Dr Steph Mangan1, Dr Leigh Tait2, Mr Shawn Gerrity1, Prof David Schiel1
1University of Canterbury, Christchurch, New Zealand, 2National Institute of Water and Atmospheric Research, Christchurch, New Zealand
Macroalgal-dominated habitats are becoming recognised for their significant contribution to global carbon cycling. However, relatively little is known about the variation of productivity over large spatial-temporal scales and the relative importance of environmental and biotic factors in influencing the quantity of carbon fixed. Here we leverage a tectonic event to understand how fluctuations in the standing biomass of habitat-forming seaweeds and changes in light availability influence primary productivity and thus carbon fixation along 130 km of coastline over 5 years. Furthermore, we quantify the broader implications of changes to species composition on carbon fixation. This study revealed significant implications of a compromised light environment on both standing biomass of macroalgae and carbon fixation rates. Immediately post-earthquake, there was a substantial loss of biomass (average -83 %) of a large alga, Durvillaea spp., and very limited recovery over the next 5 years. Earthquake-induced reductions in biomass coupled with changes in light attenuation resulted in average net primary production (NPP) from Durvillaea spp. decreasing from 1130 g C m-2 y-1 before the earthquake to 192 g C m-2 y-1 after 5 years. Partial compensation of NPP was facilitated by increases in the biomass of another fucoid, Carpophyllum maschalocarpum, but its productivity was considerably less on average, resulting in a reduction carbon fixation rates. Overall, reductions in biomass resulted in a 2-10 fold drop in carbon fixation by canopy-forming seaweeds over at least 5 years and a degradation of the light environment, further compromising primary productivity and blue carbon export potential.
Presentation Slides – Steph Mangan
