Annelida (Oligochaeta and Aphanoneura) from the Natural Reserve of Isla Martín García (upper Río de la Plata estuary, Argentina): biodiversity and response to environmental variables.

Ii César

doi:10.1590/1519-6984.21412

Abstract

The Island of Martín García--located in the Upper Río de la Plata, to the south of the Uruguay River--is an outcropping of the crystalline basement. Fourteen sampling sites were selected, five along the littoral section of the island and nine in inland ponds. Four major environmental variables were measured: water temperature, dissolved oxygen, electrical conductivity, and pH. A total of 34 species of Oligochaeta and Aphanoneura were found, 30 belonging to Naididae plus one species each of the Narapidae, Lumbricidae, Enchytraeidae, and Aeolosomatidae. The thirteen most frequent species were: A. leydigi (30%), N. bonettoi (13%), L. hoffmeisteri (11%), N. variabilis (10%), S. trivandrana (6.5%), A. pigueti (5.6%), D. sawayai (4.5%), D. digitata (3.5%), C. diastrophus (2.7%), A. costatus (2.5%), P. longiseta (2.0%), Enchytraeidae (1.5%), and A. p. paraguayensis (1.4%). UPGMA clustering of species based on their occurrence in different ecological conditions revealed two main species groups. Canonic-correspondence analysis (CCA) was conducted with the 15 most frequent and abundant species in the 9 sampling sites and the 4 environmental variables. Results from the CCA revealed that the order of fluctuation of the environmental variables during the sampling period was, from the greatest to the least: dissolved oxygen, conductivity, pH, and water temperature. Approximately 97.6% of the correlations between species and environmental variables were expressed on axis 1 of the ordination diagram. Species richness correlated with the four environmental variables in the following order, from the weakest to the strongest: water temperature, pH, electrical conductivity, and dissolved oxygen.

Highlights

The annelid class Oligochaeta – considered by many authors as a bioindicator of environmental conditions – is represented by a large number of genera and species present in continental waters within the benthic, pleuston, and periphyton communities (Hellawell, 1986; Rosenberg and Resh, 1993)
Results from the correspondence analysis (CCA) revealed that the order of fluctuation of the environmental variables during the sampling period was, from the greatest to the least: dissolved oxygen, conductivity, pH, and water temperature
The second consisted of several subgroups, where the group Limnodrilus udekemianus Claparede, 1862 and S. trivandrana and the one composed of the Aelosomatidae, Enchitraeidae, L. hoffmeisteri, and A. leydigi became included in the maximum-similarity index

Summary

Introduction

The annelid class Oligochaeta – considered by many authors as a bioindicator of environmental conditions – is represented by a large number of genera and species present in continental waters within the benthic, pleuston, and periphyton communities (Hellawell, 1986; Rosenberg and Resh, 1993). Because of the island’s status, several investigations have been conducted on the flora and fauna of the island focusing on their biodiversity and ecology. Those studies mostly dealt with hydrophilic plants (Lahitte and Hurrell, 1996), vertebrates (Juárez, 1995; Lahitte et al, 1995; Lahitte and Hurrell, 1998), and aquatic and semiaquatic Insecta (Fernández and López Ruf, 1999)

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