A preliminary investigation of diversity, abundance, and distributional patterns of chitons in intertidal boulder fields of differing rock type in South Australia

Abstract

The rock type of hard substrata marine habitats can affect numerous benthic invertebrates, but little is known of the effects on molluscan assemblages, for example, the chitons often found under intertidal boulders. We compared chiton assemblage composition, abundance, species richness, and patterns of frequency distribution in 10 boulder fields containing either hard metamorphic/igneous boulders or soft limestone boulders in two geographical areas in South Australia. Similar species richness occurred in both types of boulder fields, but hard rock boulder fields had greater overall abundances, because of particularly large abundances of some common species. Differences in abundances of common species also resulted in significantly different assemblages occurring between the boulder field types. Some species appeared aggregated among boulders, but this pattern was variable between boulders in differing areas and of differing rock type. In one area, a common species had variable aggregation that caused frequency distributions to differ significantly between boulders of different rock types. These results indicate that rock type needs to be considered when investigating ecological patterns and processes involving specialist molluscs such as under-boulder chitons and to ensure comprehensive marine reserve planning for protecting rare invertebrates in rocky intertidal reefs.

Keywords:

• habitat structure
• substratum
• under-boulder habitat
• Polyplacophora
• Ischnochiton
• conservation

Acknowledgements

This work was supported by Flinders University and was funded by a Nature Foundation SA grant to K.L. We appreciate the logistic support and advice from Martine Kinloch and Danny Brock from the Kangaroo Island Natural Resource Management Board. Peter Fairweather and Ross Coleman contributed useful discussion and statistical advice. We thank Angela Dutton for field assistance and Karen Gowlett-Holmes for advice with the identification of some chiton species. We also thank three anonymous reviewers for their advice which improved the earlier versions of the manuscript.

Additional information

Notes on contributors

Kiran Liversage

Current address: Centre for Research on Ecological Impact of Coastal Cities, Marine Ecology Laboratories (A11), University of Sydney, Sydney, New South Wales 2006, Australia