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Abstract
Assemblages of animals in soft-sediments were studied in relation to pontoons for
mooring private boats in two estuaries near Sydney, Australia. Based on previously
observed patterns around other types of artificial structures, it was predicted that
assemblages of animals under pontoons would be different from those in similar areas
away from pontoons. Hypotheses about overall differences in average abundance and
composition between sites with and without pontoons were tested, as were hypotheses
about variable differences among and within estuaries. Analyses revealed that there
were fewer crustaceans under pontoons in one estuary. The most conspicuous patterns
related to pontoons were, however, differences in variability among sites with pontoons
compared to sites without pontoons. Differences in spatial variability were found
for the overall multivariate structure using Bray-Curtis dissimilarities and for abundances
of most major taxa. Total abundance was approximately 60 times more variable among
sites without pontoons and number of taxa were seven times more variable among sites
with pontoons. Such patterns indicate that impacts of pontoons occur at some sites
but not at others. This may be explained by intrinsic differences among sites or by
differences in practices for maintenance. Predictions from these two contrasting models
need to be tested in order to achieve efficient management of this type of structure.