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The purpose of this study was to analyze changes in the assemblage of benthic macroinvertebrates, as a response to anthropogenic environmental alterations in a river of the Extra-Andean Patagonia. Four sampling surveys were carried out between March 2017 and March 2019, in contrasting seasons on the middle course of the Chico River (Santa Cruz). Six sampling stations were established: two reference stations upstream of Gobernador Gregores town and four downstream at increasing distances from the locality. At each station, physic-chemical variables were measured and four macrobenthos samples were collected using a manual Surber-type net with a 500-µm mesh. The abundance of taxa and functional feeding groups (GFA) were analyzed using univariate and multivariate statistical methods. Twenty-six taxa were identified; the best represented were oligochaetes, hirudineans, gastropods and Chironomidae, Baetidae and Glossosomatidae insects. The reference stations and those further from the town presented higher values of diversity and richness of taxa and GFA; Chilinidae and Lymnaeidae molluscs were more important together with Baetidae, Glossosomatidae and Gripopterygidae insects. At the downstream stations, closer to the town, Naididae oligochaetes and Chironomidae insects dominated the macroinvertebrate assemblage with lower values of diversity and richness of taxa and GFA. The collectors-gatherers were the dominant feeding groups in these stations, where the contribution of urban effluents favored the detrituseating pathway and the opportunistic feeding strategy. Changes in composition and trophic structure of the macroinvertebrate assemblage provide relevant information to understand ecological modifications due to environmental alteration, and are of fundamental importance to interpret the biotic indices used to evaluate water body quality. [ABSTRACT FROM AUTHOR]

In this study, we analyzed the relation between the abundance of benthic macroinvertebrates and relevant environmental variables in two intertidal in Golfo Nuevo (Argentinean patagonia), one near a urban center (Mimosa Beach, PM) and the other at 20 km from that location (Cerro Avanzado Beach, CA). Within each beach, the environmental conditions were homogeneous (90% of similarity). Mean size grain values, anoxic layer depth, and percent organic matter were 117.6 µm, 4.95 cm and 0.76%, and 165.2 µm, 9.5 cm and 0.63%, for PM and CA respectively. Even though three families were the most abundant in both beaches (Tellinidae, Maldanidae and Opheliidae), nine families were exclusively observed in PM. This resulted in a higher biodiversity in PM (3.06) in relation to CA (1.77). When faunal composition was considered, the similarity between sites was notably low (lower than 82%) if compared with the environmental conditions. Granulometry and organic matter were the variables with the highest correlation with macroinvertebrates abundance. This is the first study of macroinvertebrates and their relationship with some environmental variables throughout the complete spatial extension of two beaches in Golfo Nuevo. This is of particular relevance if we consider that coastal regions of this gulf has been exposed to a sustained increase of anthropic activities in the last years and base- line information is scarce. [ABSTRACT FROM AUTHOR]

This paper documents the disturbances suffered in 1994 by the coral communities of Braithwaite, Vargas Lozano and Binners bays of southern Socotro Island, Revillagigedo Archipelago (18 deg. N), after an event of excessive sedimentation caused by an input of terrigenous sediments from the island surface. This phenomenon probably occurred because of the severe erosion of the southern zone of Socorro, originated by the overgrazing and transit of the population of feral sheep (Oviscries L.), whose activities have caused severe soil losses in the locality. The sediment primarily damaged the coral colonies at Braithwaite Bay, and conspicuously diminished the rocky areas suitable for use by other marine invertebrates. The noticeable differences in the development of coral communities from northern and southern Socorro Island may be due to the repeated occurrence of similar events in the past, as the sheep have lived on the island for more than one century. This paper presents the first record of sedimentation damages to marine communities in oceanic islands of the Mexican Pacific. [ABSTRACT FROM AUTHOR]