An in situ study of production from diel oxygen modelling, oxygen exchange, and electron transport rate in the kelp Ecklonia radiata

Macroalgal forests provide the foundation for most shallow reef ecosystems in temperate environments; hence tools for accurately measuring primary productivity are integral for ecosystem management. This study compares estimates of production/potential production in an Ecklonia radiata kelp forest in Tasmania, Australia, using diel oxygen gross primary production (GPP) models, benthic exchange chambers, and electron transport rate in photosystem II measured using PAM fluorometry. Two approaches to modelling GPP show good fit with environmental dissolved oxygen (DO), with gross oxygen production of the kelp bed ranging between ~0−20 for one model and ~0−8 µmol O₂ m⁻² s⁻¹ for the other, with total daily GPP (±SE) of 464 ± 28 and 347 ± 7 mmol O₂ m⁻², respectively. The oxygen production rate of E. radiata in benthic chambers ranged between 0 and 9.6 µmol O₂ m⁻² s⁻¹, with total daily production as 204 ± 13 mmol O₂ m⁻², half that estimated from modelling DO. The peak value for maximum relative electron transport rate was 49 µmol e^– m⁻² s⁻¹ at PAR of 208 µmol m^–2 s⁻¹. Oxygen evolution from benthic chambers and electron transport rates from PAM fluorometry were well correlated; however, the latter may overestimate oxygen production. Water column DO can measure GPP of the benthic communities; however, additional measurements/more sophisticated models may be necessary. Benthic exchange chambers and PAM fluorometry can potentially estimate the contribution of E. radiata to total daily production provided that the measurements can be calibrated with other methods to obtain actual productivity. Additionally, upscaling requires reliable biomass estimates.