Modern bryozoan assemblages and distribution on the Lacepede Shelf, southern Australian margin

Abstract

Modem and relict sediments on the cool-water Lacepede Shelf are dominated by fragments of bryozoans, molluscs and foraminifers. This study evaluates the distribution of modem bryozoan sediment on the Lacepede Shelf based on 88 species from 16 localities using cluster analysis and principal component analysis. Six bryozoan faunal assemblages, corresponding roughly to physiographic position on the shelf, are recognized objectively. Assemblages are robust and generally defined by the changing diversity and relative abundance of the bryozoan fauna across the shelf. Slope assemblages can be differentiated from shelf assemblages based on presence or absence of a few key species. Lateral variation along the three transects is associated with: (i) differences in shelf geometry (shelf width, depth of shelf edge and angle of the slope); (ii) previous influx of continental sediments; and possibly (iii) presence of upwelling and long-shelf currents. Data were also evaluated to determine the level of detail required to provide the optimal information, with the most efficiency, from diverse bryozoan faunas. Presence- absence data for species prove nearly as effective in determining bryozoan assemblage distributions as analyses that incorporate taphonomic and abundance information. In addition, similar distribution patterns were observed using as few as 12 key species. The distribution of bryozoan species provides additional insight into the composition of carbonate skeletal particles on the Lacepede Shelf and the ecology of the diverse bryozoan fauna. These data are contributing to our understanding of the development of cool-water carbonates. © 1995 Taylor & Francis Group, LLC.