Spatial variation in burrow morphology of the mud shore crab Helograpsus haswellianus (Brachyura, Grapsidae) in South Australian saltmarshes
G. Katrak A C , S. Dittmann A and L. Seuront A BA School of Biological Sciences, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia.
B South Australian Research and Development Institute, Aquatic Sciences, West Beach, SA 5022, Australia.
C Corresponding author. Email: gitanjali.katrak@flinders.edu.au
Marine and Freshwater Research 59(10) 902-911 https://doi.org/10.1071/MF08044
Submitted: 22 February 2008 Accepted: 2 August 2008 Published: 27 October 2008
Abstract
Burrowing by crabs is an important component of their functional role in mangrove and saltmarsh habitats. The grapsid crab Helograpsus haswellianus (Whitelegge, 1889) is one of the more conspicuous burrowing organisms in the saltmarshes of southern Australia. To evaluate intraspecific differences in burrowing behaviour among saltmarshes on a regional scale, we compared vegetation cover, sediment composition and burrow morphology at four sites using resin casts. Six burrow morphology characters were measured (burrow depth, number, lengths and diameter of the shafts, ratio of the shafts, number and diameter of the burrow openings), and the overall 3D burrow complexity was described using a single parameter, the fractal dimension D. Apart from the number of shafts, all morphological characters of the burrows differed significantly among sites. Analyses of the fractal dimensions lead to the identification of three groups of burrows based on D: a group of highly complex burrows (one site), a group of burrows of intermediate complexity (two sites) and a group of less complex burrows (one site). Burrow morphology variation was correlated with non-dominant vegetation, plant matter in the soil and very coarse sand in the sediment. Site-specific differences in burrows caution against generalising the functional role of crabs across sites.
Additional keywords: burrows, crab, ecosystem engineer, fractals, resin cast, saltmarsh.
Acknowledgements
We would like to thank the Department of Environment and Heritage, Government of South Australia for access to the study sites (Permit number Z25067). Animal ethics permits were not required for this study. We thank Dr Volker Framenau of the Western Australian Museum and Dr David Hirst of the South Australian Museum for their help in identifying the spider species and Professor Peter Fairweather for assistance with some of the statistical analyses. We would also like to thank the referees for their helpful comments in improving this manuscript. This study was funded by grants from the Nature Foundation of South Australia and the ANZ Holsworth Wildlife Research Endowments.
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