Norma Luiza Würdig

Zoogeography of Holocene Podocopina (Ostracoda) from the Brazilian Equatorial shelf

Abstract This study reports on the Holocene ostracods of the Brazilian Equatorial shelf from French Guiana to near Natal, almost 1400 km in length. This part of the Western Atlantic Tropical Province, where the mouths of the Amazon and Para rivers separate two zoogeographical units, has distinct oceanographic and sedimentologic features. Three hundred and thirty nine samples were studied from the REMAC (legs 4, 5, 5A and 6) and the GEOMAR projects (legs I, II and III). The ostracod fauna includes 74 species, of which 37 have been previously described (mostly from other areas). The remaining 37 species are left in open nomenclature although 26 of them are probably new. Twelve species are confined to the northwest and 16 to the southeast of the mouths of the Amazon and Para rivers. The inner shelf of the northwestern region is a barren zone resulting from turbid freshwater discharged by the Amazon and Para rivers. Most of the studied species live at water depths of less than 100 m; 28 species inhabit waters shallower than 75 m, and 18 species live in waters shallower than 50 m. Although Brazilian ostracods have many genera and species in common with Holocene ostracods elsewhere in the tropical Atlantic, diversity differs greatly. For example, diversity on the Brazilian Equatorial shelf is lower than elsewhere in the Western Atlantic Tropical Province, but higher than in the Eastern Atlantic Tropical Province. Faunal similarities between these provinces are at the generic rather than species level; exceptions are few and consist of conservative Tethyan species that are cosmopolitan.

The effects of different rice cultivation systems and ages on resting stages of wetland invertebrates in southern Brazil

The use of machinery and pesticides in modern agriculture are supposed to negatively affect the viability and diversity of invertebrate egg banks. Studies that evaluate the emergence of invertebrates through analysis of their dormant stages are needed in order to identify the resiliency of food webs in wetlands. In this study, the following hypotheses were tested: (1) richness is lower in conventional rice fields than in organic ones and natural wetlands; (2) richness is lower in older rice fields than younger fields; (3) composition varies among different rice systems and ages; and (4) emergence rate may vary among rice systems and ages over time. Dry sediment samples were collected from six rice fields cultivated under different systems, nine conventional rice fields with different cultivation ages and three natural wetlands. Our study showed that the richness was surprisingly higher in conventional rice fields than wetlands, with cladocerans being more associated with the former and insects more frequent in the latter. Invertebrate richness was similar among rice fields of different ages, but the composition differed between 20-year-old fields and younger fields. Variation in the viable resting stages found across different rice cultivation systems and ages contributes valuable information to wetland restoration initiatives.

Effect of Typha domingensis cutting: response of benthic macroinvertebrates and macrophyte regeneration

Wetlands are important because they have high biodiversity and are considered, by environmental agencies, permanently protected areas due to their importance to conservation. In Southern Brazil the aquatic macrophyte Typha domingensis is harvested to be used in the manufacture of handicraft, being an important income source to small farmers. This work aims to test the cut effect of T. domingensis on benthic macroinvertebrates as well as on macrophyte regeneration. These phenomena were analyzed in small areas (1 m2) in a T. domingensis stand by comparing cut treatments and control treatments. Macroinvertebrate were sampled with a corer in the following time sequence after the cut event in both treatments: one day, 26 days, 60 days, 89 days, and 182 days. Macrophyte regeneration was monitored through monthly measurements at each treatment. The macroinvertebrate density did not differ between treatments (ANOVA, p < 0.05). Among the 23 taxa identified, Tubificidae was the only family to response to cut treatment. DCA showed an overlapping between treatments indicating a not clear pattern. The growth of T. domingensis shoots was not affected by the disturbance. Macrophyte regeneration was quick when comparing the treatments and statistical differences were found in one day after the disturbance and 26 days after the disturbance, whereas no differences were found in the remaining sampling dates (60, 89 and 182 days). Observing the macroinvertebrate response and the T. domingensis regeneration, our results suggest that sustainable use of this macrophyte is possible on a small scale.