Assemblage of Benthic Macroinvertebrates in Soft Bottoms of the RIÍTO ARM, Rancheria River Deltaic System

Benthic macroinvertebrates associated with soft bottoms are a key element in the balance of aquatic ecosystems, as they play an important role in ecological processes, such as nutrient cycling, dispersal and particle capture, among others. For this reason, the objective of this work was to analyze the assembly of benthic macroinvertebrates associated with soft bottoms in the Riíto arm of the estuarine deltaic system of the Ranchería River, in the department of La Guajira (Colombia). This system has been shown to be highly changeable in previous studies, so it is necessary to carry out environmental monitoring. During the period from September 2022 to January 2023, temperature, pH, conductivity, transparency, depth, alkalinity and hardness of the water were measured in situ, as well as sediment samples were taken to determine its granulometry and organic matter, and to analyse benthic macroinvertebrates, at three sampling sites: Desembocadura (DB), Mirador (EM) and Villa Fátima (VF) along the El Riíto arm in the Rancheria River delta. Two species were found: Pyrgophorus platyrachis and Mytilopsis leucophaeta. The density of organisms was higher in MS, with 62.5 individuals per square meter, although the sampling sites presented only a slight separation according to their physicochemical characteristics, mainly due to the variability of oxygen saturation and mean sand. Only fine sand was associated with the density of P. platyrachis as the dominant species of the El Riíto arm (87.1 % of the total abundance). It is concluded that, according to the composition and abundance of organisms, DB and VF are different from EM, since the latter site showed the highest densities of organisms, which indicated slightly more favorable conditions for them. Likewise, it was evidenced that the physicochemical variability within the estuary is mainly temporary.