Reaction of Glossoscolecidae ( Annelida , Oligochaeta ) to flooding in a Central Amazonian inundation forest

Horizontal migration in response to flooding is re­ ported for Glossoscolecidae of a black-water inundation forest. During increasing water-level, Glossoscolecidae migrate towards the dry-land forest, 16-26m distance beyond the water margin. With decreasing water-level, they return to the inundation-forest, following the water margin at 5-1 Om distance. Distribution seems to be cor­ related with humidity and pH of the soil.


INTRODUCTION
In 1976/77, a 'minimal program for ecosys tem analyses' was carried out in a black-water inundation forest (= Igapo) at Rio Taruma Mirim near Manaus, Brazil (Adis. 1977(Adis. . 1981) ) During the non-flooded period (September  (10.7.81, 18.8.81)or 1 m from the water margin up to 31 m distance (27.8.81, 19.10.81, 6.4.82).A split corer (= steel cylinder with lateral hinges) served as collecting device.II was driven into the soil by a mallet.To avoid material decomposition.Glossoscolecidae were hand sorted from the samples in the laboratory and preserved in alcohol on the day of col lection.

RESULTS
During high water-level, Glossoscolecidae-   were collected in the central part of the forest, mostly 16-26 m distant from the water margin (Fig. 3).Some of them apparently mount tree trunks.They were caught in srboreai photo-eclectors (Adis 1981).Others were drowned and mostly eaten by fish when rppearing in the water after having emerged from the humus layer.

ACKNOWLEDGMENTS
Norman Penny (INPA) kindly reviewed the manuscript.Barry Katz (Univ. of North Carolina) helped to identify the stomach contents.
We heartily thank Nildon Pinto Ataide and Edilson de Araujo Silva (INPA) for their help received during field excursions and material sorting.
investigations have now been carried out during rising and re ceding water-level in 1981/82.STUDY AREA, METHODS The study area is situated at the lower course of Rio Taruma Mirim, an affluent of the Rio Negro about 20 km upstream from Ma naus.A detailed description of the area investigated is given in Adis (1981).Soil samples were taken in the upper, central and lower part of the Igapo: -1) During the receding flood stage at site U (Fig. 1) on July 10, 1981, at site L, on August 18.1982 and 100 m south of site L a on August 27.1981; -2) During the increasing flood stage between sites L, and U on April 06.1982.Additional soil samples were taken near the forest edge (150 m west of site L a ) on October 19, 1981.At each site, five soil samples 21 cm, depth 10 cm) were col lected every 5 m along a transect towards the dry-land forest Samples were either taken from the water margin up to 20 m distance were found concentrating between 5 m and 10 m distant from the water margin in the upper part of the forest (Fig. 2: L D ) .Up to 45 specimens per sample (= about 1300 m 2 ) were collected in July 1981.the majority from the 6-10 cm deep humus layer (= matting of roots with fine humus) .With increasing distance from the water margin, soil humidity and pH decreased (Fig. 2: U) and the number of Glossoscolecidae sampled dropped signifi cantly (p<0.05).Only a few specimens were encountered when soil humidity was lower than 30'/f and soil pH below 3,6.With receding flood, Glossoscolecidae immi grated into the Igapo, in accompanying th3 humid places in the forest ( 1 ) -Max-Planck-Institute for Limnology (Working Group: Tropical Ecology), D-232 Plön, West Germany, in coopera tion with Instituto Nacional de Pesquisas da Amazonia, Manaus.(e.g.logs, roots of buttressed trees, soil depressions), where they stayed until the end of the dry season in December (comp.Adis 1981, 1982) .The maximum number of Glossoscolecidae collected in the lower part of the forest in August 1981 was 22 specimens per sample (= about 635, m 2 ).Most of them were found between 1 m and 11 m distant from the water margin (Figs. 2, 3).Throughout the horizontal immigration into the Igapo, single cocoons were deposited in the humus layer.The receding high water-level-reached the forest edge in October 1981, where no Glossoscolecidae could be found in soil samples.During the rainy season of the non-flooded pericd (December -March, April), Glossoscolecidae were colonizing the humus layer of the inundation forest.Gut contents, examined throughout the period investigated, mainly contained small roots (calyptras), small leaves (litter), tannins, few hyphae and spores of fungi and almost no soil particles (comp.Schaller 1973) .In the anterior part of the digestive tract elongate-shaped bacteria ("bacilli") were found; in the posterior part roundshaped bacteria ("cocci") occured (Katz, pers comm.).

Fig. 3 -
Fig. 3 -Total catch of Glossoscolecidae (in %) sampled up to 26m distance from the water margin during receding flood stage in the lower part of the forest (27.8.1981) and during increasing flood stage in the central part of the forest (6.4.82; 5 samples taken every 5m).