The adequacy of different methods of sampling invertebrates for the collection of qualitative and quantitative information for surveillance purposes has been the centre of discussion at Craig Goch Surveys Group meetings (Abel, 1975). This paper compares two methods of collecting macro-invertebrates from the R. Wye

Craig Goch Field Surveys Group

Slater, Frederick Maurice

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Craig Goch Field Surveys Group Meeting – Malvern 3-4 February 1976  UWIST Paper 3  Comparison of two methods of collecting macro-invertebrates from the R. Wye  Introduction  The adequacy of different methods of sampling invertebrates for the collection of qualitative and quantitative information for surveillance purposes has been the centre of discussion at Craig Goch Surveys Group meetings (Abel, 1975).  This paper compares two methods of collecting macro-invertebrates from the R. Wye.  Methods and Sites  Samples were collected from riffles using a cylinder sampler, modified after Neill (1938), and a kick sampling technique.  The cylinder sampler comprised of a metal cylinder with a serrated base which when driven and rotated into the substratum enclosed an area of 0.05m2.  The enclosed substratum was vigorously disturbed and dislodged macro-invertebrates were swept downstream into a detachable net (aperture size 400u) by water flowing through an upstream gauze window.  Attached organisms e.g. Hydropsyche spp. were removed from stones by hand.  Four cylinder samples were taken across the width of each riffle.  This technique has been used by UWIST in their surveillance programme of the R. Wye and tributaries in 1975.  Kick samples were taken by disturbing the substratum in front of a hand net (aperture size 400µ) for a fixed period of three minutes whilst moving upstream.  Thus, a ‘ribbon’ of riffle, generally some 15.0m in length and 0.3m in width, was sampled.  This sampling technique has been used by Severn-Trent Water Authority in their surveillance programme of the R. Severn and its tributaries.  The area sampled is about 5m2 (Abel, 1975).  After collection all samples were returned to the laboratory, preserved in 5% formaldehyde solution and sorted by hand.  The time taken to collect and sort each sample was recorded.  Sampling was carried out on 8th October 1975 at three sites on the R. Wye: Pant Mawr (7km from source), Rhayader (34km from source) and Glasbury (85km from source).  The discharge at Rhayader was 4.5 cumec, equivalent to 0.74 x A.D.F.  Results Table 1 indicates that 1.3 to 2.4 times more macro-invertebrates were collected in kick samples, covering an area of about 5m2, than in four cylinder samples, equivalent to an area of 0.2m2 and this was reflected in the longer time spent sorting kick samples.  Kick samples contained more extraneous material than cylinder samples, e.g. leaves, which made sorting more difficult.  The time taken to collect the different samples in the field was similar.  At all sites there were more species or species-groups collected in the cylinder samples (Table 1), and, although at different sites both sampling methods collected taxa which were exclusive to each technique the cylinder samples always contained a greater number of exclusive taxa.  Except for species or species-groups of Oligochaeta, which were consistently exclusive to cylinder samples, there were no other groups of macro-invertebrates which could be exclusively associated with the sampling method.  Table 2 indicates that the proportions of Ephemoptera and Plecoptera in kick samples were always greater than in cylinder samples and the proportion of Oligochaeta in cylinder samples was always greater than in kick samples.  No other generalisation can be made from these data.  Assuming that kick sampling collects animals from 5m2 of river bed some comparison of estimates of macro-invertebrate density can be made between the two sampling methods (Table 3).  Total density estimates from kick samples were 10 to 20 times lower than estimates of mean total density made from cylinder samples.  Discussion  It might seem logical that the larger the area of sampling (implicitly related to the number of microhabitats) and the more animals collected, the greater the number of taxa recorded.  For any one sampling procedure this would be true (Edwards, Hughes & Read, 1975) but it does not follow that in a comparison of two sampling procedures the more extensive will yield more taxa.  In the current study the cylinder sampler is not only more efficient in terms of taxa recovered per unit area or per individual; it recovers more in 0.2m2 than the kick-sampling method in about 5m2.  This results from the low recovery efficiency, only 5-10% (Table 3), of kick sampling, which creates an opportunity for selectivity of recovery of animal types: this more than compensates for the larger area covered by the kick sampling procedure.  Another conclusion from the data presented here is that a more rigorous taxon list is likely to result from increasing the number of cylinder samples than extending the time spent, or area covered, in kick sampling for cylinder samples are 10-20 times more efficient in recovering animals from a specific area and their ratio of taxa : individuals is higher.  The criticism in their use has been the very limited area and range of microhabitats sampled.  Table 1 shows that in terms of sorting time, the number of cylinder samples could be approximately doubled before post-treatment time exceeds that of the current kick-sampling procedure.  This doubling would also improve the confidence limits of population estimates.  This very limited study of the two sample methods cannot be accepted as universally applicable and it should be extended to other sites and seasons.  Nevertheless the demonstrably low efficiency of recovery of animals in kick-sampling procedures provides an opportunity for environmental and biological variables to operate on this efficiency.  This difference in efficiency is suggested in Table 3 for sites sampled in the current investigation.  Therefore acceptance that this kick-sampling method can be used in a comparative quantitative manner, providing the procedure is standardized, is very doubtful.  The qualitative pattern of recovery shown in Table 2 supports Armitae et al (1974) who concluded that the poor representation of Oligochaetes in kick samples probably results from fragmentation.  In addition, in this study, where Oligochaete species or species-groups were exclusive to a sampling technique at a station, this was always the cylinder.  Conclusion In the R. Wye, at sites and at the time investigated, the standardized kick-sampling procedure, as used by the Severn-Trent team, is less efficient than the cylinder sampling routine adopted by the UWIST group in terms of the number of taxa recovered.  Furthermore, cylinder samples take less time to sort.  The claim that ‘if kick-sampling is standardized it can be regarded as comparatively quantitative’ is highly dubious.  References Able, R. (1975).  The invertebrate programmes of the Severn and Wye.  Craig Goch Field Surveys Group.  22.9.75.  Armitage, P.D., Machale A.M. & Crisp D.C. (1974).  A survey of stream invertebrates in the Cow Green basin (upper Teesdale) before foundation.  Freshwat, Biol. 4, 369-398.  Edwards, R.W., Hughes, S.D. & Read, M.W. (1975).  Biological survey in the detection and assessment of pollution.  139-156, in: The Ecology of Resource Degradation and Renewables.  Eds: Chadwick, M.J. & Goodman, G.T.  Blackwell Scientific Publ.  1975.  Neill, R.M. (1938).  The food and feeding of brown trout (Salmo trutta L.) in relation to the organic environment.  Trans. R. Soc., Edinburgh, 59, 481-520.  Table 1  Comparison of Cylinder and Kick Samples  Total No. of individuals collected Total No. of species or species-groups collected Exclusive species or species-groups collected Sorting time (h) Site C K     C K C K C KPant Mawr  65        100 21 18 7 4 0.5 1.25Rhayader  296        693 35 30 11 6 1.75 3.5Glasbury  850        1069 55 54 7 6 2.0 4.0 C = 4 cylinder samples  K = 3 minute kick sample  Table 2  % representation of total number of macro-invertebrates collected   Pant Mawr Rhayader Glasbury  C K C K C K Platyhelminthes 6.2 15.5 1.0 3.1 - - Oligochaeta 18.8 7.0 24.6 1.2 15.4 13.0 Hirudinea 0 0 0 0 1.6 1.2 Plecoptera 6.2 17.2 8.7 18.3 0.5 1.3 Ephemeroptera 0 0 30.1 47.9 10.1 12.9 Trichoptera 11.6 16.1 12.1 7.8 34.1 35.2 Coleoptera 10.4 3.0 12.5 13.4 6.8 4.2 Crustacea 0 0 0 0 3.1 5.3 Chronomidae 14.5 13.3 3.7 1.1 15.4 10.4 Simulidae 29.0 17.1 3.3 0.7 4.2 6.0 Mollusca - - - - 7.8 8.8 Others 3.3 10.8 3.1 5.9 1.0 1.7  -  = included in others C = 4 cylinder samples K = 3 minute kick sample   Table 3  Total density estimates from cylinder (C) and kick (K) samples  Cylinders (No./m2) Site  1  2  3  4 _ x  S.E. Kick (No./m2) C K Pant Mawr  280 220 240 260 250 13 20 12.5 Rhayader  1040 1640 1780 1460 1480 161 139 16.5 Glasbury  3700 3000 4540 5760 4250 594 214 19.9  _ x   = arithmetic mean  S.E. = standard error of mean  

Craig Coch Field Surveys Group meeting, Malvern 3-4 February 1976: UWIST Paper 3. Comparison of two methods of collecting macro-invertebrates from the R. Wye

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Craig Coch Field Surveys Group meeting, Malvern 3-4 February 1976: UWIST Paper 3. Comparison of two methods of collecting macro-invertebrates from the R. Wye

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