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Marine Ecology Progress Series

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MEPS 358:125-136 (2008)  -  DOI:

Effects of seagrass beds (Zostera noltii and Z. marina) on near-bed hydrodynamics and sediment resuspension

John Widdows1,*, Nick D. Pope1, Mary D. Brinsley1, Harald Asmus2, Ragnhild M. Asmus2

1Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth PL1 3DH, UK
2Alfred Wegener Institute for Polar and Marine Research, Wadden Sea Station Sylt, Hafenstrasse 43, 25992 List, Germany

ABSTRACT: The main objectives of this flume study were to (1) quantify density dependent effects of the short-leaf seagrass Zostera nolti on hydrodynamics and sediment resuspension from a sandy bed, and (2) measure the erodability of 2 contrasting sediments (sandy and muddy) and the extent to which this is modified by the presence of 2 seagrass species, Z. noltii (sandy) and Z. marina (muddy). Field measurements of near-bed tidal currents, turbulence and suspended particulate matter at 2 different Z. noltii locations (low energy [sheltered] and higher energy [exposed] environments) were interpreted in the context of the flume results. Skimming flow above the high density bed of Z. noltii was accompanied by a 40% reduction in near-bed flow, but this was offset by a 2-fold increase in turbulent kinetic energy (TKE) and bed shear stress (τ0). Despite this increase in τ0 there was an increase in sediment stabilisation with increasing seagrass density (10-fold increase in critical bed shear stress for erosion [τe] from 0.1 [bare sediment] to 1.0 Pa at the highest shoot density). This was largely explained by the increased microphytobenthos abundance (reflected in the higher chlorophyll a and carbohydrate contents) and a lower density of the grazer and bio-destabiliser Hydrobia ulvae. In contrast, the muddy site was more easily eroded (10-fold higher), with Z. marina having little effect on sediment erodability (bare: τe = 0.05 Pa; Z. marina: τe = 0.07 Pa). This higher erodability was due to differences in hydrodynamics and the physical/biological properties of the sediment.

KEY WORDS: Seagrass beds · Zostera noltii · Zostera marina · Hydrodynamics · Sediment resuspension

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Cite this article as: Widdows J, Pope ND, Brinsley MD, Asmus H, Asmus RM (2008) Effects of seagrass beds (Zostera noltii and Z. marina) on near-bed hydrodynamics and sediment resuspension. Mar Ecol Prog Ser 358:125-136.

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