The distribution of scaled chrysophytes in the delta region of the Parana River, Argentina

A total of 33 taxa of scaled chrysophytes were observed from 50 localities in and around the delta region of the Parana River, situated in the subtropics of Argentina. The study sites were divided into five groups based on their physical and chemical characteristics and location within the delta complex. The five groups included waterbodies situated on the delta, channels of the river, tributaries draining mostly urban areas, tributaries draining farm or ranching areas, and streams draining areas with exposed limestome. The pH and specific conductivity of the localities ranged from 6.0 to 9.1 and 123 to 3,750 fJ.S cm-', respectively. Species diversity and abundance clearly decreased with increasing pH and specific conductivity. The majority of species were found in the more dilute waterbodies located on the delta, while few taxa were observed within the river proper or the tributaries draining agricultural or urban lands. The flora contained species that are cosmopolitan, temperate, as well as tropical in nature. In particular, species reported to be common in the tropics and observed in this study included M. matvienkoae var. grandis, M. guttata, M. peronoides var. peronoides, M. peronoides var. bangladeshica, M. portae-jerreae, M. mangojera var. reticulata and Synura australiensis. Mallomonas caudata and M. crassisquama, often reported as the most abundant species of scaled chrysophytes in other regions of the world, were rare and absent, respectively, in the delta region.