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Marine Ecology Progress Series

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MEPS 523:15-30 (2015)  -  DOI:

Biotic interactions influence sediment erodibility on wave-exposed sandflats

Rachel J. Harris1,*, Conrad A. Pilditch1, Judi E. Hewitt2, Andrew M. Lohrer2, Carl Van Colen4, Michael Townsend2, Simon F. Thrush3

1School of Science, University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand
2National Institute of Water and Atmospheric Research Ltd. (NIWA), PO Box 11115, Hamilton 3240, New Zealand
3Institute of Marine Science, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
4Research Group of Marine Biology, Ghent University, Krijgslaan 281/S8, 9000 Ghent, Belgium
*Corresponding author:

ABSTRACT: Biological activities in marine soft-sediments can modify the sedimentary environment through processes that change erosion rates. In low-energy environments, bioturbating macrofauna destabilizes sediments while microbes bind sediments and stabilize them. The degree to which these counter-acting processes influence sediment movement in a physically dynamic environment has not been well quantified. In a field experiment, we established 56 (1 m2) plots on an exposed intertidal sandflat. We used shade cloth and manipulated grazing pressure exerted by the deposit-feeding bivalve Macomona liliana (0-200 ind. m-2) to alter the microphytobenthic community. Three months post-manipulation, initiation of sediment transport (Ʈc) and change in sediment erosion rate with increasing bed shear stress (me) were measured. Mean grain size, density of the spionid polychaete Aonides trifida, density of adult M. liliana, and bulk carbohydrate concentration could account for 54% of the variation in Ʈc (0.3-1.1 N m-2 s-1). Mean grain size was the only significant predictor (p ≤ 0.01) of me explaining 22% of the variability (6-20 g N-1 s-1). Ʈc was negatively correlated with density of several abundant shallow-dwelling bioturbators (indicating sediment destabilization), but we did not observe the expected increase in Ʈc with microbial biomass. Furthermore, there was a positive correlation between adult M. liliana and Ʈc as well as evidence for several positive feedbacks between abundant shallow-dwelling macrofauna and microbial biomass. These study results demonstrate that despite frequent reworking by tidal currents and waves, bioturbating macrofauna are important to initiating sediment transport regardless of their effects on microbial biomass.

KEY WORDS: Deposit-feeding · Microphytobenthos · Benthic macrofauna · Sediment stability · Infauna · Positive feedbacks · Macomona liliana · Habitat modifiers

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Cite this article as: Harris RJ, Pilditch CA, Hewitt JE, Lohrer AM, Van Colen C, Townsend M, Thrush SF (2015) Biotic interactions influence sediment erodibility on wave-exposed sandflats. Mar Ecol Prog Ser 523:15-30.

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