Dinâmica populacional e hábitos alimentares em Macrobrachium sob influência de barragem

Abstract

The aquatic organisms’ ecology study is essential to evaluate the impacts of dams and to support conservation and maintenance measures of biological diversity in these locations. The prawns Macrobrachium amazonicum and Macrobrachium brasiliense, important links in the food chain of aquatic environments, were evaluated for population dynamics and food habits to infer possible impacts caused by the removal of the dam in area of study. The crustaceans were collected upstream and downstream of the Rio Pandeiros dam, using a sieve with 1 mm mesh size, in the dry seasons and rainy, between July / 2014 and Feb / 2015. For analysis of the population dynamics, the animals were sexed, and the total length (TL) and carapace length (CL) were measured, grouped into size classes, the eggs and the ovigerous females counted and weighed. To evaluate the influence of environmental factors was used analysis of hierarchical partition. In the study of feeding habit, the prawns had their stomachs removed and observed the degree of fullness, frequency of occurrence and the relative frequency of each item. A total 414 specimens of M. brasiliense and eight M. amazonicum (just downstream) was collected. Upstream the abundance was lower, only 15 individuals. Males were more representative in the population of M. brasiliense, and females in M. amazonicum. The factor that best explained the abundance on downstream was temperature. The higher ratio demonstrated by multiple regression analysis was between the CL of the females and the average volume of eggs. A total 324 stomachs of M. brasiliense and eight M. amazonicum was analyzed. Downstream there were more items in the stomachs. The main items were: vegetable detritus, algae, digested material and insects, suggesting omnivorous behavior for the species. Through the comparison of the abundance and of frequency of food items observed to both prawns, it can be concluded that the dam may be affecting the populations of prawns, reducing macrophytes richness and abundance of prawns and reducing organisms that serve as food for them. Macrophytes are shelters for various aquatic invertebrates. Furthermore, upstream is the most affected region, because the dam turns the place into more homogeneous environment.