Taxa de sedimentação e contribuição do banco de formas dormentes (comunidade passiva) para a riqueza de espécies da comunidade zooplanctônica ativa em um pequeno reservatório perene tropical

Abstract

Small reservoirs usually have a great biodiversity and provide several ecossystemic services. Zooplanktonic organisms inhabiting these environments constitute important links in the food chains. Since environmental conditions might fluctuate, these organisms produce dormant forms, which sink to the sediment and guarantee the repopulation of species. Eventhough being crucial for community maintenance, there is a certain lack of information about dormant forms in smaller water bodies in tropical regions, as well as their interactions with the sedimentation process. This study aimed to evaluate the contribution of the dormant forms to the zooplanktonic species richness in the active community, correlating the environmental

variables and the dormant forms bank, in a small dam located in the municipality of Alfenas- MG. Four samplings were carried out in 2019 and the following parameters were assessed:

morphometry; sedimentation rates; physical and chemical aspects of water and sediment and zooplanktonic species richness of the active and passive community. The reservoir was classified as oligotrophic, shallow, with euphotic entire water column besides great diversity of macrophytes. Sixteen taxa were identified in the active community. The samples from the dormant forms bank had between 480 to 5000 eggs/100g of sediment. Hatching rate was low, with only seven taxa identified. From those, two were new to the active community, not found in the water column, thus revealing the relevance of dormant forms bank to maintenance of diversity. Morphometric characteristics and the presence of macrophytes contributed to the species diversity. Albeit being a small of reservoir, sedimentation rates were distinct across time and space, ranging from 0.5 kg to 2 kg per square meter per year. In relation to the sediment granulometry, it was possible to detect that Cladocera were abundant on site with highest fine and coarse sand concentration. Thus, despite many of the morphological characteristics of this reservoir were favorable to species richness, impacts as the introduction of predators suchas fish could be enhanced by its small size and small depth. The eggs bank has, therefore, an important role for the maintenance of the species richness in this site and future efforts to verify the relationships between sedimentation rates and the sediment's granulometry and of this with dormant forms bank should have priority in this type of environments.