Despite the global occurrence of braided rivers and the frequency with which they are anthropogenically modified, the benthic diversity of their floodplains and, in particular, lateral and longitudinal patterns in their communities have been neglected. A spatially nested, hierarchical survey was conducted of 11 braided rivers in the South and North Islands of New Zealand to investigate benthic invertebrate diversity at multiple spatial scales. In each river, 6 reaches and up to 5 floodplain habitat types within each reach were sampled. From a total of 203 sites, 145 taxa were identified. Benthic invertebrate diversity was highly variable at the island, river, reach, and habitat scales. Diversity differences between islands were driven by high regional endemism. Diversity at the whole-river scale ranged from 99 taxa in the Wairau River to only 56 in the Waiapu River. At the reach scale, no significant differences in diversity or abundance were found longitudinally down the rivers. At the habitat scale, lateral floodplain habitats, particularly spring creeks, consistently had greater richness and abundance than did adjacent main channel habitats. Comparisons of Whittaker's multiplicative β at different spatial scales revealed that the greatest range and mean value of taxon turnover was among habitats within reaches. Additive partitioning of β diversity indicated that diversity values at the broad spatial scales of reach and river contributed disproportionately to overall diversity. Our results indicate that river managers concerned with maintaining diversity should focus their efforts at the whole-river scale rather than attempting management of smaller units representing local scales. However, at finer scales, lateral floodplain habitats (particularly springs and floodplain ponds) are hot spots of diversity and protection and remediation of these habitats are particularly important.
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