out to determine quantitative levels of reproduction and their degree of functional similarity. Size, rather than age, was evaluated as predictor of fecundity. Both species showed the same qualitative patterns, although maintaining quantitative differences. Reproductive plants were recorded throughout the size range, and fecundity increased continuously and directly with size. A size-independent threshold in reproductive effort was found for each species, and the variance of effort values decreased inversely with size. Vertical, size-specific life tables revealed low dependence of survivorship with size, and reproductive values exhibited a maximum at the same size class for both species. This last pattern, and a negative relationship found between fecundity and survivorship, suggest the existence of costs or trade-offs operating at the phenotypic level, but they would not be supported in a selective context.
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    THE HUMBOLDT-EL-NINO SCENARIO - COASTAL BENTHIC RESOURCES AND ANTHROPOGENIC INFLUENCES, WITH PARTICULAR REFERENCE TO THE 1982/83 ENSO
    (1992) CASTILLA, JC; CAMUS, PA
    The coastal waters of Peru and Chile are among the most productive of the world's oceans. A striking source of interannual variability in this upwelling ecosystem. El Nino, results in large population and community variations. During El Nino the seasonal upwelling ceases and warm, clear oceanic waters occur close inshore, setting a unique oceanographic scenario in which the performance of populations and communities can be studied. While most attention has been focused on the pelagic components of such systems, numerous changes occur in inshore, benthic populations. Likewise, little attention has been paid to the critical role of humans as predators or active users of inshore, benthic resources. Humans as components of the ecosystem can impose significant alterations on population and community structure. In this paper the fishery statistics of three economically important inshore, benthic resources (the gastropod Concholepas concholepas, the cephalopod Octopus vulgaris and the kelp Lessonia nigrescens) are analysed in relation to the strong 1982/83 El Nino event. In particular, trends are described for landings in the far northern regions of Chile, where the marked effect of El Nino was concurrent with high levels of exploitation of C. concholepas and L. nigrescens.