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vol.30 número1  suppl.SympEffects of "El Niño" Events on the Sublittoral Macroinfauna in Bahía Iquique, ChileImpacts of El Niño/La Niña on the Population Dynamics of the Tropical Bivalve Donax dentifer from Bahía Málaga, Colombian Pacific índice de autoresíndice de materiabúsqueda de artículos
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Investigaciones marinas

versión On-line ISSN 0717-7178

Investig. mar. v.30 n.1 supl.Symp Valparaíso ago. 2002 

Diversity of the Sublittoral
Macroinfauna in Bahía Iquique during
and after the 1997-98 "El Niño" Event

Rodrigo Moreno M.1,
Roger Sepúlveda S.1,3,
Franklin Carrasco V.2

1Departamento de Zoología, 2Departamento de
Oceanografía, Facultad de Ciencias Naturales y
Oceanográficas, Universidad de Concepción Casilla
160-C, Correo 3, Concepción, Chile,
3Depto. Ecología Costera, Facultad de Ciencias,
Univ. Católica de la Ssma. Concepción.

The aim of the present study was to study the dynamics of the community structure of benthic sublittoral macroinfauna associated with the soft bottoms of Bahía Iquique (20º 10' S, 70º 09' W) during and after the EN97/98 event. Alpha and beta diversities were evaluated, comparing the relation between the components of the diversity and the size of the samples.

The major relative abundances during and after the EN97/98 event were the polychaete Paraprionospio pinnata (33.91% and 37.12%) and the gastropod mollusc Nassarius gayi (10.69% and 16.96%) These were considered dominant species during and after the event, and were followed in abundance by the polychaete Haploscoloplos kerguelensis chilensis as a dominant species after EN97/98 with 5.04% of the total.

The most frequent species in the samples were the polychaetes H. kerguelensis chilensis, P. pinnata and the gastropod N. gayi, with frequencies of 66.67%, 62.5% and 58.33% respectively during EN97/98. After the event, except for P. pinnata (81.48%) and N. gayi (59.26%) the frequencies remained constant. Furthermore, the polychaetes Diopatra oblique (55.56%), Nephtys ferruginea and Aricidea pigmentata (51.85%) were additionally found to be frequent species.

The similarity between populations during and after the EN97/98 amounted to 58.6% with 41 species remaining after the event, and 18 species lost, which could be explained by hydrographic changes or as an artifact derived from the sampling methodology.

The components of diversity were directly related to the size of the samples, thus the richness (during EN97/98: R2=0.991 n=24; after EN97/98: R2=0.9781 n=27) followed a function of potential type; in contrast, the component of abundance (during EN97/98: R2=0.9682 n=24; after EN97/98: R2=0.9778; n=27) followed a linear function. Both relationships were significant for both periods (ANCOVA, F(1,48)=22.56; p<0.01 for the relation of species and ANCOVA F(1,48)=14.08; p<0.01 for the relation of individuals). The test for parallelism found significant differences between gradients in the relation of richness (F(1.47)=14.88; p<0.01) but not for the relation of abundance (F(1.47)=2.53; p>0.11).

Cluster analysis showed that the association between stations did not correspond to the factorial abiotic similarity that affects the bay, since the grouping between stations during and after "El Niño" is based mainly on the similarity in the specific composition between stations. Instead, it corresponds to a condition of community organization based on the presence of species that are more resistant to environmental changes, such as temperature and bottom oxygen levels. On the other hand, multidimensional scaling analysis revealed a pattern of grouping for each period, where the stations sampled during the EN97/98 period were grouped independently from those sampled after the EN97/98 event. This pattern suggests a change in the community, based mainly on the presence or absence of rare and common species that were present in each period, so that the presence of rare species would shape and significantly determine the local alpha diversity. Conversely, the presence of common species would generate the structure of basal dominance of the communities in both periods.

The species diversity during EN97/98 was 4.171, with an evenness of 0.709 which accounts for species that dominate in the bay with abundances that did not exceed 32%. In the period after EN97/98 the diversity and evenness decreased (3.519 and 0.617 respectively), suggesting an increase in abundance of the more dominant species maintaining the community structure of the stations.

The mean diversities of the stations sampled during EN97/98 showed a tendency to major diversities in the most central stations (E4, E5 and E6) and minimal diversities in the extremes (E1 and E8). In the period after EN97/98 the bigger mean diversities remained in the central zone (seasons E3, E4 and E5) and the minor diversities remained in the most external and internal zones of the bay (E1, E2, E7 and E9).

The changes of structure in the communities, associated with high ecological dominances of some species, allow us to conclude that the temporal changes of the benthic macroinfauna of Bahía Iquique are caused by an event that is able to regulate and modify the spatial structure and dynamics of the benthic communities associated with the abiotic effects of the EN97/98 event.

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