Barbara Robertson

Vertical distribution of zooplankton and physico-chemical conditions during a 24-hour period in an amazon floodplain lake-lago calado, brazil

In May 1980 Lago Calado was 9 meters deep, the water level was rising slowly, and below 4 meters the water was anoxic. Virtually all of the zooplankton was in the oxygenated layer. Adult and juvenile Daphnia gessneri, the most abundant crustacean species, occurred between 0.5 and 4.5 meters. Copepod nauplii tended to occur nearer to the surface, in the 0—2 meter stratum. No clear vertical migration was observed. The epilimnion was undersaturated ( 2 μ M) and ammonium ( > 5 μ M), but little nitrate ( < 0.1 μ. M). A peak in particulate carbon and nitrogen occurred between 4-5 meters, just below the thermocline, and was associated with a pigment maximum.

Atlas de copépodos planctônicos, Calanoida e Cyclopoida (Crustacea), da Amazônia Brasileira: I. Represa de Curuá-Una, Pará

This paper was elaborated with intention of complementing original descriptions, updating the distribution ofthe species and providing the taxonomic basis necessary for a secure identification of the animals. We present detailed ilustrations of 6 species of Calanoid copepods and 3 species of Cyclopoids copepods found, but not necessarilly restricted to the Curua - Una Reservoir located in the municipality of Santarem, state of Para, Brazil.

Composição do Zooplâncton em diferentes ambientes do lago Camaleão, na ilha da Marchantaria, Amazonas, Brasil

This study aims to verify occurrence and distribution of the major zooplankton groups in three different sub-habitats at Lago Camaleao: channel, aquatic macrophytes and flooded forest, during the high water period (August, 1996). Cladocera, Copepoda and Rotifera occurred with different relative abundances within the three studied environments. In the channel, Cladocera occurred with a high number of species and individuals, Bosminopsis deitersi being the dominant species (89%). Cladocera and Copepoda were equally dominant in the flooded forest, even thought only copepods, nauplius and copepodites immature forms were found. On the macrophytes, Rotifera was the group with the largest occurrence, with the dominance of Lecane quadridentata, Keratella Americana and Brachionus patulus followed by copepods (immature forms) and cladoceres, the latter mostly of the Chydoridae family (21.4%).

A new species of Notodiaptomus Kiefer, 1936 (Copepoda, Diaptomidae) from the Amazon and Orinoco River Basins

A new species of Notodiaptomus, Notodiaptomus simillimus sp. nov., based on the female originally but erroneously assigned to Rhacodiaptomus calatus, and the corresponding newly discovered male, is described and illustrated in detail. The designation of the female as a new species of Notodiaptomus, and the recognition of the corresponding new male, is based on detailed morphological and biometrical studies, analysis of the known distribution and material from laboratory cultures. Morphological analysis demonstrated that the female shares the form of the external genital area and setal armature of the exopod 2 of leg 5 with other species of Notodiaptomus but they differ from those exhibited by species of Rhacodiaptomus. The distributions of the female and male assigned to Notodiaptomus simillimus sp. nov. overlap and include the Atabapo and Guaviare Rivers and Lago Calado. On the other hand, the distributions of the males and females originally assigned to R. calatus are disjunct and where they overlap, that is, in Lago Calado, each is accompanied by its respective mate. Laboratory cultures showed that, as expected, copulation did not occur between males and females described originally as R. calatus. This experiment demonstrated the existence of reproductive isolating mechanisms between these females and males, and confirmed the existence of two distinct genetic pools, i.e. two different species, the original males being of the valid R. calatus and the female a new Notodiaptomus. This female and the corresponding newly discovered male are N. simillimus. The new species is closely related to N. coniferoides.

A NEW SPECIES OF Rhacodiaptomus Kiefer, 1936, FROM THE BRAZILIAN AMAZON (CRUSTACEA:COPEPODA: CALANOIDA)

A new species of Calanoid copepod, Rhacodiaptomus besti,is described from material collected in the Igarape Sao Pedro, Rio Jamari, State of Rondonia, and Lago Amana, Rio Japura, State of Amazonas, in Western Amazonia. A detailed morphological analysis of the species was undertaken in order to provide a basis for future studies on inter and intrageneric relationships.