Assemblages of animals around urban structures: testing hypotheses of patterns in sediments under boat-mooring pontoons

Assemblages of animals in soft-sediments were studied in relation to pontoo ns for mooring private boats in two estuaries near Sydney, Australia. Based on previously observed patterns around other types of artificial structure s, it was predicted that assemblages of animals under pontoons would be dif ferent from those in similar areas away from pontoons. Hypotheses about ove rall differences in average abundance and composition between sites with an d without pontoons were tested, as were hypotheses about variable differenc es among and within estuaries. Analyses revealed that there were fewer crus taceans under pontoons in one estuary. The most conspicuous patterns relate d to pontoons were, however, differences in variability among sites with po ntoons compared to sites without pontoons. Differences in spatial variabili ty were found for the overall multivariate structure using Bray-Curtis diss imilarities and for abundances of most major taxa. Total abundance was appr oximately 60 times more variable among sites without pontoons and number of taxa were seven times more variable among sites with pontoons. Such patter ns indicate that impacts of pontoons occur at some sites but not at others. This may be explained by intrinsic differences among sites or by differenc es in practices for maintenance. Predictions from these two contrasting mod els need to be tested in order to achieve efficient management of this type of structure. (C) 2001 Elsevier Science Ltd. All rights reserved.