Taxonomic level and sample size sufficient for assessing pollution impacts on the Southern California Bight macro-benthos

Publisher Website
Google Scholar
Abstract
Macrobenthic data from samples taken in 1980, 1983 and 1985 along a pollution gradient in the Southern California Bight (USA) were analyzed at 5 taxonomic levels (species, genus, family, order, phylum) to determine the taxon and sample size sufficient for assessing pollution impacts on 5 measures of community structure. Two statistical designs were compared: a t-test for differences between reference and impacted stations where the error terms was (1) among-year variation at the reference station (impact effects design), (2) replicate (within-station) sampling error (location effects design). The estimated statistical power (1-.cxa..beta.) to detect impacts was a function of type and magnitude of impact, level of taxonomic identification, the statistical design, and the sample size (ni = number of sampling years at the reference station for the impact effects design, and n1 = number of replicate samples per station for the location effects design). Four replicate 0.1 m2 van Veen grabs per station were needed to ensure community-wide, unbiased estimates of Shannon''s, 1-Simpson''s and McIntosh''s Index. Family-level identification appeared to be a good choice for assessing pollution impacts at the study sites as it ensured a high probability (1 - .beta. .gtoreq. 0.80) of detecting intermediate or larger impacts on most (impact effects design) or all (location effects design) of 5 measures of community structure when nl and ni .gtoreq. 4. The level of taxonomic identification and sample size should be considered along with other sampling variables (e.g. sample unit size, sieve mesh size) when seeking a statistically rigorous, cost-effective study design sufficient to meet pollution assessment objectives.
Keywords