Influence of the small intertidal seagrass Zostera novazelandica on linear water flow and sediment texture

Abstract

The influence of a small intertidal seagrass, Zostera novaz.elandica (Setchell), on tidal current velocities and sediment texture was studied at Harwood, Otago Harbour, New Zealand. Tidal current velocities were substantially reduced inside the Z. novazelandica patch compared to velocities above the patch (3.7 times greater) and outside it (2.5 times greater), causing a low-flow environment among the 12-cm-tall seagrass. Current velocities combined over one tidal cycle occupied a much wider range outside (1.2-A.b cms-1) and above (1.9–7.1 cm s-1) the seagrass patch than inside (0.1–1.8 cm s-1) indicating slower and less variable water flow. Suspended mud (<0.063 mm) settled to the bottom in this low-energy environment and was protected from resuspension by seagrass cover, indicated by significantly elevated amounts of mud inside the seagrass patch (1.1%) compared to outside (0.4%). These results indicate that Z. novazelandica may reduce water flow and accumulate finer sediment sizes to a lesser extent than larger subtidal seagrass species. © 2000, Copyright Taylor & Francis Group, LLC.