A comparison of some methods commonly used for the collection of sublittoral sediments and their associated fauna
Somerfield, P.J.; Clarke, K.R. (1997). A comparison of some methods commonly used for the collection of sublittoral sediments and their associated fauna. Mar. Environ. Res. 43(3): 145-156
Five replicate samples were collected using each of four different collection methods, at two sites with contrasting sediment types, namely soft mud and hard muddy sand. The four methods were: 1. direct collection by divers; 2. collection using a Craib corer; 3. subsampling from an USNEL pattern box corer; and 4. subsampling from a van Veen grab. As far as possible, biasing factors, other than the actual sampling operation at the sediment surface, were controlled. Nematodes in the samples were identified and the resulting data analysed using a range of techniques. Univariate measures of community structure, such as diversity indices, did not reveal any significant difference between sampling methods, neither was any significant difference detected in diversity profiles (k-dominance curves). The conclusion which might be drawn from these experiments is that it makes little difference which method of sampling is chosen for a particular study. Such a conclusion would be erroneous, as multivariate analyses did reveal significant differences in community structure between samples retrieved by different methods. The patterns of differences at the two sites were dependent, in detail, on the transformations used in the analyses, but in general there was a smooth shift in community structure from cores collected by divers, through Craib cores and box-core subsamples, to subsamples from grabs. The detected differences, although significant, were small, and did not suggest a strong, or ecologically meaningful, explanation. A modified index of multivariate dispersion is described, and this is used to examine differences between sampling methods in intra-sample variability. This showed that differences in variability contribute to, but do not fully explain, the observed differences. It should also be borne in mind that factors which might not be expected to affect different samplers in the same way, such as water depth, weather conditions and sample size, were controlled. It is likely that these have biasing effects as important as the actual operation of sampling gear on the seabed, where explanations of the differences between sample quality from different methods, such as bow-wave effects, have been focused.
