Seaweed forests exhibit exceptionally high per-area production rates, however measuring this productivity in situ can be challenging. We have developed novel methods to quantify net community metabolism in macroalgal forests, demonstrating that these habitats draw the largest carbon flux by any vegetated habitat in the coastal ocean and are indeed net autotrophic systems. The assumption that these habitats are therefore carbon sinks, however, requires further dissection. Macroalgae release up to 35% of their net primary productivity as dissolved organic carbon and these habitats can also release methane emissions which may counterbalance atmospheric CO₂ uptake. Importantly, macroalgal forests contribute substantial detritus which can reach marine sediments where it may potentially be sequestered. For macroalgae to contribute meaningfully to carbon sequestration, however, it’s detritus must be under environmental conditions such that it decomposes slowly and/or incompletely, increasing the probability of permanent burial in sediments. There have been numerous estimates of algal degradation rates in the shallows, and some limited estimates of carbon loading rates to deep sea sediments. But we lack a mechanistic understanding of how the degradation of algal detritus varies with depth and how it might degrade during its journey. We are exploring whether macroalgae in the Baltic Sea, with cold temperatures and low oxygen levels, relative to other regions, can serve as a useful model system for understanding macroalgal carbon turnover and potential sequestration. 

Primary Presenter: Lydia White, Tvärminne Zoological Station, University of Heksinki (lydia.white@helsinki.fi)

Authors:

Lydia White, Tvärminne Zoological Station, University of Helsinki  (lydia.white@helsinki.fi)

Alf Norkko, Tvärminne Zoological Station, University of Helsinki  (alf.norkko@helsinki.fi)