THE APPLICATION OF SYSTEMATIC SAMPLING TO A STUDY OF 

 INFAUNA VARIATION IN A SOFT SUBSTRATE ENVIRONMENT^ 



Stephen Scherba, Jr.^ and Vincent F. Gallucci^ 

 ABSTRACT 



Stratified systematic sampling was applied to an intertidal macrofauna sediment study. A stratified 

 systematic sampling plan retains the advantages of the more common fixed level transect sample, and 

 possesses additional advantages which recommend it for use in some, intertidal studies. The field data 

 collected in this study demonstrated the effectiveness of stratified systematic sampling for quantifying 

 both sediment and population characteristics along a sediment gradient, and for the testing of 

 biological hypotheses. 



Intraarea, interarea, and interseason hypotheses about sediment composition were tested in terms of 

 particle size distributions. Populations of bivalves and polychaetes were simultaneously sampled and 

 hypotheses concerning spatial and seasonal variations in an intertidal mud flat were tested. 

 Experimental results using stratified systematic sampling suggest that Newell's hypothesis can be 

 extended to encompass temporal variation. Fine sediment grades (silty areas) may act to insulate 

 infauna against the extremes of seasonal stresses. 



Sediment composition, as measured by the average percentage composition by weight of various 

 grain sizes, was not sufficient to predict macrofaunal presence. 



The study of the complex relationship existing 

 between macrofauna (e.g., bivalves and poly- 

 chaetes) and their soft substrate environment is of 

 wide interest in marine biology. Soft sediments 

 are both a shelter from predators and a food source 

 for deposit feeders. The particle size distribution 

 of the sediment influences such factors as food 

 availability, the depth of the aerobic layer, water 

 content, pH differentials, and growth rates. De- 

 trital content and particle size distribution of the 

 sediment are largely determined by the hy- 

 drodynamics of currents. However, Rhoads (1967) 

 demonstrated that macrofauna modify sediment 

 stability, composition, and water content by ac- 

 tivities such as building tubes, ingesting sediment 

 and detritus (to remove bacteria from sediment 

 particles), depositing feces, etc. The particle size 

 distribution of the sediment is, therefore, one 

 measure of certain types of biological activity 

 (Newell 1965). 



Studies in soft substrate environments usually 

 involve sediment samples which contain large 

 numbers of macrofaunal species in different den- 

 sities as well as different particle size distribu- 



'Contribution No. 430 of the College of Fisheries, University of 

 Washington, Seattle, WA 98195. 



-The Department of Physiology and Biophysics, University of 

 Washington, Seattle, WA 98195. 



^College of Fisheries and The Center for Quantitative Science, 

 University of Washington, Seattle, WA 98195. Send reprint 

 requests to this address. 



Manuscript accepted April 1976. 



FISHERY BULLETIN: VOL. 74, NO. 4, 1976. 



tions. Then, it may be necessary to make compar- 

 isons between samples which may call for the use 

 of statistical methods as found in standard text- 

 books (e.g., Sokal and Rolf 1969). The validity of 

 tests of comparisons, however, must rest upon the 

 application of valid sampling plans in the field, but 

 most valid sampling plans do not meet the needs 

 of the ecologist. This paper reports on the use of 

 stratified systematic sampling which, to our 

 knowledge, is heretofore unused in the marine 

 literature. Stratified systematic sampling seems 

 to meet the needs of most studies that would have 

 used transecting methods which, generally, are 

 statistically unacceptable. The sampling method is 

 applied to a study of animal and sediment 

 gradients' in a basically marine embayment sub- 

 ject to seasonal variation in density of animals and 

 algae. Hypotheses comparing areas of different 

 sediment composition in the winter, spring, and 

 summer are tested using animal-presence and 

 sediment-particle-size data collected using a 

 stratified systematic sampling plan. The bay is 

 shown to contain a sediment gradient from fine 

 silt to coarse sand, with an associated polychaete 

 distribution expressed by both the number of 

 animals per species and by the number of species 

 found. 



A variety of sampling methods are described in 

 the literature. For example, the works of Skellam 

 (1958) and Sen et al. (1974) presented different 



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