Rapid Biological Assessments: How Many Animals Are Enough?

Somers, Keith M.; Reid, Ron; David, S. M.

doi:10.2307/1468337

Cited by 48 publications

(39 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…This result has serious implications for wetland bioassessment because 100-organism fixed counts have become widely used among state (e.g., FDEP 1996), regional (e.g., Maxted et al 2000), and federal (e.g., Plafkin et al 1989) protocols for streams in the USA. Other studies have concluded that the 100 count can be equally informative as larger counts for lakes and streams (Barbour and Gerritsen 1996, Growns et al 1997, Somers et al 1998, Sovell and Vondracek 1999, but these studies only considered the ability of subsamples to discriminate differences in mean values of specific metrics among Ն2 levels of impairment. None of these studies statistically compared the magnitude of a test statistic or evaluated accuracy among subsamples.…”

Section: Evaluating Subsampling Approachesmentioning

confidence: 99%

“…Nevertheless, subsampling is still a source of much contention among managers and biologists (Barbour and Gerritsen 1996, Courtemanch 1996, Vinson and Hawkins 1996, Growns et al 1997, Walsh 1997, Somers et al 1998, Sovell and Vondracek 1999, Doberstein et al 2000. Much of this debate has arisen from the use of fixedcount subsampling, a method in which random cells in a sorting pan are picked until a target number of organisms (e.g., 100) is obtained.…”

mentioning

confidence: 99%

“…Others have demonstrated that metric values calculated from fixed counts are highly variable and perhaps misleading when Ͻ300 individuals are obtained (Doberstein et al 2000). However, still others have maintained that the cost-saving benefits of fixed-count processing outweigh the potential loss of information (Barbour and Gerritsen 1996), with some studies showing that even 100-organism bioassessments were able to distinguish sites of differing ecological impairment (Growns et al 1997, Somers et al 1998) and produce stable values for metrics when compared to larger counts (Sovell and Vondracek 1999).…”

mentioning

confidence: 99%

See 2 more Smart Citations

Evaluating Subsampling Approaches and Macroinvertebrate Taxonomic Resolution for Wetland Bioassessment

King¹,

Richardson²

2002

Journal of the North American Benthological Society

153

114

View full text Add to dashboard Cite

Abstract. Methods for wetland bioassessment using macroinvertebrates are not well developed. Two of the most controversial issues in stream bioassessment, subsampling and taxonomic resolution, have yet to be quantitatively addressed for wetlands. Using a multivariate approach, we evaluated the efficacy of family-, genus-, and species-level assemblage data in reflecting the environment and distinguishing impaired sites from the reference condition. We used 5 basic levels of subsampling (100-, 200-, and 300-organism fixed counts; 10% and 25% fixed areas), an integrated subsample requiring a minimum fixed count and fixed area (100&10%), and 100-count and 10%-area subsamples coupled with a supplementary large-rare (LR) search. Data were obtained from 1.5-m 2 composite samples collected from 126 plots along a 10-km-long eutrophication gradient in the Florida Everglades. Our results suggest that effectiveness of subsampling depended more upon the minimum number of individuals retained than minimum area or proportion of the sample picked. Fixed-area subsamples were generally less efficient than fixed counts, with 200-and 300-individual fixed counts resulting in significantly greater assemblage-environment relationships and much higher accuracy in detecting impairment than 10% fixed area, despite averaging similar numbers of individuals. The greatest improvement with increasing subsample size was observed between fixed counts of 100 and 200 individuals; detecting impairment, in particular, was not markedly improved with subsample sizes Ͼ200 individuals. Supplementing subsamples with a LR search resulted in only very slight improvements in assemblage-environment relationships, but was effective in improving prediction accuracy, particularly for family-level data. However, family-level assemblage-environment relationships and abilities to detect impairment were inferior to genus-and species-level data, regardless of subsample size. Species-level data performed best, primarily because of the large proportion (Ͼ20%) of total species belonging to Chironomidae. The potential importance of Chironomidae to wetland bioassessment was further revealed through an evaluation of a tiered-taxonomic approach, which showed that non-Chironomidae family-level data tiered with species-level Chironomidae data produced results very similar to those obtained using genus-or species-level data exclusively. Our results suggest that fixed counts Ն200 or integrated fixed-area/fixed-count approaches that consistently obtain a minimum of 200 individuals should be considered as minimum subsample sizes for wetlands. We additionally advocate LR searches and recommend genus-or species-level taxonomy, particularly for the Chironomidae.

show abstract

Section: Evaluating Subsampling Approachesmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Evaluating Subsampling Approaches and Macroinvertebrate Taxonomic Resolution for Wetland Bioassessment

King¹,

Richardson²

2002

Journal of the North American Benthological Society

153

114

View full text Add to dashboard Cite

show abstract

“…However, their routine use in the biomonitoring of lake systems is much less extensive and practically restricted to North America, where various authors have used or proposed the use of multimetric indices based on benthic invertebrates (Pinel-Alloul et al, 1996;David et al, 1998;Somers et al, 1998;Burton et al, 1999;King et al, 2000). Similarly, a number of studies have reported significant correlations between lake macroinvertebrate fauna and levels of different types of pollution (Kornij !…”

Section: Introductionmentioning

confidence: 99%

Plant-associated invertebrates and ecological quality in some Mediterranean shallow lakes: implications for the application of the EC Water Framework Directive

García-Criado

Bécares

Fernández‐Aláez

et al. 2004

Aquatic Conserv: Mar. Freshw. Ecosyst.

View full text Add to dashboard Cite

“…In most cases a decrease in the costs of biological monitoring programs has been achieved by limiting the number of samples or restricting the number of organisms picked (Metzling & Miller, 2001). The implications of these measures to reduce costs have been the subject of many studies (e.g., Needham & Usinger, 1956;Chutter, 1972;Elliot, 1977;Somers et al, 1998;Lorenz et al, 2004). The implications of reducing the physical sample size, however, have hardly been studied.…”

Section: Introductionmentioning

confidence: 99%

Influence of macroinvertebrate sample size on bioassessment of streams

Vlek¹,

Šporka

Krno

2006

The Ecological Status of European Rivers: Evaluation and Intercalibration of Assessment Methods

View full text Add to dashboard Cite

In order to standardise biological assessment of surface waters in Europe, a standardised method for sampling, sorting and identification of benthic macroinvertebrates in running waters was developed during the AQEM project. The AQEM method has proved to be relatively time-consuming. Hence, this study explored the consequences of a reduction in sample size on costs and bioassessment results. Macroinvertebrate samples were collected from six different streams: four streams located in the Netherlands and two in Slovakia. In each stream 20 sampling units were collected with a pond net (25Â25 cm), over a length of approximately 25 cm per sampling unit, from one or two habitats dominantly present. With the collected data, the effect of increasing sample size on variability and accuracy was examined for six metrics and a multimetric index developed for the assessment of Dutch slow running streams. By collecting samples from separate habitats it was possible to examine whether the coefficient of variation (CV; measure of variability) and the mean relative deviation from the ''reference'' sample (MRD; measure of accuracy) for different metrics depended only on sample size, or also on the type of habitat sampled. Time spent on sample processing (sorting and identification) was recorded for samples from the Dutch streams to assess the implications of changes in sample size on the costs of sample processing. Accuracy of metric results increased and variability decreased with increasing sample size. Accuracy and variability varied depending on the habitat and the metric, hence sample size should be based on the specific habitats present in a stream and the metric(s) used for bioassessment. The AQEM sampling method prescribes a multihabitat sample of 5 m. Our results suggest that a sample size of less than 5 m is adequate to attain a CV and MRD of £ 10% for the metrics ASPT (Average Score per Taxon), Saprobic Index and type Aka+Lit+Psa (%) (the percentage of individuals with a preference for the akal, littoral and psammal). The metrics number of taxa, number of individuals and EPT-taxa (%) required a multihabitat sample size of more than 5 m to attain a CV and MRD of £ 10%. For the metrics number of individuals and number of taxa a multihabitat sample size of 5 m is not even adequate to attain a CV and MRD of £ 20%. Accuracy of the multimetric index for Dutch slow running streams can be increased from £ 20 to £ 10% with an increase in labour time of 2 h. Considering this low increase in costs and the possible implications of incorrect assessment results it is recommended to strive for this £ 10% accuracy. To achieve an accuracy of £ 10% a multihabitat sample of the four habitats studied in the Netherlands would require a sample size of 2.5 m and a labour time of 26 h (excluding identification of Oligochaeta and Diptera) or 38 h (including identification of Oligochaeta and Diptera).

show abstract

Rapid Biological Assessments: How Many Animals Are Enough?

Cited by 48 publications

References 19 publications

Evaluating Subsampling Approaches and Macroinvertebrate Taxonomic Resolution for Wetland Bioassessment

Evaluating Subsampling Approaches and Macroinvertebrate Taxonomic Resolution for Wetland Bioassessment

Plant-associated invertebrates and ecological quality in some Mediterranean shallow lakes: implications for the application of the EC Water Framework Directive

Influence of macroinvertebrate sample size on bioassessment of streams

Contact Info

Product

Resources

About