Qualitative and quantitative studies of benthic infaunal communities in British Columbia coastal waters




Burd, Brenda Jean

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In this study, I examine and compare benthic infaunal and environmental factors from the British Columbia coastline on a broader geographic and temporal scale than has been attempted in this area. The hypothesis that large and small macrofauna are distributed differently under different environmental conditions was examined by comparing results based on numerical abundance and biomass-weighted abundance data. Both data methods have drawbacks, but their combined use nullified the primary bias of each. I concluded that the combined results from numerical and biomass-weighted data provided a clearer picture of faunal and environmental interactions than either result alone. The faunal data were analysed using cluster analysis in conjunction with an inferential bootstrap method called Sigtree, which places significance values on the cluster groupings. The multivariate results from both faunal data formats were compared to each other using a second non-parametric bootstrap method, Comtre2. Finally the two faunal dendrograms were inferentially compared with a dendrogram derived from environmental data, using the method Comtre1. The above analyses were conducted independently on the two faunal datasets from each survey area, then for data from all survey areas combined. I have included a discussion of the potential effects of sampling parameters on the results of inferential analyses, power and overall significance of the tests, and suggested an optimum approach for future studies. The Sigtree analyses of significant cluster groups was the most valuable of the three inferential methods used, and was least affected by the multiple comparisons problem. The major drawback of this and other bootstrap methods is their dependence on the raw data being manipulated. Despite the limitations of the method, the results of Sigtree analyses were believable and readily interpretable. The Sigtree analyses of the combined data for all survey areas indicated that most stations within a given survey area remained grouped together. Exceptions illustrated the consistency in faunal composition (including impoverishment) which may be expected for areas with similar environmental conditions, regardless of the geographic distance between stations. Results often revealed very different patterns in the distribution of small versus large fauna, particularly in disturbed areas such as Alice Arm and Vancouver Harbour, and in cases where only the small fauna or only the large fauna were impoverished. However, the Comtre2 comparison of results for the two data management approaches lacked sufficient discrimination to distinguish between the distribution patterns of large and small fauna for any survey area except Alice Arm. As well, the multiple comparisons problem was serious for Comtre2 for sets of data with many stations. The Comtre1 results suggested that the distribution patterns of large fauna were more closely predicted than the distribution of small fauna, by the environmental factors measured. I concluded that Comtre1 was of limited use for the environmental data available (sediment particle size, depth and location) for all survey areas, but was of considerable value for interpreting relationships between complex sediment chemistry factors and the distribution of large fauna. The Comtre1 results were considered unreliable for analyses with many stations, because of the multiple comparisons problem. Using the methods outlined in this study, comparisons of mactofaune structure from different habitat types and geographic locations were feasible and informative even though sampling conditions were variable. The data management approach used to examine patterns in different size components of the assemblage could be expanded to focus in greater detail on size-related structural complexities within benthic communities.



Benthos, British Columbia, Marine animals, Ecology, British Columbia