Cambios interanuales en la biomasa y biodiversidad de zooplancton gelatinoso en aguas interiores de Chiloé, sur de Chile (primaveras 2004 y 2005)

zooplankton biomass was compared between the fraction of chitinous and gelatinous organisms from the southern region of chile between puerto montt and boca del guafo, in the springs of 2004 and 2005. the biomass values were higher in 2004, being mainly composed by chitinous fraction, particularly in the north microbasin. conversely, during 2005, a sharp increase of the gelatinous fraction was observed reaching 60% of the total biomass in the northern microbasin, and gradually decreasing into the boca del guafo. the increase in biomass seemed to be a result of the explosive proliferation of the siphonophore muggiaea atlantica, whose densities increased 5.6 folds in 2005, triggering a drastic decrease in diversity of the gelatinous zooplankters. in both springs, 34 species of semi- and gelatinous organisms were identified, distributed in six chaetognaths, six siphonophores and 22 hydromedusae. chaetognaths and siphonophores had previously been registered for the study area, but all hydromedusae encompass new records for the area between puerto montt and boca del guafo.