Revista Chilena de Historia Natural 78 (1): 33-50, 2005
RESEARCH ARTICLE
Population biology of the subtidal kelps Macrocystis integrifolia and
Lessonia trabeculata (Laminariales, Phaeophyceae) in an upwelling ecosystem of northern Chile:
interannual variability and El Niño 1997-1998
This paper describes the population biology of Lessonia trabeculata and
Macrocystis integrifolia during and after the 1997-1998 El Niño in an area of permanent coastal upwelling in northern Chile.
Spatial and temporal patterns of distribution were evaluated seasonally for adult and juvenile sporophytes of both species between
1996 and 2003. These two kelp form an assemblage distributed between 2 and 15 m depth, with disjunct patterns along a bathymetric
gradient, including two morphs of L. trabeculata, the occurrence of which depends on the presence or absence of
M. integrifolia. During the 1997-1998 El Niño the spatial-temporal patterns of abundance of the kelp assemblage were
maintained by the continuity of coastal upwelling, which buffered and moderated superficial warming of the sea and depletion of
nutrients. In this context, localities associated with coastal upwelling areas could function as “sources” of reproductive propagules after
passage of El Niño, thus increasing kelp recolonization rates in “sink” localities, which suffered local kelp extinctions. Intensification of
upwelling processes after the 1998-2000 La Niña increased nutrient inputs into subtidal habitats, favoring the productivity of the kelp
assemblage. However, an abrupt change in the spatial-temporal patterns of abundance of the black sea urchin Tetrapygus
niger, the most conspicuous benthic grazer in northern Chile, produced local extinctions of M. integrifolia and
compression of the range of bathymetric distribution of L. trabeculata. Top-down (mortality of benthic carnivores during the
1997-1998 El Niño) and bottom-up effects (intensity and frequency of upwelling) in this subtidal coastal ecosystem appear to regulate
the kelp-herbivore interactions in the study area. The main sources of reproductive propagules for the reestablishment of the
assemblage kelp were fertile sporophytes which included isolated, low density patches of M.integrifolia located within the
bed of L. trabeculata, although drifting kelp rafts and “seed banks” of microscopic dormant stages may provide
supplementary recruitment. In the temperate SE Pacific, oceanographic events that act on different spatial-temporal scales plus low
frequency biological processes (changes in grazer abundance), which act on local scales, produce inter-annual variability in the long
term dymanics of kelp populations. Furthermore, the interactive effects between centers of permanent upwelling and the oscillating
temporal periodicity of oceanographic events that produce positive (El Niño) and negative (La Niña) thermal anomalies modify the
spatial arrangement of subtidal kelp populations on a latitudinal gradient.
Key words:
subtidal habitats,
population and community ecology, extinction and re-colonization processes, kelp-herbivore interaction, El Niño, La
Niña
