Mr Francois Thoral1,2, Dr Matthew Pinkerton2, Dr Leigh Tait2, Prof David Schiel1
1University Of Canterbury, Christchurch, New Zealand, 2National Institute of Water and Atmospheric Research (NIWA), Wellington, New Zealand
Compromised light quantity on the seabed affects the resilience of marine forests, the composition of macroalgal assemblages, and the maintenance of ecosystem services associated with these habitats. However, the response of macroalgal assemblages to changes in the quality (spectral composition) of light as compared to purely the quantity is poorly understood. Here, we bridge radiative transfer modelling and algal physiology to simulate the underwater light environment and explore macroalgal responses to spectral attenuation by coastal water constituents. We considered three groups of macroalgal taxa (class phaeophyceae and phyla chlorophyta and rhodophyta). For each, we developed an envelope of spectral absorption profiles and action spectra (1 million radiative simulations). We found that brown macroalgae were more efficient at harvesting spectral benthic light at relatively lower attenuation (<0.2 m-1) and at deeper conditions (>10 m depth), whereas green macroalgae were dominating shallower depths (<10 m) and for low to high attenuation values. Finally, red macroalgae made most use of the available spectral light at relatively higher attenuation values (>0.2 m-1) and deeper depths (>10 m). We show that phytoplankton and sediments not only reduced the amount of light on the seabed but also removed crucial colours, affecting macroalgal taxa differently, especially at depths beyond 10 m. Our work sheds light on how changes in light quality can lead to shifts in macroalgal communities in low light environments. This study enables new applications of remote sensing by linking satellite-derived ocean colour products to ecological transitions between macroalgal assemblages.
Presentation Slides – Francois Thoral
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