University of Tasmania
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Safe in my garden: reduction of mainstream flow and turbulence by macroalgal assemblages and implications for refugia of calcifying organisms from ocean acidification

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posted on 2023-05-21, 04:25 authored by Kregting, L, Damon BrittonDamon Britton, Craig MundyCraig Mundy, Catriona HurdCatriona Hurd

Macroalgae, with their various morphologies, are ubiquitous throughout the world’s oceans and provide ecosystem services to a multitude of organisms. Water motion is a fundamental physical parameter controlling the mass transfer of dissolved carbon and nutrients to and from the macroalgal surface, but measurements of flow speed and turbulence within and above macroalgal canopies are lacking. This information is becoming increasingly important as macroalgal canopies may act as refugia for calcifying organisms from ocean acidification (OA); and the extent to which they act as refugia is driven by water motion. Here we report on a field campaign to assess the flow speed and turbulence within and above natural macroalgal canopies at two depths (3 and 6 m) and two sites (Ninepin Point and Tinderbox) in Tasmania, Australia in relation to the canopy height and % cover of functional forms. Filamentous groups made up the greatest proportion (75%) at both sites and depth while foliose groups were more prevalent at 3 than at 6 m. Irrespective of background flows, depth or site, flow speeds within the canopies were <0.03 m s–1 – a ∼90% reduction in flow speeds compared to above the canopy. Turbulent kinetic energy (TKE) within the canopies was up to two orders of magnitude lower (<0.008 m2 s–2) than above the canopies, with higher levels of TKE within the canopy at 3 compared to 6 m. The significant damping effect of flow and turbulence by macroalgae highlights the potential of these ecosystems to provide a refugia for vulnerable calcifying species to OA.


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Frontiers in Marine Science



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Institute for Marine and Antarctic Studies


Frontiers Research Foundation

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Copyright © 2021 Kregting, Britton, Mundy and Hurd. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) License ( The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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