Realm: Freshwater
Climate: Tropical
Biome: Small river ecosystems
Central latitude: 6.200000
Central longitude: -0.216700
Duration: 2 years, from 1970 to 1971

179 records

27 distinct species

Across the time series Chironomidae is the most frequently occurring species

Methods

The benthic fauna of the river was sampled using a Surber Stream-bottom sampler (Surber, 1937). The area enclosed by the rectangle of the net frame was 40 cm long by 25 cm wide making 1000 cm2. The net was of nylon bolting cloth with aperture size approximately 0-25 to 0-28 mm, approximately 35 mesh cm-1; equivalent to the number 60 mesh Tyler screen and U.S. Sieve 60. The sites for sampling were selected at random across the width of the stream and along the length of the sampling station but were at the same time chosen for their suitability to the sampler. The substrate was generally a flat horizontal sandstone with some cracks and steps which were more or less covered in the fast flowing sections with moss and various algae. The substrate was scraped from the rock into the net downstream using a spatula. The contents of the net were emptied into a collecting pan containing water from the river and the animals picked from the pan with forceps and rubber bulb pipettes, care being taken to check all surfaces of leaves, moss and pebbles. If the sample contained significant quantities of sand and/or silt the net was first emptied in portions into a number 60 sieve, each portion being thoroughly washed by passing water repeatedly through the sieve and swilling around the contents. The sand and detritus retained were then carefully picked over in the collecting pan. All samples were preserved in the field in 5 % formaldehyde. There was great variation between different Surber samples collected on the same date from the same station as a result of the many diverse microhabitats which occurred within a small area of the river bed. On each of the majority of sampling occasions at least three Surber samples were therefore taken from approximately similar areas of the river bed and in conditions of similar current velocity. In addition to the Surber samples non-quantitative samples were taken with a triangular, aluminium hand net mounted on a long handle and made of nylon netting with aperture size of 0-30 mm. Collections were made by sweeping twice over a distance of 1-2 m whilst scraping and stirring up the bottom upstream with a booted foot. These samples were used to supplement the observations of the quantitative Surber samples. Samples were sorted and counted in the laboratory. For purposes of identification, especially amongst the Chironomidae, some of the animals or parts of them were selected and mounted in Euparal on glass slides after boiling in 10% potassium hydroxide; they were then examined with a microscope. Changes in composition and numbers of the benthic fauna were investigated over a period of 17 months. Most of the following discussion is based on the results of the approximately monthly Surber samples and supplemented by the results of occasional non-quantitative hand samples (Table I). Some aspects of the cycles of change of the fauna were inferred from drift samples, light and emergence catches which were collected in conjunction with the benthic samples. The results from January to April 1970 are based on only one Surber sample (with the exception of 3 March 1970) and therefore are less reliable than those of all subsequent months. Three sets of samples in May 1971 are based on four Surber samples. However, total numbers of animals and the data presented in Table 1 and Fig. 2 have been converted to be the numbers expected or actually coUected from three Surber samples, that is, number of animals per 3000 cm^. The velocity of the current of the river was measured on each sampling occasion at the surface by the simple method of floating a ping-pong ball and timing its passage over a measured distance of several metres with a stop-watch. This was repeated twice and the average of three trials gave a reasonable approximation to the value of the surface current which is in tum indicative of the conditions throughout the flowing water column.”[Extracted from Hynes, 1975] NOTE: the data collected in the sampling events for which 1 or 4 Surber samples were taken are not included due to sampling effort being different to the main period of monitoring. Qualitative samples are also not included. Therefore, this dataset corresponds to the sampling events between May 1970 and May 1971 when three sets of Surber samples were examined.

Citation(s)

@Article{BioTIME_cit661, Study_id = {794}, Citation_id = {661}, Author = {Hynes, Julian}, Journal = {Freshwater Biology}, Pages = {71-83}, Title = {Annual cycles of macro-invertebrates of a river in southern Ghana}, Volume = {5}, Year = {1975}, Doi = {10.1111/j.1365-2427.1975.tb00122.x}, Language = {English} }