Soil Organisms (Apr 2021)
The abundance and diversity of Enchytraeidae and Naididae (Oligochaeta) in Amazonian forest ecosystems at different stages of human impact
Abstract
Enchytraeidae are known to be an important group of soil animals in temperate regions of the world but their diversity as well as their contribution to soil functions, esp. litter decomposition, in the humid tropics remain largely unexplored. Therefore, as part of the SHIFT (‘Studies of Human Impact on Floodplains and Forests in the Tropics’) project ENV 52, entitled ‘Soil Fauna and Litter Decomposition’, their species composition, abundance and biomass were determined in an experimental agroforestry area located about 20 km north of Manaus (Amazonia), Brazil, between 1997 and 2000, focusing on four plots with differing degree of human impact. In addition, individuals of the family Naididae were sampled at these plots as well. The aim of the project was to study the regeneration and anthropogenic usage of degraded forest areas, to mitigate the human impact on primary rain forests in Amazonia. Study sites were two polyculture tree plantations (POA, POC) and two plots of nearby secondary (growing since 1984, SEC) and undisturbed primary forest (FLO). Samples for both Enchytraeidae and Naididae were taken quarterly for two years and the worms were extracted by wet extraction (120 samples, each divided into litter and soil layer) per sampling date. The enchytraeids were identified in vivo, whereas naidids were initially only counted. Later on, and after fixation in EtOH, selected specimens were identified. Identification of the worms followed a site-specific key, based on information from the literature and own experience. The biomass of larger enchytraeids (i.e., the genus Guaranidrilus) was determined via weighing, while the biomass of smaller enchytraeids was estimated by using values previously determined for European species of similar size. In total, 18 enchytraeid and 14 naidid species were found. Most of the former belonged to the mainly neotropical genus Guaranidrilus (5) and to the cosmopolitan genus Hemienchytraeus (5). Species of genera typical for temperate regions, such as Achaeta spp. (4) and Enchytraeus spp. (2) were also found. The abundance of enchytraeids found in the primary forest (1,000–10,000 Ind/m²) was comparable to those found at other tropical rain forest sites. The abundance in all four plots was similar, whereas the biomass was lower in POA and POC than in FLO and SEC. However, variability between replicates was high. No annual phenology pattern was observed, but dry conditions in 1997 had a negative influence on enchytraeids. The four plots were similar concerning species number and composition, but dominance patterns differed: the dominant genus in FLO was Hemienchytraeus, but Guaranidrilus on all other plots. Naidids seem to regularly occur in terrestrial samples of tropical rain forests; their species number was high in relation to their abundance but most species were new to science. The micro-annelid community indicated a clear distinction between forest (FLO, SEC) and plantation (POA, POC) sites.
Keywords
