New Zealand Journal of Geology and Geophysics abstracts

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Bathymetric distributions of modern populations of some common Cenozoic Bryozoa from New Zealand, and paleodepth estimation

Paul D. Taylor

Department of Palaeontology
The Natural History Museum
Cromwell Road
London SW7 5BD, United Kingdom

Dennis P. Gordon

National Institute of Water & Atmospheric Research
P.O. Box 14 901 Kilbirnie
Wellington, New Zealand

Peter B. Batson

Department of Marine Science
University of Otago
310 Castle St
Dunedin, New Zealand

Abstract  Paleodepth inference from fossils often involves application of the principle of taxonomic uniformitarianism using known depth ranges of modern populations belonging to the same or closely related species. Bryozoans are abundant on the continental shelf around New Zealand at the present day but their potential as paleodepth indicators in the Cenozoic, where they dominate many fossil assemblages, has not been explored. Here, we survey the bathymetric distributions of four readily identifiable and common species (Cinctipora elegans, Attinopora zealandica, Diaperoecia purpurascens, and Celleporaria emancipata) plus one distinctive ecological group of bryozoans (tube-building symbionts of hermit crabs), all of which are well represented in the Neogene fossil record of New Zealand. Data on the benthic stations containing these bryozoans in the extensive oceanographic collections at the National Institute of Water & Atmospheric Research reveals wide bathymetric distributions which constrain their use in estimating paleodepth from fossil occurrences. Total depth ranges were found to be: Cinctipora elegans, 17-914 m; Attinopora zealandica, 35-1156 m; Diaperoecia purpurascens, 0-1156 m; Celleporaria emancipata, 68-690 m; hermit crab tube builders, 0-252 m. A localised analysis of occurrences and abundances of Cinctipora elegans and Diaperoecia purpurascens off Otago Peninsula was also conducted. This analysis confirmed that these species occur over a large depth range on the Otago shelf. In C. elegans, colony abundance peaked strongly between 75 and 100 m off Otago Peninsula, a relatively narrow depth range. Despite their wide bathymetric distributions, several of the species surveyed here may eventually prove useful as paleodepth indicators because of their morphological plasticity which, by analogy with other bryozoans, is probably a response to environmental variables, some correlated with depth. Data are also presented on the geographic distributions of the target bryozoans.

Keywords  bryozoans; bathymetry; paleodepth analysis; New Zealand; Neogene; Cinctiporidae; Diaperoecia; Celleporaria; hermit crab symbionts

G02059; Online publication date 25 February 2004
Received 19 November 2002; accepted 28 October 2003
New Zealand Journal of Geology & Geophysics, 2004, Vol. 47: 57-69
0028-8306/04/4701-0057 © The Royal Society of New Zealand 2004

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