Estudio cuantitativo y estacional de dos poblaciones de cnidarios plactónicos frente a las costas de Barcelona (Mediterráneo Occidental): ciclos entre 1966-67 y 1982-83

Resum

A quantitative and seasonal study of two populations ofplanktonic cnidaria off the coast of Barcelona (Western Mediterranean): Comparison between 1966-67 and 1982-83
Two populations of planktonic cnidarians were sampled between November 1966 and December 1967, and between Setember 1982 and August 1983 off the coast of Barcelona. In both penods, samples of zooplankton were taken using similar methodology, from surface water layer. The seasonal and quantitative distnbution was studied. A total of 37 species of cnidar of Muggiaea kochi and Lensia subtilis, while M. atlantica a 90% of the total in the 1982-83 period. Lizzia blondina and Obelia spp. were seasonal dominant in 1966-67 while Aglaura hemistoma characterized the medusa fauna along all 1982-83 period. The total diversity of cnidarian populations was significantly different in 1966-67 and 1982-83: the number of individuals 1100 m3 in 1982-83 was only 30% of the collected individuals dunng the 1966-67 period. The decrease of local cnidarian fauna is discussed but the effective cause is still ignored.