Portal de Periódicos da CAPES

Las comunidades de macroinvertebrados a lo largo del río Llobregat

1984; Volume: 1; Issue: 1 Linguagem: Inglês

10.23818/limn.01.29

2660-8537

Xavier Millet,

Mollusks and Parasites Studies

The macroinvertebrate species of the Llobregat river were studied at three different year periods (August 1979(August ,december 1979(August and april 1980)).The relative abundances of species at 18 sampling sites were used to perfom some comparisons.The sampling sites similarity indexes and the species distances were calculated and hierarchicaly clustered for each of the sampling seasons.A multivariate analysis was also carried out including al1 the information avalaible.The cluster analysis for the sampling sites yield the expected spring versus mouth organization, except for some neighbourg permutations.T h e unique and clear alteration in the sites succesive ordination was the station 2 in winter due to a pollution effect observed a t this station in that period.Anyway, the general grouping in al1 the seasons can be summarised as follows: An upper group of sampling stations with low similarities, a medium group with the highest similarities (dueto the presenceof a reduced number of abundant species), and finally, the sites in the lower reaches.At the upper reaches the benthic fauna is diverse and composed by riverine species, in the central reaches the uniformization in macroinvertebrate fauna is produced by a moderate pollution and the scarcity of the fauna in lower sites is a result of the very high pollution.Based on field observations and on the sorting experience, six groups of species were stablished in a cluster analysis.The results of species clustering yield some of the groups constant for the three different seasons.These correspond to the spring species, the central reaches species (inhabiting the central uniform zone) and the pollution resistent species (inhabiting the lower part of the river).Other groups are composed either by non significant species (mainly present in the tributaries) or species present in the upper reaches where the community s t m m r e is much more complex.In the ~r i n c i p a l component analysis (PCA) the three first factors (accounting for 15'5%, 10'5% and 8% of the were analized.The first factor is loaded by the abundant species in central reaches and the third one is 10aded bv the indicator species on any group.A~cording with this results we believe that neither a continous model can be stated in the community structure along the river channel nor a discrete one.Although some continous structure is notice in the upper reaches, in the central and lower part and also in spring zone defined communities can be distinguised.But these defined groups of species are produced either by disturbance introduced by man as pollution (in central and lower reaches) or by a great constancy in some abiotic factors (as temperature in the spring zone).