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Marine Ecology Progress Series

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MEPS 414:179-193 (2010)  -  DOI:

Habitat dependence in the functional traits of Austrohelice crassa, a key bioturbating species

H. R. Needham1,2,*, C. A. Pilditch1, A. M. Lohrer2, S. F. Thrush2

1Department of Biological Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand
2National Institute of Water and Atmospheric Research, PO Box 11-115, Hamilton, New Zealand

ABSTRACT: Bioturbating macrofauna can have major effects on their physical, biological and biogeochemical surroundings, altering ecosystem functioning. Burrow builders increase the amount of sediment–water interface over which oxidative exchange occurs, whilst organisms that ‘bulldoze’ through sediments homogenise and oxygenate the surface layers. Here we demonstrate that the bioturbating crab Austrohelice crassa performs the role of burrow builder in muddy and bulldozer in sandy sediments. Sediment reworking rates and expansion of the sediment–water interface through A. crassa bioturbation were estimated from 4 parameters: burrow and crab density, burrow morphology, burrow permanency, and burrow maintenance, measured across a sedimentary gradient. Burrow decay rates (k, d–1), in combination with differences in burrow and crab densities, were responsible for changes in sediment reworking rates among habitats. Mean burrow permanency (1/k) varied from 25.7 d in mud to 10.8 d in muddy sand to 1.4 d in sand. In mud, where adult burrow density was greatest (207 m–2) and structures were stable, A. crassa burrows extended the sediment–water interface by 147%, compared with 50% in muddy sand and 22% in short-lived sand burrows. In sand, 82% of the sediment available to A. crassa was mixed per lunar month (rising to 130% when including burrow maintenance values), whereas in mud and muddy sand, mean rates of sediment reworking dropped to 7.4%. These differences in the key bioturbational role of A. crassa between sediment types indicate that the impact of this species on ecosystem functioning will be highly habitat-dependent.

KEY WORDS: Austrohelice crassa · Bioturbation · Functional plasticity · Burrow permanency

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Cite this article as: Needham HR, Pilditch CA, Lohrer AM, Thrush SF (2010) Habitat dependence in the functional traits of Austrohelice crassa, a key bioturbating species. Mar Ecol Prog Ser 414:179-193.

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