Abstract On Karore Bank, an intertidal mud flat near Auckland International Airport, New Zealand, 40 faunal quadrats 0.5×0.5 m were dug, 21 of these being submitted to a grain-size analysis of the sediment. Twelve species of invertebrates (40 samples) were arrayed in 4 communities using principal component analysis. A reduced list of 8 species (21 samples) was grouped in the same manner and the communities correlated with sediment grade by multiple regression analysis. The two most clearly defined communities were characterized by Chione stutchburyi and Macomona liliana, and by Halicarcinus cookii and Owenia fusiformis. These were negatively correlated and associated respectively with coarse and fine sediments. The definition of the communities and their correlation with sediments was consistent with those which would have been obtained by conventional subjective methods, but the former extended the range of the conclusions. An analysis of the same data by canonical correlation appeared to produce less meaningful results, though this technique may well repay further investigation.