Cladoceran assemblages in a mineralization gradient

Cladoceran assemblages were studied in littoral samples from 44 water bodie s in Central Spain, showing great differences in salinity and permanence of water. Principal component analyses (PCA) were performed with data on clad oceran relative abundances to identify the main groups of species. Five mai n groups of species were found, defining the following types of environment s: (I) Small but deep hard water lakes (II) permanent but shallow hard wate r lakes fed by surface springs, rich in macrophytes (III) ephemeral and sha llow soft waters lakes (IV) subsaline and hyposaline lakes in their lower r ange, specially the permanent ones and (V) saline lakes (salinities >6 mg l (-1)) subject to short or long periods of dryness. The main species constit uting these groups were: Group (I): Acroperus neglectus, Alona guttata, Ple uroxus truncatus, Daphnia longispina; group II: Phrixura leei, Latonura rec tirostris, Eurycercus lamellatus; Alonella excisa, Daphnia pulicaria; group III: Ephemeroporus phintonicus, Macrothrix rosea, Moina micrura; group IV: Alona rectangula, Ceriodaphnia reticulata, Tetrocephala ambigua, Diaphanos oma mongolianum; group V: Alona salina, Pleuroxus letourneuxi, Dunhevedia c rassa, Moina brachiata, Daphnia magna and Daphnia mediterranea. Sample scor es from PCA extracted from the correlation matrix of cladoceran proportions were correlated with limnological measurements. Significant correlations w ith salinity, alkalinity anions and cations indicate that salinity is an im portant factor in the distribution of the species. However, species assembl ages also reflect other factors, such as temporality and littoral developme nt.